Overheating Mystery

Can't figure out why my 350 engine is overheating. Bought this 55 Bel Air from my cousin. Had been re-built 2000 miles ago using a Summit Racing Performance Kit...Stage 1 Cam, High compression heads, edlebrock intake and carbuerator, headers....runs awesome if I could keep it from climbing up to 240 degrees!

Found out that the radiator was trash....super rusty inside. Car had been sitting and not being driven for a long period....maybe a year or more.

I added a Champion radiator...aluminum. Added a new 14" 2450 CFM fan, new shroud, and new water pump. I have tried running the car with and without thermastats. No luck!

This is what happens. Car runs very cool with no thermastat for about 10 minutes...mabye even 15 minutes.....stop and go traffic, waiting at street lights etc...not freeway driving.

Slowly, the engine creeps up to temp....I mean a long time I imagine is 15 minutes....4-5 miles of slow stop and go driving....so seems to be holding at 190....200.....but then boom! The car goes to 205, 210, and keeps climbing slowly.

I have recenly soaked the engine and new radiator etc in CLR, Radiator flush....even Vinegar! 2 days of vinegar.....1 day of CLR.....3 days of radiator flush. Went today for a pressured radiator flush...vacuum and pressure...so backflushed, and forward flushed, and replaced all fluids. Took off the electric fan and shroud, and added a bolt on blade fan....seems to be pulling more air, but no shroud yet and it's super close to the radiator, so that's a problem.

But test drive after the new fan mod, and pressure flush after 3 days of soaking the engine and still doing the same darn thing....just a slow increase of delayed temp rise, and then overboard. Still no thermastat in the car.

Could it really be just a fan shroud needed at this point, even though it's still doing the same thing with heating up over such a long, slow time?

Im really looking for help. I have no water in the engine oil. I puff no smoke out the tail pipes....engine runs really strong...love it!

What else can I look out before throwing in the towel and stripping the entire engine down?

Thanks for your help......Im attaching some pics of the old radiator and water pump that I have removed to give you idea of what I was looking at when I started replacing stuff.

Where on the engine do you have the sensor mounted? Have you checked the timing throughout the rpm range? Are the hoses new as well, or reused? Are you sure your gauge is working properly?

My first thought, reading your explanation was, "I wonder if there's a spring in the lower radiator hose to keep it from sucking shut as it gets hot and the rubber gets softer?"
BTW, with no thermostat the coolant can flow so fast that it doesn't have time to lose heat in the radiator. Some old school guys used to run a restrictor in place of the 'stat, a big washer with the hole sized to drop the flow where it worked. A good 'stat is better, and the right way.

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Originally Posted by Bob Parmenter

Where on the engine do you have the sensor mounted? Have you checked the timing throughout the rpm range? Are the hoses new as well, or reused? Are you sure your gauge is working properly?

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I have checked the temp comparison to the gauge using my temp gun and it's within 5 degrees. Sensor is mounted on the intake.

I do need to add a Spring to the lower hose but have rigged it by adding a hose clamp around the bend of the hose and can see there is no pinching when hot. Maybe I should just replace the lower hose with one more rigid. The pressure does get pretty intense as you would predict.

I'm going to add a spacer to the fan to get it within 1 inch of the radiator. Replace the thermostat. Try again and pray.

Does it have AC, with condenser in front of radiator? This could be preheating your air through the radiator.

There should be plenty of room under the hood for a stock style fan and shroud. If not you might have to change to a short water pump if possible since that would require pulley changes as well. A stock system with at least a 180º thermostat will keep it cool. My 76 Vette runs a stock system with a 195º thermostat and I don't drive often in heavy traffic and it stays right at 200º.

Did the car get hot like this before you bought it as well, or just after it sat for a long time?

looks like the rad is full of stopleak .

LOL, I was thinking the same thing! And once you get the cooling system flushed enough the real symptom will show up.

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Originally Posted by MP&C

Does it have AC, with condenser in front of radiator? This could be preheating your air through the radiator.

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No A/C unfortunately....go fish!

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Originally Posted by NTFDAY

There should be plenty of room under the hood for a stock style fan and shroud. If not you might have to change to a short water pump if possible since that would require pulley changes as well. A stock system with at least a 180º thermostat will keep it cool. My 76 Vette runs a stock system with a 195º thermostat and I don't drive often in heavy traffic and it stays right at 200º.

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I like 76 Vett's.....NICE! Im gonna replace the shroud too.....just bought a spacer for the fan to move it right up to the radiator and into the 4" shroud.....Replace the thermastat and take it on a freeway ride. If it stays cool enough on the freeway.....but overheats in stop-n-go traffic, then I will add two pusher fans on the front of the radiator. Hope that works!

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Originally Posted by 40FordDeluxe

Did the car get hot like this before you bought it as well, or just after it sat for a long time?

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I never heard anything about it over heating from my cousin...but then again, he let the car sit on a new engine for a year or more...maybe very light short drives for a couple years so I don't think he noticed. It has been running hot and overheating since I got it.

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Originally Posted by shine

looks like the rad is full of stopleak .

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That was the old radiator that I removed. Same problem with the new aluminum radiator....

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Originally Posted by 36 sedan

LOL, I was thinking the same thing! And once you get the cooling system flushed enough the real symptom will show up.

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Did you think that the radiator had stop leak in it? I hadn't thought of that....and now that you mention it, that radiator was older, so maybe a mechanic or someone added stop leak to it and forgot to flush it......Now Im thinking what more shit would that have clogged up having sat like that for so long. One thing I don't know is how small any of the water passages are in this engine, and I can imagine that if small like a pencil, those could easily clog up with rust and chunks from the deteriating radiator I removed. Thoughts?

Add an oil cooler.

My better judgement tells me to refrain, and I certainly don’t want to hurt anyones feeling or come off as a know it all or bully again. I have been down this rabbit hole before.
So in the spirit of answering your question as it pertains to my own experience (which may or may not apply to yours). My symptoms were like yours; tried several new thermostats, new fans, new water pumps (even high flow pumps), flushed motor and had radiator boiled out at a radiator shop, even installed a new radiator, tried different types and ratios of anti-freeze, even straight water yet no difference. I had resigned myself to drive it in cool weather only.
One cold winter morning I decided to take a little cruise in the cool weather, started it up and ran for about 30 seconds then suddenly started spewing smoke everywhere, it was a real James Bond moment. The exhaust smoke had this familiar smell to it, but I could not place it, for some reason I decided to look in the radiator and as I released the cap pressure came out, way too much pressure for 30 seconds. The ahhh moment when I remember what burning antifreeze smells like. Previous owner had doctored a leaking head gasket with stop leak, all the flushing I did finally made it let go.

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Originally Posted by 36 sedan

My better judgement tells me to refrain, and I certainly don’t want to hurt anyones feeling or come off as a know it all or bully again. I have been down this rabbit hole before.
So in the spirit of answering your question as it pertains to my own experience (which may or may not apply to yours). My symptoms were like yours; tried several new thermostats, new fans, new water pumps (even high flow pumps), flushed motor and had radiator boiled out at a radiator shop, even installed a new radiator, tried different types and ratios of anti-freeze, even straight water yet no difference. I had resigned myself to drive it in cool weather only.
One cold winter morning I decided to take a little cruise in the cool weather, started it up and ran for about 30 seconds then suddenly started spewing smoke everywhere, it was a real James Bond moment. The exhaust smoke had this familiar smell to it, but I could not place it, for some reason I decided to look in the radiator and as I released the cap pressure came out, way too much pressure for 30 seconds. The ahhh moment when I remember what burning antifreeze smells like. Previous owner had doctored a leaking head gasket with stop leak, all the flushing I did finally made it let go.

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First of all, thanks for your comments. I am confused why you thought it better to refrain when your experience had such similarities to my situation. Your experience is exactly what I am looking for.

Thanks to you and others, we have noted that the radiator very well could have had stop-leak left inside it. You think maybe that the reason for the stop leak was for a head gasket? I only pause because I know the freshness of the engine and don't believe that could or would have happened without my cousin telling me, unless his mechanic did this as a band-aid and never told him. I guess anything is possible. My cousin is not mechanical and relied 100% on his mechanics. I figure the radiator might have had a leak, and the stop-leak was forgotten. Question is now, why does it overheat? Is it possible I have a head gasket problem that is causing the overheating? How would that work without showing water in the oil, or any smoke coming out the pipes?

I did run the car tonight as suggested earlier to check on the exhaust system, and see if the pressure was any different coming out one side or the other. I did feel a slight difference actually. I started the car after setting the choke, and put my hand over each tail pipe, and although I did notice a difference in pressure, it was not significant. I was hoping for more of a noticable difference. I would say 10-15 percent less pressure on one side. I think the two sides are set up the same way....both have headers and both have turbo flow mufflers. Maybe one side has a bad muffler? Other than the possible rat or frog (lol) being stuck in one pipe which I can't imagine would slow much flow down, what could this be or is there a pressure test to see if the exhaust is causing this problem of overheating? Or are we settling on stop-leak as the culprit and the engine needs to be opened up? Heads off and dealt with?

Please don’t misinterpret, I’m not trying to tell you what you should do, rather what my experience was.

IMHO, I will suggest you should do some testing on your motor:

1). Does your motor over heat a idle (stopped) as well as on the highway (cruising)? If only at idle, more than likely you do not have enough low speed air flow (fan). If both, you need to test further.
2). Check your total timing, make sure your mechanical and vacuum advance are working properly. I would suggest total timing be between 32°-36° and all in by 2500rpm (vacuum advance disconnected at this time). If you have vacuum advance check to see how much it adds at idle and cruise rpm (I would suggest 10°-12° vacuum advance max). Timing will cause heating problems.
3). Use your timing light on each wire at the spark plug, it will tell you if spark is getting to the plug (light will flash), a miss can cause over heating.
4). Pull the plugs keeping them in order as to which cylinder they came from and examine them. The plugs will tell you a lot about your motor’s condition and keeping them in order will show which cylinder is suspicious.
5). While the plugs are out do a compression test, verify all cylinders are within 10% of each other and compression is sufficient to support combustion. If you have two adjacent cylinders with lower compression (especially 3&5, 4&6 on SBC), usually this indicates a head gasket, you can squirt a little oil in these cylinders and re-test their compression to see if the rings are a problem (the oil will raise the compression by momentarily sealing the rings).
6). While the plugs are out, check valve adjustment. Poorly adjusted valves can cause low compression and heating problems.
7). Check the air/fuel ratio, a lean motor runs hot. Some smog check stations will test the air/fuel ratio reasonably for you.
8). Check the flow rate through your radiator, with the cap off, warm your motor to thermostat opening while watching the flow, when the thermostat opens you should see a significant change in water flow. Put the cap on and feel the upper and lower hoses (careful hot), the upper hose should feel firmer than the lower. If both feel firm, you probably have too much restriction, check for a clogged hose or passage.
9). If you suspect an exhaust blockage, un-cap your headers and run to see if it corrects problem.

Again just my opinion and suggestions, not trying to tell you what or what not to do, or insult anyone, simply trying to help you find the problem.

This article has helped me before, it covers just about everything mentioned and then some. My engine overheats, what should I be looking for?

36Sedan has good tips....can I add some quick checks that cost nothing and can be done in seconds?
1. These days, there are TWO different sbc water pumps....standard rotation and reverse rotation for
the serpentine belts. There are TWO different fans, the old standard and the reverse rotation for
serpentine belts.
2. A easy first check is to put a piece of paper at the front of the radiator. If the paper blows off,
you have a backward fan for your belt setup. I made this mistake once, I had changed to a serpentine
setup but forgot to change the fan blade....I was leaning on the core support and the wind was blowing
towards me....oops. Truck cooled great at idle and at high speed....but a moderate speed, the
fan wind cancelled the speed wind and it got hot.
3. Checking the water pump flow is tougher. A wrong way pump will still pump a little bit but it
wont pump full flow. You cannot tell which direction the pump impeller is designed for without taking
the back off the water pump....there is no exterior casting identifier. A wrong way impeller pumps
significantly less fluid but does pump so it will confuse things. It is common to have the wrong pump
in a new box at the auto supply...ugh. Anyone know of a reliable test for the impeller?

Had some more time to work on Bella.....checked the timing, and it was about 8. Moved it to 10. Changed the radiator cap that had a small leak, added a new radiator overflow tube...the old one had melted a bit and was pinched. Added a 3" spacer to the water pump pulley to bring the fan 3" closer to the radiator, and that greatly increased the flow, and got some paper sticking to the frontside of the radiator. Took the car for a drive on the freeway this time, and it was a cool 65 degrees outside....nice late afternoon for a cruise. No thermastat and car ran super cool on the freeway....8 miles North, up a nice 2 mile grade, and never got over 160. Got off the freeway, turned around, came home 8 miles and exited at 160 as well. Hmmm.....well that is sweet. Maybe the head gasket isn't cracked after all? Maybe the temp just never got hot enough to open the crack and start letting exhaust into the cooling system? Came to the exit on the freeway and caught the red light....well that was good I though and could test some idle time after having driven 16 miles and all was good. Yup....after about a minute and a half, she started to climb. But only to 170. Then I putted home 1/4 a mile, and by the time I backed her in, she was 175. So definitely going up at slow speed. I didn't wait to see if she would continue to climb as before, and just quit while I was ahead. From what I have read, I can almost be sure that I just need more air coming through the radiator. So if this is the case, I will build a fan shroud this weekend, and can also add two smaller pusher fans to the front of the radiator for extra support. I actually don't mind leaving the thermastat out....Sunny California/Los Angeles, Im not worried too much about the cold weather coming:) I know there are other things to check as you mentioned, and I still have those in my pocket if I need to do that other stuff....and maybe I will in time. I did check the timing order of the distributor and plugs.....1-3-5-7 2-4-6-8 and read up a bit on that while playing with it. Thanks for all the tips...I will reference this post often and have saved it to my notes.

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Originally Posted by 36 sedan

Please don’t misinterpret, I’m not trying to tell you what you should do, rather what my experience was.

IMHO, I will suggest you should do some testing on your motor:

1). Does your motor over heat a idle (stopped) as well as on the highway (cruising)? If only at idle, more than likely you do not have enough low speed air flow (fan). If both, you need to test further.
2). Check your total timing, make sure your mechanical and vacuum advance are working properly. I would suggest total timing be between 32°-36° and all in by 2500rpm (vacuum advance disconnected at this time). If you have vacuum advance check to see how much it adds at idle and cruise rpm (I would suggest 10°-12° vacuum advance max). Timing will cause heating problems.
3). Use your timing light on each wire at the spark plug, it will tell you if spark is getting to the plug (light will flash), a miss can cause over heating.
4). Pull the plugs keeping them in order as to which cylinder they came from and examine them. The plugs will tell you a lot about your motor’s condition and keeping them in order will show which cylinder is suspicious.
5). While the plugs are out do a compression test, verify all cylinders are within 10% of each other and compression is sufficient to support combustion. If you have two adjacent cylinders with lower compression (especially 3&5, 4&6 on SBC), usually this indicates a head gasket, you can squirt a little oil in these cylinders and re-test their compression to see if the rings are a problem (the oil will raise the compression by momentarily sealing the rings).
6). While the plugs are out, check valve adjustment. Poorly adjusted valves can cause low compression and heating problems.
7). Check the air/fuel ratio, a lean motor runs hot. Some smog check stations will test the air/fuel ratio reasonably for you.
8). Check the flow rate through your radiator, with the cap off, warm your motor to thermostat opening while watching the flow, when the thermostat opens you should see a significant change in water flow. Put the cap on and feel the upper and lower hoses (careful hot), the upper hose should feel firmer than the lower. If both feel firm, you probably have too much restriction, check for a clogged hose or passage.
9). If you suspect an exhaust blockage, un-cap your headers and run to see if it corrects problem.

Again just my opinion and suggestions, not trying to tell you what or what not to do, or insult anyone, simply trying to help you find the problem.

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Just an observation, but, the pusher fans will actually block airflow and in some situations cause the temps to rise.

the thermostat is not just for cold weather. it is for keeping coolant in the rad so it can exchange heat . without it you will just keep getting hotter.

At the risk of helping and not offending, if I’m bothering anyone I’ll leave again.

Please check your total timing, 10° initial timing may still be wrong.
I’ll tell why, initial timing is rpm sensitive, meaning the mechanical advance can and will effect initial timing depending on idle speed. While most distributors do not engage mechanical advance below 1000rpm, I have seen some that start at 800rpm and slightly lower. If idle speed is higher than 800rpm, your mechanical advance may have started its curve, if you set initial timing to 10° you may actually only have 28° - 30° total timing and robbing your motor of a lot of power while producing too much heat in the motor (especially at idle).

Total timing is easy to set; you will need an adjustable timing light or a standard timing light and a roll of timing tape that matches your harmonic balancer (SBC is usually a 6.75” O.D. or 8” O.D.).

STANDARD TIMING LIGHT METHOD, install the appropriate timing tape, disconnect your vacuum advance and plug the vacuum line going to the carb. Have a buddy sit in the car and bring the motor rpm up to 3500rpm and hold it, using your timing light adjust the timing to read 34° - 36° on the timing tape. Now have your buddy bring the rpm up to 4200rpm and check, adjust if needed. This is your TOTAL TIMING. Let your motor idle and adjust idle speed as need.

ADJUSTABLE TIMING LIGHT METHOD, disconnect your vacuum advance and plug the vacuum line going to the carb. Adjust your timing light to read 34° - 36°, have a buddy sit in the car and bring the motor rpm up to 3500rpm and hold it, adjust your timing to zero at the timing tab on the motor (the timing light has adjusted to the correct timing). Now have your buddy bring the rpm up to 4200rpm and check, adjust if needed. This is your TOTAL TIMING. Let your motor idle and adjust idle speed as need.

Your initial timing will now be whatever it is, usually 12° - 14° (below 800rpm idle). Initial timing is not critical, TOTAL timing is. Now drive your car hard, listen for any pinging, rattling, knocking type noise while accelerating. If you hear any noises described above, lower total timing 2° and test again, adjust as needed to eliminate detonation.

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Originally Posted by 36 sedan

At the risk of helping and not offending, if I’m bothering anyone I’ll leave again.

Please check your total timing, 10° initial timing may still be wrong.
I’ll tell why, initial timing is rpm sensitive, meaning the mechanical advance can and will effect initial timing depending on idle speed. While most distributors do not engage mechanical advance below 1000rpm, I have seen some that start at 800rpm and slightly lower. If idle speed is higher than 800rpm, your mechanical advance may have started its curve, if you set initial timing to 10° you may actually only have 28° - 30° total timing and robbing your motor of a lot of power while producing too much heat in the motor (especially at idle).

Total timing is easy to set; you will need an adjustable timing light or a standard timing light and a roll of timing tape that matches your harmonic balancer (SBC is usually a 6.75” O.D. or 8” O.D.).

STANDARD TIMING LIGHT METHOD, install the appropriate timing tape, disconnect your vacuum advance and plug the vacuum line going to the carb. Have a buddy sit in the car and bring the motor rpm up to 3500rpm and hold it, using your timing light adjust the timing to read 34° - 36° on the timing tape. Now have your buddy bring the rpm up to 4200rpm and check, adjust if needed. This is your TOTAL TIMING. Let your motor idle and adjust idle speed as need.

ADJUSTABLE TIMING LIGHT METHOD, disconnect your vacuum advance and plug the vacuum line going to the carb. Adjust your timing light to read 34° - 36°, have a buddy sit in the car and bring the motor rpm up to 3500rpm and hold it, adjust your timing to zero at the timing tab on the motor (the timing light has adjusted to the correct timing). Now have your buddy bring the rpm up to 4200rpm and check, adjust if needed. This is your TOTAL TIMING. Let your motor idle and adjust idle speed as need.

Your initial timing will now be whatever it is, usually 12° - 14° (below 800rpm idle). Initial timing is not critical, TOTAL timing is. Now drive your car hard, listen for any pinging, rattling, knocking type noise while accelerating. If you hear any noises described above, lower total timing 2° and test again, adjust as needed to eliminate detonation.

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Good info and besides this isn't hotrodders and we don't have an hcompton, thank goodness.

exactumundo ! i try to idle down to 500 if possible.
but you are absolutely right on retarded timing . also a good way to burn up a set of headers.

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Originally Posted by 34_40

Just an observation, but, the pusher fans will actually block airflow and in some situations cause the temps to rise.

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I was worried about that too! I even suspected that when I installed my electrick fan and shroud earlier.....Im gonna make that big shroud today and see how that helps...Im sure it will increase focus on the air coming through the radiator by 50% at least!

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Originally Posted by shine

the thermostat is not just for cold weather. it is for keeping coolant in the rad so it can exchange heat . without it you will just keep getting hotter.

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I thought so too, but have heard different philosophies on that....maybe engine specific? I even think earlier in this thread it was commented that no thermastat is need on 350 Small Blocks. I get the principle you are mentioning....

Chevy v8 firing order is 1 -8-4-3-6-5-7-2

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Originally Posted by 36 sedan

At the risk of helping and not offending, if I’m bothering anyone I’ll leave again. .

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Leave? You better not leave!! :mad:

You're one of the good guys, we need more folks like you 'round the place.:cool:

As always, it's good to see you here again, and don't go to far off.. I always know where to go when I have an electrical type question.:3dSMILE:

Turns out the head gasket or gaskets are bad. I did a combustion lead detection test using the funnel with blue liquid, and the first puff of air coming through the liquid immediately changed the color of the fluid to yellow. In a flash! So.....that's pretty much the answer the to mystery. Now to pull the heads off and see why the gasket/s failed. New engine too. Bad build? Bad heads? Cracked heads or block? All possibilities out on the table. Dang!

I should also have mentioned, that the engine runs great at moving speeds.....freeway driving is a breeze and never gets hot. Only at idle, or in traffic will it heat up. I think the new radiator and fan with shroud can keep up with the gasket leak. Crazy problem, and really no visible symptoms. No water in the oil, no smoke out the back.....no nothin! Just combustion exhaust leaking into the water jackets, heating up that coolant! Learn something new every day!

Who built the engine?

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Originally Posted by NTFDAY

Who built the engine?

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Not sure, but think it was an Australian guy "Mobile Mechanic".....someone my cousin knows and did the work before I bought the car. I have been in touch with the guy and he's been great answering the phone and helping me along. Seems like a really nice guy....and gave me a machine shop to work on the heads after I pull them off...$300 for the pair to be re-surfaced, and pressure tested....and some mention about the valves. Sounds way better than I thought.