Strange cooling problem - what do yo think it is?

Chevy 355, Holley systemax kit, Holley 750 carb. Advance curve kit, static timing about 16 degrees (per Holley instructions for cam). Dual electric fans, 180 T-stat, 3 core brass radiator. 16lb rad cap, 50 oz overflow tank.

After the engine gets up to 180, the thermostat opens and the temp stays there for about 10 minutes. Then the temp jumps (in about 15 seconds) to about 240. Within a minute it comes down to about 200 and stays there, sometimes going up to 210-215 depending on how hard I drive it. It does this if I am on highway speed, city, whatever. Always about 10 minutes into hot.

I am trying to figure what the cause is of the sudden heat? If the radiator was not efficient enough, why would it be ok for 10 minutes. Is there something in the engine heating up (intake maybe) causing a lack of proper cooling?

I will be installing a 2 core cross flow aluminum radiator, and a Taurus electric fan (4000 cfm for $50) soon, but I would still be curious on what opinions are on the cause.

Pnut mine acts like that too. I think sometimes my water pump pumps so fast that when I slow down it asorbs the heat rapidly. Hows the fishing on the Rabbit this year?

could be the location of your sending unit too

Also check the rad cap and whether or not the lower rad hose is collapsing once it gets heated up.

I had the same problem added a spring in the lower radiator hose due to it collapsing when hot. Cured problem.

Thanks for all the ideas.

I am pretty confident that the thermostat is operating properly because it is the 2nd one (same result), and the temp always comes up to 180, then sits there for about 10 minutes (the tstat is 180).

The lower hose is corrugated stainless hose, and for sure is not collapsing.

The rad cap is opening up at 16PSI (2nd one just happen to have 2 good ones around).

I think it may be just the engine heat taking 10 minutes to heat soak the front of the intake (where the sensor is) right next to the tstat.

Good idea about the heat gun, we have one at work. Again, thanks guys for the opinions and advice.

I had a wierd thing going on with my motor. I ended up drilling a small hole in the thermostat, so a small amount of water would always be flowing. It stabalized the indication issues I had due to the postion of the sending unit.

Keith...

why are you only going 2 core radiator with your new one.... not enough room for a 3core?

I did also drill a 1/8" hole in the t-stat for water burping...


Why only 2 core?
After doing my own research mostly online and talking to race shops on the phone, I have found that a 2 core (1" cores) CROSSFLOW aluminum radiator will cool much better than even a 4 core brass radiator, and that those 2 core aluminum ones will cool just about anything (the newest models without epoxy, furnace brazed cores). A friend of mine running an 1100hp big block uses the same size crossflow radiator and it is enough for his, so I figure good enough for mine. A different good friend has a Jeep with a big block in it, and he runs 160 all day with the same radiator I plan to buy. Good comparison there.

Thanks for the advice guys. Did the impeller disc install last night, with the radiator on the way. I am interested to see the cooling result.

the 1100hp example isn't a good one because that sounds like a drag car, i know a lot of drag cars that dont even run radiators and dont have overheating problems because they're only going a 1/4 of a mile

yes and a 1100 hp engine will not make that at a idle so by the time you make that 1100hp you have alot of air flow:eek: this also would have to do with how much gear you have in it for the hi speed air flow and if the cops can catch you:whacked:

I've seen that same temp variation a few times, always with aluminum intakes. I just learned to live with it.