Thread: Delayed overheating problem

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34_40:
Is this the bobbet style?



If so then that's what I have and I'll go grab a sleeve thermostat. Funnily enough, when I first started the engine it was overheating really badly. So I replaced the thermostat, but it still was overheating. So I grabbed the thermostat and stuck it in a pot of boiling water to make sure it was actually opening. Was really cool to watch, and it did indeed work. Installed the 4 inch spacer on the fan and it cooled much better just idling in my driveway so I left it at that.I will definitely try to get the fan in the shroud more, I think I still have that 2" spacer around here somewhere, I'll go get longer bolts today.


rspears:
I appreciate the guidelines for the fan dimensions, I'll make sure to get it within those tolerances. I also appreciate the advice on the electric fan, you just saved me a lot of time and money. That was also an interesting read, I guess another benefit of the mechanical fan is reliability (if it's set up correctly haha).


Mike P:
You very well could be on to something, the gauge is stock so it could be faulty. My reason for thinking it is overheating is that it goes to the redline, then slowly goes back down to the middle line (210) and stays there for the rest of the trip. That's also a good point about the flex fan, it was a pretty cheap fan and could very well be doing that. The blades flex out when at higher rpms because there is more air moving over the radiator right? What never made sense to me was that if this concept is aimed at cooling the radiator at more efficient rates, doesn't it "reset" when you change gears and the rpms drop? I have the old fan sitting in my parents garage in Oklahoma, I'll look into the cost of getting it up here.


firebird77clone:
I actually had to replace the radiator during the rebuild because the old one had a horrible leak in it. Before I rebuilt the engine I had the block cleaned in a vat at a shop so hopefully there was nothing in the system, but anything is possible, especially with my luck. Can I do a flush/service myself?


NTFDAY:
Timing is a bit of an issue right now, actually a pretty big issue. The engine I have I got from a scrapyard (2 bolt main 350 originally from a 1972 Chevelle, at least that's what they told me) and didn't come with the bracket for doing timing adjustment (you use a timing light to compare the harmonic balancer with the bracket right?). Although I did buy a timing light. So to adjust it I just turned the distributor one way until the engine stumbled, then turned it the other way until it stumbled and set it at the middle ground. I did the same thing with the air/fuel mixture screw on the carb. However, these are two separate variables that effect each other, so I feel like using this method on both is really difficult to get everything right. It almost seems like a system of linear equations.

Check the counter weights under the module in the dist and make sure they move freely. If you have a vacuum gauge you can get the timing fairly close, adjust for the highest reading and back it off just a tad and you'll be in the ball park and you can do the same with the air/fuel mixture screws on the carb except you adjust for the highest steady reading. Old radiator hoses do have a tendency to collapse under pressure and heat and will restrict water flow.

Originally Posted by NTFDAY

Old radiator hoses do have a tendency to collapse under pressure and heat and will restrict water flow.

Along the lines of checking the simple things first, you do have a spring inside the lower radiator hose, right? If not you could be sucking that hose closed as rpm's increase, severely reducing your flow. And when you say you had to get another radiator, that was a new/rebuilt unit and not one from the salvage yard, right?

Originally Posted by NTFDAY

Check the counter weights under the module in the dist and make sure they move freely. If you have a vacuum gauge you can get the timing fairly close, adjust for the highest reading and back it off just a tad and you'll be in the ball park and you can do the same with the air/fuel mixture screws on the carb except you adjust for the highest steady reading. Old radiator hoses do have a tendency to collapse under pressure and heat and will restrict water flow.

I actually do have a vac gauge, will try that right now. I appreciate it! And after testing the hoses by pinching them I think you're definitely on to something.

Originally Posted by rspears

Along the lines of checking the simple things first, you do have a spring inside the lower radiator hose, right? If not you could be sucking that hose closed as rpm's increase, severely reducing your flow. And when you say you had to get another radiator, that was a new/rebuilt unit and not one from the salvage yard, right?

Interesting, I just went in the garage to try squeezing the lower hose and it compressed way easier than I was expecting. Also way easier than when I first installed the hoses, which could explain why I never used to have this initial overheating problem after I initially fixed the problem with a bigger fan. The upper hose was a lot weaker as well. Although I don't have to worry about the upper hose because it has positive pressure and the lower hose has negative pressure right? Also would O'Reillys have the springs I need for the lower hose? And I replaced the radiator with a brand new one.


As a side note, after a 10-15 minute drive the starter really struggles to turn it over. I replaced the starter just last week with one of those cheap ebay "3 hp" electric starters from DB electrical (I was hesitant at first but read good reviews about it), because the old starter I was using had stopped working. When cold, or mildly warm, it starts beautifully, much faster than the old starter. But just yesterday I was driving home from the grocery store and pulled into the driveway. Got out to open the garage door, then started it back up to drive in and it really struggled to turn it over.

Bit of an update:

Just tried revving it with the hood open and watching the lower radiator hose, it doesn't really seem to collapse, but maybe that's because it wasn't fully warmed up yet. Will get it warmed up while adjusting the carb/timing and try again. Here's some pics of the fan inside the shroud, now that I look at it I could definitely use some more depth.