Technical Chevy 327 overheating mystery

Good point......yes I am sure the fan is running the right way.
Thanks

 

I think really the major change since the rebuild is the rust in the block, unless new-rebuild friction could be a factor. The engine has 1000 miles on it now, so it seems like any extra friction would be gone by now. I'm pretty sure they hot-tanked the block with something (acid?) and may not have rinsed it out well. When I left in my garage for 20 years before installing it in the car, I can see where moisture in the air and acid residue would work to develop rust in the cooling passages....and it may be significant based on the particles I have seen.....about the size of a #6 flat washer. I really wish I had known to rinse and treat those cooling passages at the time I stored it.

 

That's a very good question. I replaced the clutch just to be sure, but I was not able to verify that it changes with temperature. I read somewhere that you can test them by holding the fan still when the engine is cold, which I tried, but was not able to hold it. It seems to run and blow air at all times.

 

Thank you, that's a good piece of information. I tried to measure it last night, but was getting weird and inconsistent readings. I am going to change batteries in my IR thermometer and try again.

 

You sure the lower hose is not collapsing?

 

I have it on my list to double check for a spring in the hose next time I have the system drained. I know it is not collapsing at idle (when it is overheating) or at higher rpm in the driveway, but not sure about out driving.
Thanks

 

Don't need it drained, just squeeze it and see if it goes flat, not running, of course!

 

If the pulley on your water pump is too small the pump will cavitate and you'll not get enough flow. With the thermostat open you should see turbulence in the water at the radiator cap. As your radiator is uniform temp I would suggest you have a coolant flow problem. Another possible problem is that the bottom hose collapses because of the suction from the water pump.

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Myself , I would burp all the air out of the system , no help ,pull the head.

 

Good thought...….thanks

 

The pulley is original, so should be okay, but I hear what you say about flow. I am going to check at the cap for turbulence. Also double check my temperature readings of the fins and of the inlet/outlet hoses.....thanks.

 

Sailsman, I’ve followed this thread,there have been a lot of suggestions. I think you have a plugged radiator and should check It visibly or with a bore scope, mainly due your repeated references to big rust partials. But several photos of the engine, engine compartment, radiator, fans, etc, might help discover your problem. I saw the one very limited photo and saw a lot of hoses for a sbc. Can’t hurt anything. Just my .02.



Bones

 

Thank you Bones......your .02 is worth more than 2 cents. I was just sitting down to make a plan, and I think I will put the radiator first on the list.

Thanks to everyone who responded for their helpful comments. I will report back the final solution.

 

With that much rust floating around, is the thermostat plugged? BTW, what degree thermostat are you running anyway? Don't run without one (You'll start a thread war on here!)

I had a rusty block one time and I ended up taking the thermostat out (temporarily) and putting a nylon stocking in the top radiator hose (temporarily) to catch the rust flakes. It worked!

 

That would be the biggest thanks of all. You could be helping out a lot of folks by doing that.

 

My thermostat is 160*. I tested the old one and it was open at 170, so I replaced it with another 160, which ,when tested, also opened at 170*…..I called it close enough. Perhaps my thermometer was off.

I have since then had it out twice and there was no blockage (darn!). If there had been rust blockage, I may have removed the thermostat (temporarily ) to let it pass through. I like your idea of the nylon stocking....I think I may have seen it on this forum awhile back and ultimately found something called a Tefba filter that inserts into the top hose. It has its own pressure cap and a screen to clean out. It has caught some rust particles, but I fear most of them were already circulated into the radiator before I installed it.

 

Take the radiator out, turn it upside down and run a water hose into the bottom hose, (which is now on top) to back flush the rust out. You may be surprised at how much***** comes out this way.

 

Great idea. I think that is what I will do.....and inspect it with a borescope

 

I still maintain your block is full of sludge and needs cleaned .

 

And after doing that, remove the tanks and see how much MORE***** is removed. With pictures!

Ben

 

Corvette C3's are a real****** to keep cool

My race car was a Big Block c3 [1970] which is just a giant "heat soak".
A bigger radiator simply meant "a few extra laps before it started cooking".

In the end, we cut vent holes in the front apron above the front air-dam and sealed off the lower radiator,
We opened up the cowl induction behind the engine and removed the "egg-crates" from the fenders to bleed off hot air.
We also sealed off from 1/2 way up the grille to the top of the radiator with an internal dam.
All air from the lower grille half and apron vents went through the radiator and exited through the fenders and cowl.[even with a dry-sump tank in the path]
All air from the upper grille half, exited through vents in the L88 style hood [bleeding off pressure]

And All overheating issues disappeared [from sheetmetal work only]

Attached is a photo of the ducting that separated the grille

 

Try a 190* thermostat... You may not believe this, but it will stay very close to 190* and be much more consistent. Plus, the motor will run much better, last longer and the carburetion will be better.

My car only has room for a half a shroud and it did exactly what your car is doing. So, I changed the thermostat to 190* instead of 160* and it straightened out. (This will start a sh-- storm on here too.)

It keeps the water in the block long enough to transfer the heat into the water and in the radiator long enough to transfer the heat into air. The colder the thermostat the worse that situation becomes. Especially without a proper shroud and hot air excape!

 

Totally agree.
The OP should put a star next to this post.

 

Guys, we've been over this several times on different threads, that's not how the physics of heat transfer works. Besides that, once the thermostat is open it's open, the coolant cycles and the thermostat is not keeping the coolant in the block any longer. Sorry, but this is just FUD.

 

Here we go...

Besides that, once the thermostat is open it's open, the coolant cycles and the thermostat is not keeping the coolant in the block any longer.

And that is exactly why it eventually overheats. It takes time for the heat to transfer!

 

Take a piece of metal that you have welded or cut with a torch plunge it in a bucket of water and right back out. Then grab it with your hand you will remember it takes a while to cool.

 

This has been beat to death but is a total myth....some people refuse to accept it.

Since it seems to overheat under all conditions and not much has changed I’m with the flush the radiator crowd. Once again if it overheats going down the highway it’s not a fan or shroud issue.
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I'm gonna go watch The Big Bang Theory now!

 

Did you put a new water pump in when the motor was rebuilt. ?? check the number on the pump to verify that it is the right rotation pump. I found this problem on a past project .the car would overheat when driven on the freeway.

 

Think about it a little more. Once the thermostat is open (i.e. BEFORE the overheating occurs) the cycling of coolant takes place, the thermostat is then "out of the picture", it's not doing anything. Besides that, you're wrong about the coolant needing more time to transfer heat. Seriously, this has been beat to death, it's an urban myth that the science already has been explained on. Please stop repeating this FUD.