Thread: Overheating Mystery

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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.

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?

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.

Originally Posted by MP&C

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

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

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.

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!

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?

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.

Originally Posted by shine

looks like the rad is full of stopleak .

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

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.

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.