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Old 04-05-2022, 08:10 PM
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Default Overheating!! - Troubleshooting not going well

little background, '72-400 .030, summit 2800 camshaft, 16 heads (9.75:1 CR)
running/breaking in on test stand at 2500 PM, new Champion radiator, electric fan w/ 180 degree T-stat.

fired up great, all vitals OK except for coolant temp rise to 230 within 10 minutes. initial timing at 16 BTC. removed T-stat and replaced it with gutted one and it will run about 15-20 minutes, but temp will climb to 230 fairly quick after warmup. i did remove the milodon aluminum water pump and adjusted the divider clearance to .010 to .015 clearance with no improvement. for reference, all components inside the timing cover are new- divider, sleeves, seals, etc. so i went to the sticky and copied the following and my best diagnosis as to the current conditions. any advice helpful.


;21 Reasons why your engine may run Hot.




*A lean air/Fuel Ratio (Also check fuel pump and Filter) - ELEC PUMP, NEW FILTER
*Too much timing/retarded timin/advanced curve malfunction -VARIED TIMING WITH NO SUCCESS
*Clogged Radiator/Collapsed Hose (restricted water flow) - NEW, NEW
*Clogged Engine (restricted water flow) - NEW REBUILD (CLEANED)
*Stuck Thermostat / Incorrect Thermostat - tested WITH, WITHOUT, AND GUTTED
*Bad Water Pump - NEW AND CLEARANCED
*Incorrect Water Pump Speed (too slow/too fast)- FACTORY PULLEYS

*Radiator Too Thick - SPEC'D FOR ENGINE (NEW) Champion
*Wrong Pressure Cap - 15#
*No Shroud Around Fan. Improper Fan Position Within Shroud. - ELEC FAN W/IN 1" OF RADIATOR, NO DIFF WHEN ADDING HIGH FLOW SHOP FAN
*Bad Fan Design - Stock Factory Type Usually Works Best. - NOT TESTED
*High Volume or High Pressure Oil Pump - NEW MELLING FACTORY SPEC PUMP (GOOD OIL PRESSURE)
*Electric Fan (Pullers/Pushers) Blocking Air Flow - (Puller) ADDING EXCESS AIR MADE NO DIFF
*Too Much Antifreeze - 50/50 BLEND
*Wrong Type Antifreeze - CORRECT
*Flow Test: Begin with cool engine. Remove radiator cap. Start engine. Bring engine up to operating temperature so that the thermostat opens. Increase engine speed to 2000 rpm. If water gushes out of radiator there is a flow restrictionin the system. This must be corrected for proper cooling. - NOT TESTED
*Wrong Spark Plugs (ie. Heat Range) HEAT RANGE "5" AS RECOMMENDED BY BUTLER
*Wrong Gasoline Type (Try 89 or 92 Octane) - 89 CURRENTLY
*Clogged Catalytic Converter. - NA
*Clogged Injector System. - NA
*Exhaust getting into the water due to a cracked head or blown head gasket. - SYSTEM HAS BEEN PRESSURE TESTED

Again, i am running the engine on my test stand with all necessary components connected. can supply pics if necessary.

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Old 04-05-2022, 09:22 PM
Murf Murf is online now
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First I’d verify that your gauge is correct. If it is, the first thing I would be suspicious of is the electric fan. I’ve not had good luck with them in the past.

Good luck!
Murf

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Old 04-05-2022, 09:56 PM
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I run this radiator in our 68 Firebird. https://www.griffinrad.com/inc_resul...model=Firebird

It has 2 rows for cooling that are 1.25 wide. No issues. Your initial timing is 16 deg. What is your total timing? All in by what rpm? The stock cast water pumps with cast iron impellers in my opinion are hard to beat. Also run the smaller pulley on the water pump. A 160 deg thermostat is fine also if driving in the summer.
Do you have you electric fans turning the proper way? Also, what kinda shield is on the radiator with the fans? Post some pics.

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Old 04-05-2022, 09:56 PM
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I had similar issues on my test stand. 2500rpm with fake air movement from my test stand electric fan wasn’t enough. 10min was about my limit too. I did my break-in over the course of 3 separate runs after cooling down. I also swapped my regular mechanical fan on it with a temp shroud around it.

I figured that even when the engine is in the car with air being ducted over/under/around the engine the way it was designed, I’d still be looking for trouble sitting still trying to hold 2500 for 30min. After break-in, idling on the stand was not as big deal temp-wise.

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Old 04-05-2022, 10:08 PM
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X2 above. The electric fan and lack of fan shroud are suspect. I know you’ve tested with a high speed shop fan, but that might not be enough. Also infrared thermometer on temp sender to verify gauge accuracy.

Some say that air pockets in the cooling system can cause overheating. When I’ve have had similar cooling gremlins with new/rebuilt engines they’ve eventually gone away after tinkering with the system and filling/refilling the coolant, which makes me think there may be something to that. Try filling the system with the heater hose (coming out of the head) disconnected, and then reattach the hose once coolant starts coming out of the hole. Also drill a couple of holes in the thermostat (assuming you’ve put it back on). Then when you start it up, turn the heater on full blast, and leave the radiator cap off, adding coolant as necessary. This should get any air out of the system.

The only other big factor that has worked for me in the past has been adjusting the initial timing. I see you’ve already tried that, but you may consider further investigation down that road, as it seems to have the most significant effect on overheating when everything else is ship shape.

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Old 04-05-2022, 10:09 PM
1965gp 1965gp is offline
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Do the electric fans have a shroud covering the rest of the radiator? I had the cold case fans and my GTO and it kept overheating. Took the shroud off and it helped dramatically. I went back to a clutch fan.

The shroud was blocking the air flow

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Old 04-06-2022, 07:06 AM
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Quote:
Originally Posted by 1965gp View Post
Do the electric fans have a shroud covering the rest of the radiator? I had the cold case fans and my GTO and it kept overheating. Took the shroud off and it helped dramatically. I went back to a clutch fan.

The shroud was blocking the air flow
This ^ a lot of the shrouds I’ve seen are too shallow & flat. Look like a baking sheet with a hole in the center. I don’t think the air can flow through & kinda stacks up in there.

Murf

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Old 04-06-2022, 10:11 AM
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Essentially the only airflow I was getting was two 14” circles- the rest was useless.

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Old 04-06-2022, 10:55 AM
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thanks for all replies. i did have reservations about the cooling fan/s and running a constant 25K RPM, but this isn't my first rebuild or first Pontiac rebuild (lotta Chevrolets) and have never had this issue before. i'm gonna install a factory shroud and mechanical fan next. the system has been burped of air and. new Moroso full flow T-stat is on the way.

Any other input is greatly appreciated.

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Old 04-06-2022, 11:19 AM
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Have you verified your timing marks are accurate? If the balancer has slipped, or is marked incorrectly, your timing may not be what you think it is. Retarded timing will make one run hot.

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Old 04-06-2022, 11:38 AM
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Quote:
Originally Posted by noalibi View Post
thanks for all replies. i did have reservations about the cooling fan/s and running a constant 25K RPM, but this isn't my first rebuild or first Pontiac rebuild (lotta Chevrolets) and have never had this issue before. i'm gonna install a factory shroud and mechanical fan next. the system has been burped of air and. new Moroso full flow T-stat is on the way.

Any other input is greatly appreciated.
I’d bet dollars to donuts your heating issue will suddenly go away.

Also 230 isn’t really “overheating” especially if your running a 15 lb or so cap.

Murf

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Old 04-06-2022, 12:25 PM
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Pontiac engines don't put enough cooling to the rear or middle if the blocks. Running fuel with Alcohol can make it even hotter.
The engineers designing the shroud and fan set up knew what they were doing.
The day I see a flat front air intake on a jet engine, I will use one. Seems air and water do NOT like a "wall" or sharp corners to go around. Funny how basic aerodynamics has been Ignored on cars, but Not on jets..or boats..

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Old 04-06-2022, 12:29 PM
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Want to have even heat through your block with no hot spots? Want the engine to run at the temp your t stat decides? Read the thread below on this page about running cooler started by Steve Barcak. There are pics and explanations.

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Old 04-06-2022, 08:55 PM
tjs72lemans tjs72lemans is offline
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Many good points here. But, I'm not sure how you can regulate the coolant flow with no thermostat. Even a 180 with a burp hole should work. I missed it if you mentioned it, but someone else did. A good fan in front blowing hard helps. I agree you have to verify temp with a temp gun.

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Old 04-08-2022, 05:33 AM
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Don't pull your thermostat. Hell, if you're past the thermostat set temp, you essentially don't have a thermostat, anymore, anyway since it's fully open and will stay that way if you're overheating.

Running at 2500 sitting still will require a lot of air movement to mimic highway ram air. With stock gearing and trans, that's around 60 MPH. One good electric fan I've heard positive feedback on is the Flex-A-Lite #295 (116524) with dual 13.5" fans. It pulls 4600 CFM of air, but more importantly the shroud for each of the fans is slightly conical like what is seen on most modern car fan shrouds, and so it's not perfectly flat up against the radiator core like the terrible Cold Case ones I've heard about.

Sounds like it's not a water flow problem, either. Your pump is clearanced, and a Milodon pump is a good pump.

Ultimately I think this is an air movement issue. Either upgrade to a better e-fan, or use a clutch and proper shroud.

And of course timing. 16 degrees initial should be plenty, though. Are you using vacuum advance to achieve good cruise timing? A V8 will happily cruise at that RPM (2500) from anywhere between 48-55 degrees total with vacuum advance added in.

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Old 04-08-2022, 10:19 AM
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I would suspect the fan(s). What fan setup do you have?

That #295 fan is hard to beat, as long as you have it properly wired and a good alt (and belt doesn't slip).

Is there a spring in the lower rad hose to prevent from collapsing?


.

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Old 04-10-2022, 02:30 PM
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My guesses are too little airflow, and a tight, fresh engine. Once some time has been put on it, it will loosen up a bit. Less friction, equals less heat.

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Old 04-11-2022, 07:44 PM
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haven't fired it in a few days...other priorities. as soon as i get enough run time, a full flow t-stat, and try a shroud/mech fan i'll know more. only have about 1 hour run time so far. i have an old crap quadra-jet on it now so that may be an issue too. will get a holley sniper efi when installed. i am also doing the rear heater hose Tee mod and a manual ball valve to regulate flow through the heater core based on Youtube's "Fast Monty's" testing results.

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Old 04-11-2022, 08:39 PM
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use a lazer thermometer and check the temp going out of the radiator and also going into the radiator.Should be a 30 degree drop.Tom

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Old 04-12-2022, 11:52 AM
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Quote:
Originally Posted by noalibi View Post
haven't fired it in a few days...other priorities. as soon as i get enough run time, a full flow t-stat, and try a shroud/mech fan i'll know more. only have about 1 hour run time so far. i have an old crap quadra-jet on it now so that may be an issue too. will get a holley sniper efi when installed. i am also doing the rear heater hose Tee mod and a manual ball valve to regulate flow through the heater core based on Youtube's "Fast Monty's" testing results.
What fan(s) are you running?


.

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