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Weird temp issue
Had my 66 out today after thoroughly flushing the system and adding an overflow tank to eliminate trapped air and I still have a somewhat high temp issue that's been pestering me since I got my temp gage working. It's a bone stock 250 with what I'm assuming is an original Harrison radiator and the odd thing is the temp is fine putting around in traffic but as soon as i get on a stretch where I can maintain 50+ mph the gage creeps to nearly pegging the temp gage. I used a laser thermometer on the engine water neck and get an acceptable 185° when the gage is in the middle where I like it. When it tops out it's reading 200°- 210°. The only things I've done to the cooling system since I've owned it was adding a clutch fan, changing the thermostat to a 165° when I completely stripped the motor to clean and paint it and in doing so had the water pump off and thought it was fine and of course flushing it with the type you leave in and drive around for a few miles. I read on other posts about adding a front air dam because at higher speeds a low pressure bubble forms in the engine bay not allowing air in through the radiator. I will probably do this regardless but the truck has existed for nearly 60 years without one. Love to hear your thoughts.
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Any chance you ended up with a reverse-rotation fan on it? Derale makes them. I suppose for the serpentine reverse-rotation setups.
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If you still have the old fan, run it without the clutch fan to see if there's a difference. That can at least rule out the fan if there's no change.
Maybe you have a lower radiator hose collapsing at highway speeds? |
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Try another therm. About half of them are defective.
George |
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The radiator tubes might be closed up or the fins are not attached to the tubes. I had flushed a hot running engine before also but when I had the radiator worked on half the tubes were still plugged with scale. Guy tried to rod it but couldn't get it right so had to re-core it.
You might also check timing. Late ignition timing can make a motor overheat because it cooks the exhaust valves and the coolant does what it's supposed to and takes the heat away, thus higher water temperature. My guess is that it's more related to the radiator than the fan. I live in a rural area and I've run several of them without a fan at all without issues going down the road. There is sufficient airflow at even relatively low speeds to keep them cool. Double check the timing and make sure your damper hasn't slipped or is loose on the keyway. Saw that happen with a friends 250 I6 before. Lastly I'll mention fuel mixture. Lean conditions.(vacuum leaks) will also make them run a little hot sometimes. Just a few other things you might consider checking. |
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I can't say for sure about the relationship between the keyway and the timing mark on the damper but you could check it by doing this:
Take the No.1 plug out (removing them all will make the engine roll over by hand easier) and turn the engine over in its normal rotation until you see the intake valve for No.1 close and a bit further until the piston is at the very top of its stroke. This may take a few tries to get it perfectly at the top. A nice bright pen light should allow you to see the the piston through the spark plug hole as you do this. With the No.1 piston at Top Dead Center/ Upper Dead Center, the mark/line on the outer portion of the damper should be aligned with "0" on your timing scale. If it is not, there may be an issue with the outer damper. If the key way is wasted you would be able to rotate it back and forth a few degrees with the belt off. If you can't "rock rotate" it back and forth on the crank nose, the key way is probably fine. The one dealt with tuned back and forth without movement of the crank. Jonathon |
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More advanced timing will make them run good.
With ethanol blended fuels, you can probably run a few extra degrees of advance without hurting anything. If it is having trouble starting, you might have a tad much timing in it. Maybe back it off a tad to find the sweet spot. I will typically run timing where the shop manuals say, but most of my stuff is stock, points ignition included. Some will just advance timing at idle until the engine starts sputtering then back off a smidge and lock it down. Others will creep it in until it pings under heavy acceleration then back or off a tad. Advanced timing brings some spirit back into a tired engine. Just be careful not to do too much because it can cause problems under full advance (high RPM) conditions. Maybe back it off a third of what you put in and see if it starts better. When I helped my friend with his 250, that's what we did. I balanced the timing between idle misfiring and starting manners until we found a spot where it ran favorably in all places until he could make repairs. 200° isn't terrible temps for an engine if it stays there. Sounds at least like you're gaining on the problem. Don't count that radiator out though as you play with it. It's important to remember that even though the thermostat opens at its set temperature, it's the efficiency of the heat exchanger (radiator) that determines how much heat being generated by combustion than can be disapated into the air. If the radiator is faulty, a cooler thermostat will just make it take longer to end up at the temperature the radiator can effectively disapate. If the radiator was perfect (exchanging heat at same or faster rate than it's being generated) you'd probably run at 165° all the time. My the plugged radiator i mentioned previously had the symptoms you describe. Mine was a combination of late timing, a dirty block, and restricted radiator. Good luck Jonathon |
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I got quoted $400 to re-core my radiator about 7 years ago. At the time, a new aluminum was $200. I went with the aluminum because of the cost. However, as I have changed things under the hood to be more original looking, part of me wishes I had gone the re-core route. Too late now though!
I will say the Champion radiator I bought has worked great over the past 7 years. Doesn't even care that I've added a/c now either |
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On your air pocket theory, let it run until the thermostat opens then unbolt the heater and hold it down low beside the engine for few minutes to make sure all the air is out of the heater core. I had a 65 that I had to flush the heater core by itself then do this to bleed all the air out of it. The high mount cores can trap a little air because they're above the radiator cap. |
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Like you, I accepted functionality over form. I know copper/brass ones are reproduced for some applications but I wonder what the quality would be. That and they're quite costly. |
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I could easily fab a piece of 1/2" copper tube with a female fitting brazed on to accept this bleeder that ironically says "auto vent". Attach it in line up high near the heater core run it till I get the air out, remove the bleeder and plug the piece of tubing. Sounds jenky but if it works then :metal: |
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Is your overflow tank set up to return coolant to the rad when it cools down?
Do you have the heater hoses hooked up right? Thermo housing to bottom of heat core, top of heat core back to water pump or rad is normal. |
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Modern replacement temp senders are incompatible with the old temp gauge. Sounds like you have an infrared temp sensor. Shoot it and make sure it's actually overheating before you spend a bunch more money.
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