Weird temp issue

[Chevy nutcase]

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.

[caseyjones]

Any chance you ended up with a reverse-rotation fan on it? Derale makes them. I suppose for the serpentine reverse-rotation setups.

[Chevy nutcase]

Originally Posted by caseyjones

Any chance you ended up with a reverse-rotation fan on it? Derale makes them. I suppose for the serpentine reverse-rotation setups.

No the fan blows really well but I think the clutch I purchased is either faulty or reverse because it's always engaged. I took a chance on it from summit because it didn't specify which rotation it was so other than wasting $40 it's not the problem

[cwcarpenter98]

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?

[Chevy nutcase]

Originally Posted by cwcarpenter98

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?

I do have the original 4 blade direct fan that I can put back on. As for the lower radiator hose I know it does have the internal coil in the bend but I'll have to see if the rest of ot has become doughy

[JPBrecheisen]

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.

[Chevy nutcase]

Originally Posted by JPBrecheisen

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.

How would one determine if the outer portion of the balancer has slipped? Is the timing mark aligned with the key?

[JPBrecheisen]

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

[Wrenchbender Ret]

Try another therm. About half of them are defective.

George

[cwcarpenter98]

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

[JPBrecheisen]

Originally Posted by cwcarpenter98

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

Had similar experiences with this.

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.

[geezer#99]

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.

[Chevy nutcase]

Originally Posted by geezer#99

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.

Yes I have the line to the overflow tank cap that has a pickup tube extending to the bottom. As for the heater hoses, they are two different sizes, one us maybe 3/4 and the other is 5/8 I believe and go back to the thermostat housing and pump and given the size difference can't be crossed easily

[shp4man]

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.

[Chevy nutcase]

Originally Posted by shp4man

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.

I have used the infrared to determine what my C-H temperature gage was telling me. I hit the water neck leaving the engine right above the thermostat and temp sensor. When the gage is in the middle its running 180°-185° where I like it. If the needle hit the H its up to 200°-210°. Since adjusting timing the temps are behaving much better but if there was one thing I'd like to add is a full shroud which I'll have to fab myself.

[geezer#99]

Here’s a cheap shroud to experiment with.


https://www.speedwaymotors.com/Speed...SABEgIqNfD_BwE