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.

Re: Weird temp issue
 

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

Re: Weird temp issue
 

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

Re: Weird temp issue
 

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?

Re: Weird temp issue
 

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

Re: Weird temp issue
 

Try another therm. About half of them are defective.

George

Re: Weird temp issue
 

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.

Re: Weird temp issue
 

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

Re: Weird temp issue
 

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

Re: Weird temp issue
 

Well I went and did some timing adjustments this morning. Plugged the vacuum advance line and timing light showed the mark dead center on the gage where it was when I switched to HEI. This time I put a vac tester on the manifold and at idle it was showing poor vacuum in the "latent timing" region. I twisted the dizzy counterclockwise, idle came up and so did the vacuum tester. Where the motor seemed happiest the timing mark on the damper is about 1" off the metal gage towards vertical. Backed the idle to 750 rpm and took it out for my typical 5 mile test run. It runs much better with better power and it doest spit at all between shifts like it did before when I drove a tad aggressive. The temp did stay lower longer but it did eventually creep back to 200°. To add it does start differently. Before with a little choke it would take off immediately, now it sounds like the starter is having more difficulty turning the engine once or twice before it takes off.

Re: Weird temp issue
 

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

Re: Weird temp issue
 

I was going to edit my previous message as the last one I wrote was sitting at a mini market which is my turn around point to let it cool for 10 minutes on these test runs. My trip home was much better as the temp gage never got to that H zone. The trip is about 3 miles of 50 - 60 mph and the rest is 2 miles of about 15 traffic lights. And after I let it cool down it had zero trouble starting so yes thank you I think I'm getting in the ballpark. I still think a rogue pocket of air is making the water pump stammer or the pump itself may need replacing. As for the rad itself I only ever knew of one shop that could recore a radiator and he retired long ago. This day and age I imagine if I could find someone to do it the price would easily rival a new aluminum replacement

Re: Weird temp issue
 

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

Re: Weird temp issue
 

Yes, radiator shops are hard to find and the cost of copper cores are ridiculous.

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.

Re: Weird temp issue
 

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.

Re: Weird temp issue
 

I was thinking there has to be a better way to bleed air off and I thought of one of these.

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:

Re: Weird temp issue
 

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.

Re: Weird temp issue
 

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

Re: Weird temp issue
 

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.

Re: Weird temp issue
 

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.

Re: Weird temp issue
 

Here’s a cheap shroud to experiment with.


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