The Stovebolt Site Forums The Shop Area Engine Shop Dumb question- engine overheats when idling but fine when driving

48 3100 with a 235 engine.

Engine overheats when idling but returns to 180 degrees when moving.

Could my fan blade be on backwards?
Could I have air behind the thermostat?
Or what else could it be?

Thanks

With the truck running at a high idle take a piece of newspaper and see if it sucks to the front of the radiator. If it does your fan is on right. Take the radiator cap off and run it up to temp and see if the water boils out or the level drops. Do this with your heater on if you have one. Top up the coolant to the proper level and put the cap back on. If the above doesn't fix it try checking the timing. Post back and let us know. More will chime in I'm sure.

Hi Martin. Thank you.

I will do as you suggested. My timing is fine. That's why I asked about the thermostat and air behind it.

80 degrees is hot here in SoCal and I don't believe that is hot enough for this truck to overheat at idle.

Thanks again

Don't you have a short shaft pump on that truck, or am I thinking of some one else?

What year 235 are you running? If it's a '55-'62, the water pump sit much lower that the earlier 216 and 235 engines. That will make the fan sit too low on the radiator if it's still in the stock location, which can prevent it from pulling enough air through the radiator.

Check the basics.

Fan belt tension.

Does the radiator feel the same temperature across the core?

A partially blocked core can restrict flow enough so that at idle it will not be able to cool the engine enough.

Where at higher RPM it makes up faster water pump operation and more air flow through the radiator allows the cooling system to compensate for a bad radiator.

How hot does it get? Does t boil over?

What I'm running is a 60 235 in my 48 3100. I installed the modification plate and have the original 216 water pump. The plate places it higher in the correct location. My flywheel is the smaller 216 one. I do have the larger 235 flywheel but believe the instructions said to stay with the smal 216 flywheel or the water pump will turn too fast. As for the thermostat I bought a fail safe 180 yesterday and will install it. I question everything now and don't want it backwards. I believe the spring goes down, into the engine block.

Thanks for your help. I'm confused and want this fixed. This is my daily driver.

Dennis, the pointy end of the thermostat goes up and the spring/button end goes down. Hope you get it sorted out.

Thermostat spring goes down.
If it does not overheat when driving I would say it is not trapped air.
When was the last time the radiator was flow tested?
With my adapter you should not have any over heating problems.
I get reports from people in the desert even running air conditioning with no overhearing problems.
Retarded ignition timing can also cause overheating. Don't trust timing marks.

I like the way this setup and like the adapter. No complaints there.

So, timing. Can you give me an easy way to check/ correct the timing. I thought it was right but if I'm wrong then I am eager to learn the correct way. Maybe this can be helpful to others.

Thanks again to all.

Another question. I wanted to stay 6 volts so I am using a 216 flywheel and starter. Does this impact any of this discussion?

I will check the octane mark at the distributor base and flywheel ball marking with needle on cover.

Thanks again

An idea? Do these trucks operate at 180 degrees while moving but, when stopped and idling, operate at a higher (200 degrees) temperature? Have you noticed this?

Just wondering. Thanks

By "flywheel" I assume you mean the crankshaft pulley? The 235 pulley is larger diameter, and might cause pump cavitation at highway speed, but it probably wouldn't cause any problems at idle. Try an infra-red thermometer aimed at various areas of the radiator to see if you've got spots that aren't doing enough heat transfer. If you're not using the 216-style water pump it's possible the position of the fan and/or the fan diameter might be part of the problem.

If it's not boiling over, it's not overheating.
Jerry

Mine stays about 180 ish when driving around at a good speed. When i hit stop and go it will climb to the 200 mark. I still have the lower water pump installed and have not changed it over yet. Never did actually overheat to date but this last weekend it took all of 1.5 hours to install a electric fan on a manual switch so i never have to worry about overheating.

Used a pusher fan on the front of the rad and put a switch in the cab. Tested it out yesterday in traffic and wow does it ever cool down fast. It was back down to 180ish in no time after being at 200 and stayed that way in traffic. All the parts came to $160cdn (16" fan, painless relay kit, spare cooler fan install kit, and a sexy s.s. press button switch)

I should have taken some pictures

My grumpy turned to something stupid.

OK, I have been trying to solve this grumpy overheating. And I was worried. I'm still unclear where overheat does happen or the temperature rises, and is alright. Wolffcub seems to have the same situation as I do. So, these trucks will stay at 180 degrees while moving and when stopped and being cooled by the fan - rise to 200 degrees. I got nervous at this increase.

Well, now it's stupid and I feel that way. I checked my fan belt this morning and there was a good amount of play. I tightened it and today I did not experience the rise in temperature but will keep an eye on it.

I will chalk this up to converting my truck to my daily driver and over reacting. I do hope this resolves this issue. Now on to that darn slow starting.
Thanks to all.

I hope that does it!
As far as timing, I like to advance the timing until max idle speed is reached, then retard it until the RPM's just start to come down.
This is a good starting point. After that make sure it does not ping, or kick back against the starter. If it does retard slightly more.

I like to know about timing the truck. I thank you for that.

I will assume your advice does not use a timing light which would be nice since I run a 6 volt system. My truck does run well. Advancing the timing (I assume is clockwise) then retard (I assume is counter-clockwise) until RPMs come down.

Again, I thank you and all others for your help. This is very important to me.

Looking at the top of the distributor, turning it CCW advances the timing. CW is the retard direction. You can use a timing light on 6 volt systems, just use a 12V battery to power the light and trigger the flash from either the #1 or #6 plug wire. The ball and pointer will align no matter which one of those cylinders you use as a trigger point. My Snap-on timing light will also show how many degrees of advance the centrifugal and/or the vacuum advance provides so I can check initial, centrifugal, and vacuum advance to get a total picture of the timing system. A delay-flash timing light is well worth the investment!
Jerry

Thank you Jerry. What I use is an old Sears timing light on the 6 volt battery. The flash is not as bright but visible. I should look into a better one that will work on 6 volts or convert over to 12 volts. I just like the idea of original.

Thank you for setting me straight on the clockwise - counterclockwise issue. I was backwards.

Dennis, as Jerry suggested you can use a 12 volt battery on your old Sears Timing Light. The battery from another car, your riding mower battery any 12 volt will do. It doesn't have to be in your truck just set it on a fender cover and hook up the pos/neg leads of the timing light and hook the pick-up as Jerry said to 1 or 6 and fire her up. Light should be as bright as new. Good luck.