Riddle me this! Turn on the heater, the motor overheats!

I have a 39 Chevy w/sbc 350, 4bbl, auto. It has a Vintage Air/Heater combo. I turn on the heater and get nice warm air. The temp gauge goes down a few degrees then climbs rapidly up past 250 then in a minute or two will come back down to about 225/230 then creep back up. It stays hot but I'm not sensing any clatter or difference in the engine running.

I turn off the heater, it drops back to normal ~ 200 or just below. I have a 193 thermostat. This outside temp in in the 40's and this happens on the freeway or around town. Of course, I've checked all the obvious, coolant level, collapsed hose, loose temp wire connection.

I'm thinking I must be loosing circulation in the left front of the intake manifold where the coolant sensor is located. I have a Edelbrock RPM Airgap manifold that I pulled, cleaned and resealed to fix an oil leak last summer so I'm pretty sure the passages are clear.

Any Ideas?

signed, warm but confused

 

add coolant....

 

Do you have any valves in the heater hoses ?

 

Not sure what your cooling system is like but if your radiator fill is not the highest point then you need a bleeder screw to vent the air out and probably add some more coolant. I bought an inline Moroso setup from the local roundy-round racer supply that fits in the upper hose with a pressure cap and overflow connection. I was able to add another gallon of coolant.

 

Air in the system. Get it out. It's the enemy.

 

Vortec engine ? Many have reported fluctuating temp. gage readings , some have installed a bypass from under the thermostat to the pump , in fact GMPP is also recommending it . Some have drilled the thermostat with 1/8" holes and still another was to move the temp. sender to the side of the left hand cyl. head and reported normal temps.

 

Is it possible there is some sort of bad earth on the temp gauge or a connection between earths on the heater and temp gauge? As you say it doesn't spit water or boil so maybe it's just numbers and not actual temp. Have you tried an infrared digital temp gauge to point at the radiator and heads to get a comparison?

 

What Snaptwo said; All temp senders need to be fully immersed in the coolant at all times, to work correctly. That includes the temp switches for electric fans.

4TTRUK

 

Do you have an electric fan on the radiator? Does it just operate off a temp switch or is it somehow wired into the Vintage Air controls? Maybe it's supposed to come on or increase speed any time the heater or A/C are switched on but isn't for some reason.

Strange symptoms... running the heater usually drops temps a bit. As mentioned already make sure there's no air trapped in the system.

 

Get the air out of the system as others mentioned. In the future, drill a small (< 1/8") diameter hole in the t-stat flange when installing it. This lets air escape as you fill the system.

 

Is the return line near the sender ? So that when the blower fan blows across the heater core it is also cooling the water back to intake ,if the return is close to the sender & could this be why the temp goes up and down when the heater is on ??

 

Thanks to all for you comments. I am suspicious there may be air in the system also. The coolant is up to the top of the radiator. The heater valve is a vacuum operated 4 way valve in the heater hoses and is apparently operating fine because the heater produces warm air when it on. I know the electric fan is running. I've been wanting a digital laser temp gauge so now I have an excuse to get one. It's a good idea to find out what areas of the manifold and radiator are hot and what areas are not. I'll report back what I find.
Thanks again.

 

Looking at the car, I bet the heater unit is higher than the motor, and maybe even higher than the top tank of the radiator. If that is the case, I'm betting trapped air in the system.

 

The vacume controlled inline valve being open has everything to do with the problem.
I'd suspect air also, however you'd think it would eventually purge itself.

 

Go get yourself a funnel that connects to the radiator cap outlet. Let it run with the heat all the way up, get it up to operating temp, and give the throttle a few quick cracks. To me it sounds like you have air in the system. By cracking the throttle a few times, you should be able to create enough turbulence in the system to push any trapped air out. I run in to this problem a lot with cars at my shop, mostly Mercedes and Infinity. But it's the same theory.

http://www.amazon.com/Lisle-24610-Spill-Free-Funnel/dp/B001A4EAV0

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Nataccountguy, (whatever that means)

I am not intimate with the plumbing arrangement on the SBC and naturally being a transplanted engine into a custom rod it is hard to say where your supply and return have been picked up for your heater.

Having said that, it sounds like your heater is returning to the thermostat and affecting it's operation by dumping cold water on it, Heater returns would normally return to the water pump or radiator on the suction side. Trace your plumbing and recheck your heater installation directions to be sure it is plumbed correctly.

TexasJohn

 

If the above doesn't work, you could always vacuum the system. There's a tool to do it. It attaches to an air hose. You vacuum it, then let it suck the fluid back into it to relieve the negative pressure.

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and so a... you could check it DEAD cold 1st thing in the morning, and see
if it is ... at all low.... then leave the cap OFF and start run, and check the warmth
of fluid as it warms UP.

get some special help and have them dial / rev up OH! so slowly
with the cap off (and you up there checking), to watch the flow and keep on checking the heat,
--- almost lost track---
when it is revved up and the (if ) fluid goes down...
and or completely disappears it is LOW as so many others have diagnosed .

now heres the trickie part when the engine returns to your normal idle
it will re-appear to be full... so you need to hold the RPM up and fill it at the SAME time and THEN cap it while its revved up.

Oh ya keep the heater ON fullblast

good luck
let us know the FINAL answer/solution .

 

At the shop I work at, the techs will bleed new cars with the front end up in the air (on an alignment rack's ramp, usually). This gets the radiator higher than the rest.

Might be worth a try.

Cosmo

 

I have had to do this a few times. Works pretty good

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I like the feed back and it is definitely sending me in the direction of trapped air and to find a way to bleed it. I will also follow the other suggestion to check the heater hose to see if it's dumping cooler water close to the thermostat and affecting it's operation.

Thanks all

 

A few pictures of "under the hood" might help us help you....

 

The kit is on ebay for about 40 $. Look up coolant vacuum refill kit. It takes about 5 minutes & will take out all trapped air from the system.!

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Well I'm back after a weekend trying to track down the mysterious cause of the engine temperature going UP when the heater is turned on.

Bottom line, I didn't find any problem with the cooling or heating systems.

I drained the system, pulled and replaced the thermostat water neck (was corroded and had a slow leak), used the opportunity to check the thermostat for crud or obstructions, pulled and checked the temp gauge sensor (yes it immersed in water), wiring is good. Pulled both upper lower radiator hoses to check for problems. Removed and checked the 4 way heater valve operation and the flow direction of all 4 water lines.

Refilled the system with the heater on full and the engine running. After a test drive to get everything hot I pulled back in the garage, carefully removed the radiator cap and let it run 3/4 hr with the cap off. There were random bubbles and the antifreeze level would slowly go down so I kept topping off. Hoping this would let any trapped air work it's way out. Once it quit bubbling the level stopped dropping.

I loosened the two temp sensors on the intake manifold to let out any air that might be trapped there. The heater core is higher than the motor but there is no way to bleed air out of it. Also, it heats well, so I'm not thinking there is any significant air in the core.

We took a long Sunday afternoon drive around the city with lots of stop and go and some 70 mph+ freeway driving. The weather was warm so we ran the A/C quite a bit. The engine is not overheating. I have a 193 degree thermostat and it runs right at 200. Sitting at long lights or creeping around a neighborhood with the AC on it will warm up to ~ 220 or 225. As soon as your back to driving speed its right back to 200.

Turn on the heater this morning on the way to work the temp immediately cools down to about ~180 then started crawling back up and away it goes all the way past the 250 mark on the gauge. In a couple of minutes is come back under 250 hovering around 240 or so then back up and stays above 250. The heater is putting out good very warm air. After 5 minutes or so I cut off the heater and the temp comes right back down to 200 and stays.

I called tech support at Vintage Air and it'a a mystery to them. Although I did find out the 4 way heater valve is not theirs.

I think I'll replace the 4-way valve with a plain off/on valve in the line between the manifold and the heater core.

Sorry for the long winded reply

 

Why do you need a valve anyway?
All your description points directly at it being the cause, what or why it's giving you trouble I have no idea.

 

Where are your supply and return lines connected?

 

Just trying to think of some other quick tests you could try.

How about taking the heater core out of the circuit? Disconnect the hoses at the heater core and shunt them together, leaving the heater valve in place. Then maybe also try bypassing the heater valve as well by connecting the two hoses together that connect the engine to the valve. See if either of these combinations give you any different results.

 

Well if its a 4 way, there's a lot of different options right? And there's not a clear indication of what routing to follow because it hasn't been identified at least not by vintage so their instruction could be wrong for the valve.

 

Good idea.

I also agree with drilling a small 1/8" hole in the thermostat. I do that on all my cars. Also, make sure no hoses are higher than the radiator cap.

I also like to get full vacuum advance at idle (I hook it up to a full time source) - helps the motor to run cooler

 

Get an infrared thermometer and check the temp of the radiator while it is "overheating". It may not be. You may have a wiring/ground issue that is causing it to appear to be overheating while the heater is on.