Could my AC be overheating my truck?

[davepl]

Short story: on a hot day (>80), at idle, with the AC on max, my stock 402 truck cannot hold its temp at the thermostat point of 180. It creeps up to at least 200+ and really seems like it'd go forever if I didn't intervene. That takes half an hour though, it's not fast. So traffic jams and parades are a problem. But I bet from the factory you could do it.

I put a SPAL 12" pusher fan in between the condenser and radiator yesterday and it comes on at 195 and helps somewhat. It seems to help the engine stay right at 200 or so, but if I had more time maybe it'd still creep up, I don't know. It was a significant improvement but not a "fix".

What stymies me is that this truck is totally stock and totally restored. New rad, new GM clutch fan, proper shroud, etc. There are two things it's fighting:

- Even fully warmed up there's more exhaust coming out of the driver's side, so the crossover is still bouncing closed, forcing hot exhaust through the intake manifold. I could wire it open for summer, but they didn't have to stock.

- With the AC off it'll idle at 175F all day.

So the AC thing made me wonder "Well how hot is the air coming off the condenser" and the question is "too hot to touch". You can't touch the condenser, it's literally that hot.

So that's the one thing that's different - R134A and a parallel flow condenser. And it DOES rock the cold air in the cab very nicely and freezing cold. So I'm wondering if the AC system is maybe moving more heat than it would have stock, due to the parallel flow condenser, and that's causing it to have trouble cooling the engine at idle?

Thoughts?

[toolboxchev]

I realize your pain. Yesterday was hot and my truck also ran over normal as expected.

I have a new cooling system with a 165 thermostat ( stant premium stainless product ) and I am getting ready to change out my water pump again. Stant makes those thermostats in 2 different product lines. A Radiator guy here locally pointed out to me those low budget ones have a high defect rate and they stick quite frequently. I am thinking of a Mr Gasket high flow unit when I do the next rebuild.

The stock unit ( water pump ) has a cast impeller. I upgraded to a new unit with a stamped steel impeller which is supposed to have more flow. As I remember over 10 years ago the cooling system had this style of impeller in the pump and I did quite well keeping cool. This unit I have on now does nothing for helping out on the hot days.

Last summer I completely rebuild the cooling system yet kept that crappy water pump on it since it was only 6 months old. My system was acting like a heat sink, when it got above 80 it would continue to heat up driving me nuts, yet on a cool day it would have no problems.

How much do you drive your rig in summer? I would venture to say you use it a lot during this time of year.

Thanks again for the help with the Front End components still having a bear of time removing that last lower ball joint but I will get it!!!

Hope this helps

[harpo231]

Could be compressor,water pump,or glogged fins in condensor radiator if only when ac is on.

[weq92f]

Sounds like your AC is overheating your cooling system.

If you're not seeing a rise in vent temp at idle over time, the condenser has good flow, which means all the heat is being pushed/pulled through your radiator. Add the load from the pump and you've got all the potential for a problem.

Have you checked your clutch fan under heat/load? When it heats up past it's 'target or engagement' temp, it's supposed to become rigid and pull more air.

When it gets to 200+, just kill the motor and watch the fan. If it doesn't stop real fast with the engine, you need a different clutch.

-klb

[67ChevyRedneck]

You can also give it a "flick" when it's hot. It should barely move. You should be able to notice it moves much easier when flicked "cold".

I have a 195 Thermostat in my truck. It was 96* here on saturday. I had the A/C cranked on high for an hour+ on the interstate and in traffic. My truck will run 200-205 on the interstate when it's that hot out and about the same in traffic, it might get close to 210, but it will come back down, go up, back down, etc. I also have a 700R4 adding heat to the radiator.

I have mine set up with all GM stuff too, with a 4 row radiator and correct clutch fan and shroud.

I don't know much about the larger GM engines, but I seem to recall they all ran a little on the warm side (hence the giant radiator you always see in BB vehicles)?

215-220 should be safe enough range to let the truck get hot. I'd verify that it really is going past the 210 mark before freaking out and swapping parts.

[FirstOwner69]

I am not a mechanic, nor I am not an expert. What I'm going to say may start a huge debate.

I do not consider 210 degrees "over heating". I call that "running hot". A system with a 15# cap and 50% ethylene glycol will not boil until it reaches 265*. Sometime during the 60s, GM vehicles changed to 195* thermostats primarily for emissions purposes. Simply stated, engines are supposed to run cleaner at higher temperatures (I imagine to a certain point). I've had 4 later model Chevy pickups (a 1986 dually with a 454 and 3 Duramax duallies). I have towed heavy loads up steep grades with all of them. The auxiliary fans never kick on until the gauge is at 210*.

Are you still running an A6 compressor? If so they place a higher load on the engine than the Pro10 replacements or the more modern compressors. A temperature rise is normal., certainly at idle. I wouldn't be too concerned about higher temps, say 210* or below, unless they are routine when driving at highway speeds.

Let the debate begin!

[cleszkie]

If your pusher fan is trying to move more air than your mechanical puller fan is pulling over the area that your pusher fan covers, then the pusher fan is not operating at its full efficiency. It is basically dead-heading against the slower puller fan flow. I would try moving your pusher fan to the other side of your condenser. That is where I have mine mounted. That way, the pusher fan can operate at full efficiency, regardless of the puller fan flow rate. The excess flow from the pusher fan going through the condensor will just bypass the radiator by escaping through the gap between the condenser and radiator.

[engineer_gregh]

Dave I feel your pain. I upgraded my cooling system with a Griffin Radiator and two 1600 cfm fans because I get very uncomfortable with my 402 approaching the 200 degree range. It did fix the problem, never ran hotter than 195 degrees even in Nashville with 80-90% humidity and 95+ degree temp. The Griffin radiator was not reliable, its an epoxied versus welded radiator. I'm now back to my original 4 row brass but with the aluminum shroud and electric fans I was running on the Griffin. My AC is down at the moment so I can't say for sure if the electric fans with the brass 4 row will work. I'll let you know if a couple of weeks as I'll have rebuilt the AC by then. I've been told numerous times that even when these trucks were new, the big blocks would run up to 3/4 of the gauge with the ac on in traffic in hot weather.

[cleszkie]

I should note that I run dual electric puller fans with a full shroud on a fully welded BeCool 2-row aluminum radiator. I also ditched my heat generating auto tranny for a manual. With Vintage Air A/C running, sitting in southern California traffic, or pulling a mountain grade, temps never get over 195 degrees.

I would tend to agree that seeing temps into the low 200's while running the A/C, with all of the stock cooling gear in place, isn't out of the ordinary, and isn't particularly harmful to the engine. That's just the price to pay for staying true to the stock equipment.

[Stocker]

Originally Posted by FirstOwner69

I am not a mechanic, nor I am not an expert. What I'm going to say may start a huge debate.

I do not consider 210 degrees "over heating". I call that "running hot". A system with a 15# cap and 50% ethylene glycol will not boil until it reaches 265*. Sometime during the 60s, GM vehicles changed to 195* thermostats primarily for emissions purposes.

Originally Posted by cleszkie

I would tend to agree that seeing temps into the low 200's while running the A/C, with all of the stock cooling gear in place, isn't out of the ordinary, and isn't particularly harmful to the engine. That's just the price to pay for staying true to the stock equipment.

You won't get a debate from me, in fact you both said pretty much what I was thinking as I was reading the thread.

210* is starting to get warm but is nowhere near overheating in a sealed, pressurized system containing 50% coolant mix.
Yes, A/C will naturally add heat which will raise the coolant temp. I do not see a problem here.

[CST10]

When I added a vintage AC system to my 462 CI C10, the temperature rose from 190 degrees to 210 degrees and also seemed like it wasn't going to stop.

I ran a test, idling in gear with E brake on and no AC in 95 degree boiling sun the truck ran between 190-195 for at least 20 minutes.

Same test but with AC on, it ran between 210-215 degrees. Where it would have stopped, I don't know but I turned it off at 215. Took out the temp gun while idling and the condenser was running 150 degrees........that's 55 degrees hotter than the ambient temp at the time. That kind of explains what was happening to my system. The radiator was seeing a 150 degree intake vs 95 degrees which caused it to heat up.

I added a 12" 1600 CFM pusher fan to the front of the condenser on the drivers side with an under dash switch. When the temp rises to 205, I turn it on and it will hold the temperature to 210 degrees for awhile.

Now my 68 with no AC and the stock 250CI and manual tranny runs at 200-205 with that little dinky 4 blade fan and factory no shroud set up.

Just sayin that you may have nothing to worry about.

[davepl]

Originally Posted by Stocker

You won't get a debate from me, in fact you both said pretty much what I was thinking as I was reading the thread.

210* is starting to get warm but is nowhere near overheating in a sealed, pressurized system containing 50% coolant mix.
Yes, A/C will naturally add heat which will raise the coolant temp. I do not see a problem here.

I know it's semantics, but I define overheating as "producing more heat than the cooling system can shed", which is the problem. I wouldn't mind if it went to 215F and stayed there (which it seems to do with the AUX fan so far) but the unbounded climbing is the problem.

Back to semantics, I never said it boiled over, of course. I don't think 215F is a problem in and of itself either, if the thermostat were a 210. But it's a 180F, and it shouldn't be running that far "out of control" of the t-stat in my opinion.

[FirstOwner69]

Originally Posted by davepl

I know it's semantics, but I define overheating as "producing more heat than the cooling system can shed", which is the problem. I wouldn't mind if it went to 215F and stayed there (which it seems to do with the AUX fan so far) but the unbounded climbing is the problem.

Back to semantics, I never said it boiled over, of course. I don't think 215F is a problem in and of itself either, if the thermostat were a 210. But it's a 180F, and it shouldn't be running that far "out of control" of the t-stat in my opinion.

In normal driving I doubt you are "producing more heat than the cooling system can shed". You will probably be running warmer than without the A/C on, but it should stabilize at a safe level. You probably have to consider how often you get stuck in traffic for long periods of time.

[Andy4639]

AC rule of thumb.

Keeping the evperator as cool as you can is your best friend no matter what! The hotter the eveperator gets the less cooling inside the truck gets. This also puts the pressure inside the ac lines at max that can blow a line are even bog down the compressor which in turn will take more power to run the motor which makes more heat in the engine bay. I think you need a bigger fan to begin with. I would get at least a 2000CFM fan and put it inside the shroud and pull the air through for a better cooling effect. You should have room to do this without hitting the clutch fan.

[clay68c10]

More fan will definitely help. My old 68 454 truck would run at 205 all summer long in Dallas with the a/c on, in traffic for extended periods of time.
I was running a stock 4 core radiator and the stock condenser with 134. I had a Lincoln MK8 electric fan with a PWM controller. Worth every penny.
I did a heat soak test once, it was 105 and I just got off the highway with the ac on. Shut the engine off and watched the temp peak out at 240. I started it up, idled with the ac on, and it steadily dropped back down to 205 in a couple of minutes.
That fan could move ALOT of air at full blast.

[Andy4639]

I had just finished posting this thread when I read yours last night. This is what I did. I used a Windstar van fan and it to is a heck of a air mover at 2600CFM on high setting. It's two speed also and the video is on low.

http://67-72chevytrucks.com/vboard/s...d.php?t=738555