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Getting hot at idle - what next?

AZ79K5Project

AZ79K5Project

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I’m not sure what else to do. At idle when the temperature approaches 100, the engine temp slowly creeps up. I shut it down at 215/216. It takes about 10 minutes to go from 180 to 215.

I have a small pusher fan I can turn on that drops the temperature to about a steady 200-205. So an airflow problem, right? But why.

I’m running:
Standard 350 iron block
MSD Atomic EFI - Idle - around 800
Summit heads
Mild cam
Edlebrock intake
Block hugging headers
Cold Case 34x17 radiator (two core - 1.25”)
High flow water pump (clockwise rotation - Edlebrock 8499 - I think)
180 thermostat
Full / tight fan shroud
Severe duty fan clutch
20” Derale mechanical fan
AC stays nice and cold so it’s pulling air without the aux fan

As soon as I start driving, the temperature drops and stays at 180.

I did swap to the serpentine (alternator) / V - belt combo for the AC/PS from the Pontiac but the pulley size should be the same (I think) from an all v-belt.

What am I missing?
Why is this getting so warm at idle?
Would a bigger radiator help? I could go to the 34x19.
Would going to a three core with small tubes change it? (.63 three core VS 1.25 two core)
 
I set it to 12 with the vacuum advance disconnected.

I’ve got it normally connected to manifold vacuum
 
Make sure the fins on the radiator are clear of mud/bugs. Also have your radiator cap pressure tested, if it leaks then it’ll overheat easier.
 
Can you drive the temp down at idle by increasing the RPM a bit? Should tell you if it's water pump speed related, or airflow based on vehicle movement. Cold AC means air IS moving, right?

To be honest I can't recall a setup where someone managed to "underdrive" a water pump. I suppose it's possible with the wrong combination of pulleys, but I have the same (general) setup of water pump/crank/alternator run off the ribbed belt, I can't imagine GM set those up with a multitude of pulley ratios. But it's possible I suppose.
 
rampage said:
Make sure the fins on the radiator are clear of mud/bugs. Also have your radiator cap pressure tested, if it leaks then it’ll overheat easier.
Click to expand...
I pulled the radiator and made sure the fins were straight and it was clean.
 
Try ported vacuum, above the throttle blades, and check idle mixture.
 
I’m running the MSD Atomic EFI. I just went through emission testing. I adjusted the loaded AFR and it passed. It was too rich under loaded conditions. The idle AFR is set at around 14:1.

My idle readings looked good for emission standards but maybe change the AFR to make it a little more rich?

E0F41EB5-880D-4383-94D9-1DB7BC136F77.jpeg
 
Which gases are those. Did it have the heating at idle before the adjustment?
 
Wes Harden said:
Which gases are those. Did it have the heating at idle before the adjustment?
Click to expand...
I’ve had the K5 for a long time and it was parked most of the summer months. It’s gone through a bunch of engine transitions from the original quadrajet GM stock TBI conversion to the top end with the MSD EFI. I rarely ran it in the summer. I knew I had an airflow issue and the AC sucked.

I tried e-fans and it stayed cool at idle but got warm / hot on the freeway on hot days.

It also did get hot under heavy load of the TBI. I just assumed it was running lean. That’s why I moved to the top end heads, cam and MSD. I should have gone to a 5.3, but didn’t.

It did get hot under the GM TBI setup as well, but I chalked it up to the stock heads and a poor fan shroud. I’ve addressed all that.
03CD992C-2748-45F1-99ED-361E7D0AA202.jpeg
 
Gasses don't look bad. You have room for a little richer.

So it seems like, you've hit all the common fixes.
So on to the unusual.

Flow through the rad. Question is to little or to much.
There are 2 inlet diameters for squares.
1 5/16" and 1 1/2". I had mine opened to 1 1/2".
To test the easiest would be to restrict the inlet, insert a sort tube the hose.
Add flow possibly take an old t stat and remove the valve.

My 2nd item is the trans cooler, is an automatic?
Heat from the trans may be overwhelming the internal cooler. Even if you also run an external cooler, which is not working at stops.
By pass the internal cooler to test this.
I bypassed mine and am happy. I did early fall last year, and haven't had the truck in the similar situation yet when I was having over heat issues.
I would recommend a large cooler with electric fan if you decide to by pass the rad cooler.
 
Wes Harden said:
Gasses don't look bad. You have room for a little richer.

So it seems like, you've hit all the common fixes.
So on to the unusual.

Flow through the rad. Question is to little or to much.
There are 2 inlet diameters for squares.
1 5/16" and 1 1/2". I had mine opened to 1 1/2".
To test the easiest would be to restrict the inlet, insert a sort tube the hose.
Add flow possibly take an old t stat and remove the valve.

My 2nd item is the trans cooler, is an automatic?
Heat from the trans may be overwhelming the internal cooler. Even if you also run an external cooler, which is not working at stops.
By pass the internal cooler to test this.
I bypassed mine and am happy. I did early fall last year, and haven't had the truck in the similar situation yet when I was having over heat issues.
I would recommend a large cooler with electric fan if you decide to by pass the rad cooler.
Click to expand...
I thought about those issues too. I took the transmission lines off from the radiator too to remove that influence. I put in the “Tru-Cool” LPD47391 cooler just behind the grill it’s place.

The lower radiator is 1.75 and the top is 1.5”. On the highway, no issues.

Maybe adding a little fuel at idle may help.

I’ve never let it get above 216 (from the MSD temp sending unit) so I don’t know what it would max out at. The temp reading is coming off from the temp sending unit on the intake. I’ve also checked it with an infrared and they are almost exact.
 
How much flow do you have in your radiator? Your trans cooler needs to be dumping a whole lot of heat in order to overwhelm you engine cooling system. I would be curious to know what your temps are at idle with the heater on full tilt boogie. Me personally, I would go with a 3 row aluminum radiator with the biggest flex fan you can find, but thats me. Then if you are borderline at that point, throw in an oil cooler with a temp controlled fan. That way if you are wheeling in summer when its nuclear hot, you wont torch your engine. Usually the line of troubleshooting goes, is the carb too rich, is the timing too far advanced, do you have adequate coolant flow, then do you have adequate air flow.
 
I don't know how much difference it makes, but that is the shorter of the two radiator heights. Roughly a 16% loss in size (purely by square inch) over the 19". I don't know what all GM saddled with the 17" radiator, but from my experience it was a lot less common to find than the 19".

If those are good/modern chamber heads (even moreso if AL) it should idle great at 20*, so unless fueling is lean I don't think you have a timing issue. But 14.7:1 is the norm for low load AFR, so doesn't sound like you are lean, either.

By any chance have you tried manifold+mech advance equaling 20* at idle, give or take a couple of degrees? Factory OBD1 stuff is all in the 20* range at idle/low load, just curious if you can get your setup in that range too.
 
When you went from V-belt to serpentine, you swapped to the reverse-rotation water pump, right? I don't know why, but sometimes water pumps are just bad these days. Also possible to get one mislabeled or in the wrong box, too.

How much is the fan turning at idle? Right after you shut it off hot, how hard is the fan to spin?
 
I had a problem with a 350 .030 over build on my ElCamino several years ago. Cooling at idle even with full fan shroud. Seems my issue was the high volume water pump. It was circulating the water before it had sufficient time to cool in the radiator. Once I went back to a normal pump flow 80% of the problem was gone. From there I just installed a set of Windstar electric fans w/thermal switch and was done.
 
Agree with @88Silverado, since the like button is fubar, gonna post pad now.

Put a restriction in the upper hose. Maybe reduce by 1/4".
Gotta be careful not to cavitate the pump.
 
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