Overheating at idle ... 1979 c10

[Cu1n81]

Hey guys,
I’ve got a 1979 c10 with a 350, 1406 edlebrock carburetor. Truck has been running fine. Had the radiator flushed, water pump is good, coolant is full, new thermostat placed in it last week, and I just installed 2 new electric fans. Both are blowing towards the engine.

The truck runs great and stays cool if I’m out on the road. Once I sit in the same spot or go thru a drive thru, the temps slowly rise until the truck will no longer idle without help from me giving it gas and it will eventually overheat.

If I arrive at the drive thru at 150 degrees, within 10 mins it will overheat and start lowering rpms at idle until it starts to choke off. Overheats around 215+.

What is the issue? The fans together push about 1600 cfm’s. I have read v8’s need a minimum of 2600 cfm’s. Could that be the issue when I’m idling?

Cools great will cool clean air blowing thru the radiator. Just when it idles very long. The local shop says it’s fine. Shouldn’t these trucks be able to idle as long as needed? I don’t have an AC that is working currently.

 

[Charlie]

A pic of your setup would help to see what you have. In my opinion, I would not think 1600 cfm from 2 fans would be enough. If they were 1600 cfm each, I would think that would be sufficient.

 

[Bextreme04]

Hey guys,
I’ve got a 1979 c10 with a 350, 1406 edlebrock carburetor. Truck has been running fine. Had the radiator flushed, water pump is good, coolant is full, new thermostat placed in it last week, and I just installed 2 new electric fans. Both are blowing towards the engine.

The truck runs great and stays cool if I’m out on the road. Once I sit in the same spot or go thru a drive thru, the temps slowly rise until the truck will no longer idle without help from me giving it gas and it will eventually overheat.

If I arrive at the drive thru at 150 degrees, within 10 mins it will overheat and start lowering rpms at idle until it starts to choke off. Overheats around 215+.

What is the issue? The fans together push about 1600 cfm’s. I have read v8’s need a minimum of 2600 cfm’s. Could that be the issue when I’m idling?

Cools great will cool clean air blowing thru the radiator. Just when it idles very long. The local shop says it’s fine. Shouldn’t these trucks be able to idle as long as needed? I don’t have an AC that is working currently.

We definitely need pics of this setup. 1600 CFM is Honda civic electric fan territory. The stock GM truck dual electric fans are in the 3-5000cfm range total. Also, if you don't have a fan shroud for those dual fans you are going to have a big problem with it only pulling air through a small portion of the radiator as well.

 

[dvdswan]

Are the fans always on or are they on temp control? And I agree with the fan shroud ^^^

 

[75gmck25]

If you really want to use electric fans, the Ford Taurus (87-93?) dual speed and the Ford Windstar (99-03?) dual fans are a common solution. Pull the fans, shroud and the controller and relays from the junkyard. They pull a lot of amps and the stock controller relays can handle it better than cheap aftermarket relays. The fan assembly with shroud is also sold by Dorman at most parts places, and a new one is probably about $110-150.

 

[burkeftm]

Are you running stock exhaust ? If so check to see if the heat riser os stuck closed on the right exhaust manifold . I had the same issue with a 78 c20 would overheat at traffic lights cruising down the road it would go back to 180 . Everything on my truck was stock , i also went thru changing waterpump , thermostat ect and it was almost fully closed heat riser .

 

[Jimmy84]

1 of the benefits of the vacuum advance is allowing the engine to run cooler at low rpms.
That said, if the fans are too low in flow or un-shrouded, that's a big problem. Heat riser function is also a good recommendation.

 

[Jimmy84]

1 of the benefits of the vacuum advance is allowing the engine to run cooler at low rpms.
That said, if the fans are too low in flow or un-shrouded, that's a big problem. Heat riser function is also a good recommendation.

 

[Ken Boellner]

Flushing a radiator does nothing. It has to be rodded out and most places don't do that.

 

[Raider L]

@Cu1n81,

Do you have a stock fan on the engine, not those flimsy stainless bladed things people used to run, but the good 'ol steel 6, 7 bladed fans? I don't get why it won't cool while at a stop in traffic or waiting in a line. The engine isn't running at a high rpm generating more heat unless you don't have enough shroud or the fan is in the wrong place in the shroud, maybe? To far in, or to far out? And like @Ken Boellner indicates the radiator could be stopped up somewhere in it's core and the only reason why it cools at speed is because the water pushes through, and more of it into the radiator, and obviously the wind going through the radiator cools the water.

I think I would check to see if the radiator is clear first, since you said you did everything else already.

 

[Raider L]

@Cu1n81,

Man, if I saw my temp go to 215 I would freak out!! The only time I've seen temps over 200 was one time I was in a group of hot rods going to Longview, Texas to a car show on a very hot summer afternoon on interstate and the lead car was doing over 80 mph. Running, my temp showed 205 and I was freaking then. I almost pulled back and slowed down. I would have thought a head would crack at 215! Or a blown head gasket or something else equally as bad.

 

[Cu1n81]

Here is my current setup:

Thanks for the replies so far. I will definitely check these items. Currently these fans run all the time. I haven’t put the fan thermostats on yet. Once I realized I had too little air flow from these fans, I figured it wouldn’t hurt it to run all the time.

I’m looking for a shroud now. If anyone has a link to one they suggest I’d be appreciative.

And to be clear the truck handles 99% of driving fine. I drove thru traffic just fine the other day. It was stop and go. But I had runs where the air could get thru it and kept it cool. I definitely can’t let this truck idle for an hour or something like that. It would over heat.

The truck isn’t stock. It has a mild cam. A few other mods. I just bought it about 2 months ago.

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[Dave M]

Simple solution, you need a shroud. Have a look at the size of the surface area of the actual radiator core, at idle you are only pulling air through the core, the diameter/size of the fans. (shaking my head in disbelief)

 

[RecklessWOT]

^ This.

At idle you are only pulling air through the two little areas covered by the fans. Once you get moving there is plenty of air passing through that big aluminum radiator (which is nice btw) so it cools well. Plain and simple without a shroud you are not moving air across enough of the surface area of the radiator. I would almost guarantee that's your problem especially since it cools just fine until you start relying on the fans to do all the work, fans only do anything when sitting still. For a short while I had a truck with no fan whatsoever and it ran/cooled just fine as long as I kept moving but If I hit a red light I had to shut it off. You might get away with it if you had some huge fans on there that covered almost the whole radiator, but those look like the little ones you can buy off the shelf at advance auto. Not only do they look a little too small but without a shroud the air is not being directed across a large enough area of the radiator, that big ole iron v8 makes a lot of heat

 

[Raider L]

@RecklessWOT,

That is exactly what I was thinking was the fans look a bit small. I hope you, @Cu1n81, kept your receits, always keep your receits for anything on your truck. I('m pretty sure you can get fan s that come with a shroud built on the pair of the fans. It clips to the radiator around the edges somewhat. That would be better than nothing like you have it now. In getting the larger fans you get the shroud along with them.