Odd overheating issue

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Originally Posted By: eljefino
Originally Posted By: mechtech2

Also, a bad WP impeller [corroded or loose] can cause tough to determine problems.


This. Next time it happens, crank the heat. If the water pump is working right it should be scalding hot. If it's tepid, you have water flow issues.


A very good point. This isn't nearly as common as some of the other things and is often overlooked until everything else has been tried (or tried twice...)
 
Definatly an air flow problem. Since GM has gone to dual electric fans on this truck and they are working the next step is to remove the plastic core support cover and make sure that theres not tons of dirt, fuzz or even a trash bag stuck between the condensor and Radiator.

BTW: These trucks are the ones that are constantly being towed in to my shop due to overheating when heavily loaded and pulling Cajon pass.
 
I would check the fan first, make sure the radiator is clean on the outside and the thermostat is working properly. When was the last time the cooling system was flushed? Slow flowing coolant through the radiator can cause the problem you are describing along with a sluggish thermostat.
 
OMG. A few of us haven't kept up with technology!

All electric variable speed fans are standard on that truck. if they're on they are likely not the issue.

The water pump impellers are also not a factor on this truck. The water pump lasts almost forever with no fan mounted on it!

My bet is the thermostat. Good luck to the OP.
 
Originally Posted By: OVERK1LL
Originally Posted By: TomYoung
Originally Posted By: OVERK1LL
Sounds like a failure of the fan clutch.
Maybe in 1975 it sounds like that. I would be shocked if this vehicle has an engine-driven fan.

This problem is simple -- for some reason the electric rad fans are not turning on when the engine is idling. Check more or less in this order, fuses, relays, solenoids, fan thermostat/switch and finally that the fans will run when receiving current.


My M5 has an engine driven fan and so does my Expedition. Neither are from 1975 sir. You'd be surprised at the number of vehicles that have retained this setup through the last decade.

Quick Google:

miyb3121_d.jpg


2009-2010 Ford F-150 Fan Clutch - Motorcraft - Standard thermal

The OP later clarified that it was electric, however I don't think there is anything wrong with me assuming it MIGHT be mechanical.


Sorry folks -- got this one way wrong!
 
Originally Posted By: SteveSRT8
OMG. A few of us haven't kept up with technology!

All electric variable speed fans are standard on that truck. if they're on they are likely not the issue.

The water pump impellers are also not a factor on this truck. The water pump lasts almost forever with no fan mounted on it!

My bet is the thermostat. Good luck to the OP.


Well, I actually have a continuously-variable speed electric fan on my '66 (aftermarket controller, large Ford fan) so I know the tech... but I didn't know that particular tech was standard on mid 2000s GM trucks. ;-)

I still can't fathom how a thermostat problem would overheat it *sitting still*. Restricted water flow usually creates overheating at high speed and under load (unless its a water pump problem), weak air flow usually creates problems sitting still. I know of exceptions (my '69 will overheat on the highway if the fan isn't working because of the aerodynamics... or lack therof... not moving enough air through the grille at speed), so I suppose its possible.
 
Originally Posted By: 440Magnum
Originally Posted By: SteveSRT8
OMG. A few of us haven't kept up with technology!

All electric variable speed fans are standard on that truck. if they're on they are likely not the issue.

The water pump impellers are also not a factor on this truck. The water pump lasts almost forever with no fan mounted on it!

My bet is the thermostat. Good luck to the OP.


Well, I actually have a continuously-variable speed electric fan on my '66 (aftermarket controller, large Ford fan) so I know the tech... but I didn't know that particular tech was standard on mid 2000s GM trucks. ;-)

I still can't fathom how a thermostat problem would overheat it *sitting still*. Restricted water flow usually creates overheating at high speed and under load (unless its a water pump problem), weak air flow usually creates problems sitting still. I know of exceptions (my '69 will overheat on the highway if the fan isn't working because of the aerodynamics... or lack therof... not moving enough air through the grille at speed), so I suppose its possible.



Mark VIII fan by chance? I retrofit one to my Town Car. They move an obscene amount of air.
 
I have had sticky thermostats that benefited from having a small hole drilled in their flanges, to help burp air and or help water flow "tickle" the pellet and get it to work. However, they usually stick closed for the warm up cycle then fly open when the engine is revved, then keep working the rest of the drive cycle.

It may be time to start squeezing various hoses to test for warmth and the sensation of water flowing. Rad hoses and heater core ones.
 
Need more info:
Anything done to the vehicle lately? Did you check the fluid level? Does it have the original fluid in it?
 
Originally Posted By: Chris142
If it was a thermostat problem it would run even hotter going down the road. But it doesn't. It cools down.

I'm still betting on plugged Radiator fins.


Listen to Chris; he runs a radiator shop. I recently dealt with this exact scenario, and when I got a view of the front of the radiator, it was plugged with dirt, dust, bugs, and fuzz.
 
That's funny, it's usually the simplest thing!

Yeah, you should check the fluid level because the overflow tank is a poor indicator if your cap is messed up or there's a leak somewhere.

Where are you guys driving with all these bugs? I live in Florida and it's bug city down here. We have trucks with gazillions of miles and the radiators do not get plugged up at all.

And Overkill/440, my old hot rod truck has a Flexalite fan system on it that has a variable speed controller and flows 6000 cfm on max! Draws so many amps it'll almost stall the truck if it gets excited.
 
Steve, I'm as puzzled as you are about the bugs. I've lived in Florida my entire life and I've never had a radiator plug up or even noticeable bugs on it even during love bug season. I know it can happen, but just never have seen it. Maybe all the rain we get washes it out.
 
Some cars definitely suck up bugs more readily than others although I would think the condenser would clog up first and you'd notice the poorly operating A/C before it ever affected the radiator.
 
Same here as bigmike..I generally go out to Tampa twice a year in the spring and the the love bugs are a nightmare..I generally have to stop at least 8 times each way to clean off the windsheild..This year was the worst on I-75 and I-275..Never had a radiator plug up because of that..I guess the monsoon rain keeps everything under control.
 
Originally Posted By: SteveSRT8
That's funny, it's usually the simplest thing!

Yeah, you should check the fluid level because the overflow tank is a poor indicator if your cap is messed up or there's a leak somewhere.

Where are you guys driving with all these bugs? I live in Florida and it's bug city down here. We have trucks with gazillions of miles and the radiators do not get plugged up at all.

And Overkill/440, my old hot rod truck has a Flexalite fan system on it that has a variable speed controller and flows 6000 cfm on max! Draws so many amps it'll almost stall the truck if it gets excited.


Now imagine close to that kind of airflow from ONE fan
wink.gif
The Mark VIII fan is NUTS. Even with a DCC controller, you can tell when it starts ramping up on my buddy's '91 notch.

There's something to be said about a good quality electric setup. I have no experience with them on trucks however. Just cars.
 
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