01 Denali Overheat

[aaford72]

My 2001 Denali has an overheat issue when the AC gets turned on. Will rise from 210 to about 245.

Turn AC off and will slowly start to cool back down. Already did a coolant flush and new thermostat in the past 10 days and still having the issue. Took it to a garage they initially thought it was intake gasket. Opened up and found that it is not the case. Now they believe it is head gasket. They called and said that they see a small coolant leak coming from back of block when under pressure (18 pounds for over an hour). They want to replace head gasket and have head and other components machined (cost over $2500).

Does this all seem correct or are they trying to take me to the cleaners?

Can I just drive without AC or do you think that there is another issue with AC causing the issue?

Thanks!

 

[about20ninj45]

If your mechanical inclined you can do the head gaskets yourself for about 300 or so. I'd check to see if your fans are turning off when your running the AC. Do you have a clutch driven fan or electric fans?

 

[Danny3737]

The first thing I would check is the fan clutch. They are known to go bad.

 

[about20ninj45]

If your mechanical inclined you can do the head gaskets yourself for about 300 or so. I'd check to see if your fans are turning off when your running the AC. Do you have a clutch driven fan or electric fans? You wouldn't need the heads machined unless you warped them, which is rare in most cases.

 

[#1taho]

What style fan do you have ? Electric or clutch fan ?

I would think it's a fan problem!!
These trucks don't really get blowed head gaskets. So I would be surprised. But you could have another coolent leak. Coolent hose at the back. Or byroads hose. Maybe even a frost plug. But start with the fans. That's were I and most of us would start

 

[afpj]

If that garage suspected the intake gasket as part of a cooling system issue, I would go to another garage. These vehicles have dry intakes, meaning no coolant goes through them. They do not know what they are doing, Runaway.

 

[aaford72]

I went to the garage and looked at it myself. There is a very slight leak coming from the backside of the motor. At this time I have asked them to put it back together and I will look for a second opinion. They claim that the small leak causes air bubbles and is why it will start causing the temp to go up. I have never heard of this myself.

It is a clutch driven system. They claim to have tested the fan clutch and it is strong. Not sure what to check next.

 

[bottomline2000]

How old is your water pump

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[afpj]

The air bubble thing is real, so they're not FOS there. As far as coolant on the back side of the engine, the only place I can think of off the top of my head is the coolant to the heater hoses spraying down. That would be a fairly common issue depending on the age and maintenance of your vehicle. However head gasket leak is also a possibility but that'd be pretty rare as others have said. Good luck

 

[aaford72]

How old is your water pump

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Not sure. I have only owned the yukon for 3 months. They did say it looked good.

 

[6speedblazer]

i would start with the basics on a truck this old.

First things first. hose out the AC condenser and radiator. most people are surprised how much shit can come out of them.

Next check the fan clutch

finally check the AC, the evap could be icing up making the condenser overheat. that will strain any cooling system to the max. or air in the system makes the compressor strain and pump out more heat.

as far as coolant leaks at the back of the motor, i have seen more steam port block off plugs leak than i have bad head gaskets.

 

[Chubbs]

I just sold a Land Rover to get into the Yukon and head gasket leaks are a real thing that will cause your engine to overheat. Never overheat your engine or let it run low on oil, if you don't like major expenses like an engine rebuild, for instance. I had to rebuild the whole top end on the Land Rover because the head gaskets were leaking and it was a real, true PIA. I did the repair myself for under $1,000 and took me about 3-weeks but that involves doing everything properly the 1st time. It can be done faster & cheaper, especially if you know what you are doing but you run the risk of having a faulty rebuild or problems elsewhere like valve-train or vacuum leaks if you throw it together quickly & miss something or have a bad seal somewhere at the intake manifold or the like. It costs a small fortune in labor charges to hire a qualified garage to make the repairs. Also, a rule of thumb is to remanufacture the cylinder heads themselves prior to reinstalling on the fresh gaskets. Rule number 2 is do both banks, not just the 1 head which is leaking. So anyways, $2500 has always been the going rate for a V8 head gasket repair. If you shop around you should be able to find a cheaper rate but you know what they say about cheaper. Finally, you can buy a radiator pressure tester @ Harbor Frt for $60-70 last I checked. Simple to use and allows you to find what is actually leaking the coolant & where. You said the garage showed you the leak, was it under pressure at the time and was the origin of the leak pointed out to you? Anybody can find the coolant trail and put your finger on it but unless you saw that coolant leaking from exactly the interface of a cylinder head & engine block then have the next garage you go to put the coolant system under pressure and call you over to show you this leaking head gasket: they always will if it's a $1000+ repair. Don't drive the truck anymore until the coolant leak is fixed or else you will be rebuilding your engine or purchasing another 1 altogether. I have never heard of a faulty HG pronouncing itself only when the AC comp is activated but whatever; it's only going to get worse to the point where the gasket leaks under all conditions and pukes all of the coolant, frying your engine and warping the cyl-head/eng block interface making it a junk sandwich.

 

[rockola1971]

Its very easy to blow a head gasket on the LSx engines. Just get a thermostat stuck closed and drive it and you will find out. Or get any kind of leak and let it get in the red and continue driving it like that and you will find out there too.

WTF? A garage says "theres coolant coming from the back of the engine". Ok. Well are we playing a guessing game here? Do they not know where it is coming from? Do their eyeballs work?

 

[RED TAHOE LS]

Now they believe it is head gasket.


Time for a new garage.
David g............

 

[VikingTrad3r]

i dont see the connection between the ac and the headgasket.

compressor turns on and then uses up some of the cool air and starves the rad for cool air?



can you verify that your denali overheats without ac on?

IF IT is your head gasket you would be seeing temps climb up while stuck in traffic on a super hot day even without ac on.



i cant believe im saying this, but due to the nature of the leak on the back of the block i would actually try a few of those gm oem cooling system "pills". they are designed to stop small leaks without killing the entire system.

no f'ing way would i let that shop touch my truck after they told you coolant leak was from the intake gasket. they are clearly used to sbc not lsx. did they charge you shop time for this????

they shouldnt because its impossible that this was the cause due to the nature of the lsx.

 

[rockola1971]

When AC is on it loads engine down some. Causes engine to run hotter.

 

[bottomline2000]

When the ac is on the condenser heats up and if there is air in the system the condenser can get hotter that normal making the cooling system less efficient.

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[VikingTrad3r]

yah but barely!

im skeptical of a head gasket.

 

[rockola1971]

yah but barely!

im skeptical of a head gasket.

A simple compression test should show a leaking head gasket. Could be a cracked head too.

 

[VikingTrad3r]

true. in fact OP you should get the shop to do a leakdown test. that will tell you with 100% certainty if its a cracked head or head gasket.


also, something i had recently was a crack on the driver side of the radiator. inswapped it out for a spectra.