08 Silverado Overheating

02slt · August 2, 2011

my 08 Silverado ( 5.3 ) overheats on the highway when the AC is on, after about 20 minutes of driving on a hot day. The engine overheating ( temp gauge 3/4 of the way or higher ) in turn drives the tranny temp up (4l60) to about 110 degrees celcius.

My truck has 130,000 km on it, and has been dealership maintained.

My last visit to the dealership, they said there was a thermostat code coming up, so they replaced the thermostat and flushed the coolant ($300ish) But my truck still overheats.

I was a little disappointed to find out that the $2800 extended warranty I purchased from the GM dealership I bought my truck from, did not cover a thermostat.

I'm not sure if this is related, but my volt gauge usually drops to 1/4 shortly before the engine & tranny temps go up. Once I get off the highway, the volt gauge goes back to 1/2, and the engine and tranny temps go back to normal.

Any ideas?

chrisjr123 · August 2, 2011

I believe you have a flow restriction possibly a failed thermostat out of box or massive air pocket

02slt · August 2, 2011

Thermostat was just replaced, unless for some reason the new thermostat was also faulty

AirForceAngler · August 2, 2011

If the last work done on the truck was a new t-stat and now it's overheating, I'd start there.

wavery · August 2, 2011

Normally, I would say that the first thing you should check is the last thing that you replaced. Defective new parts or faulty installation do happen. However, if you were over-heating before the new thermostat, that's probably not the case.

You may have a bad w/pump.

If it were me....... I'd pull the radiator, take it to a radiator shop to get cleaned and replace the w/pump........... but that's just me, I do my own work.

TexasAl · August 2, 2011

Make sure your electric fans are turning on. I believe both fans need to be on when the A/C is on. To check, simply turn on the truck with the A/C on, and verify that both fans are working. If they are working, then I'd replace the thermostat again (it is cheap ), and check the radiator cap and radiator. Finally, I would get the water pump removed, and make sure it is working properly.

Sierra6.0 · August 2, 2011

How many miles are on your rig? I know it is an '08, but if you are around the 80k~100k mark, just do the entire cooling system:

Radiator, water pump, hoses, t-stat, overflow tank, flush fluid, etc. The reason why, is that once a cooling system part fails, the rest are on borrowed time. For most vehicles this is around the 100~130k mark, but some newer high-performance and modern applications that use a lot of plastic for cost and/or weight savings can fail around 80k.

I used to replace cooling system parts as they failed on my '94 firebird and '94 grand cherokee. All I was doing was chasing parts and draining fluids until I eventually replaced everything (destroying an opti-spark in the process). Before I traded my 540i, I had an upper radiator hose burst at 80k, plastic failure. This time, I bought me a temporary hose to get me through the rest of the summer and winter and the following spring did the entire overhaul during a weekend on my own time. Good to go for another 80k~100k with no worries. With any car now, I plan to do the overhaul once once component fails. Most modern cars use a ton of plastic not to mention the rubber which fails over time with hot/cold cycles. It's much cheaper in the long run, as draining your system isn't cheap, nor fun.

Back to your original overheating problem. If you have 80k, just do everything. Chances are you'll take care of your problem with the overhaul, and add some reliability to the system all in one fluid change. Now you are on fluid change #2. Do you want to drain your radiator a 3rd time?

That said, if you have under 80k, I'd just replace the T-stat like others have mentioned. You might have just one faulty component and everything else has life left. If you have 80k+, I would do a new T-stat, water pump, and hoses minimum. Get it over with.

Just my two cents.

EDIT: Just noticed you said 130km. Sorry, not paying much attention today. That's 81k miles. Just do the overhaul. It is time. Probably early on a truck engine, which are usually build heavier, but do you really want to do it a year from now when something else dies and you are closer to 100k?

02slt · August 2, 2011

thanks for the input

I already had the overheating problem before I took the truck in for service, GM replaced the thermostat, but the truck still overheats.

I'm hoping any subsequent repairs are covered under the bloody expensive (but so far useless) extended warranty I bought

tanked_darren · August 2, 2011

funny they threw parts at it but never fixed the problem while still charging you! You got suckered in!

wavery · August 2, 2011

Make sure your electric fans are turning on. I believe both fans need to be on when the A/C is on. To check, simply turn on the truck with the A/C on, and verify that both fans are working. If they are working, then I'd replace the thermostat again (it is cheap ), and check the radiator cap and radiator. Finally, I would get the water pump removed, and make sure it is working properly.

Fans was my 1st thought, then I noticed the OP stated, "overheats on the highway when the AC is on, after about 20 minutes of driving on a hot day."

If the fans weren't working, the engine would over-heat in slow driving. It should cool down at higher speed highway driving. That indicates a lack of coolant circulation.

Check your warranty to see if it covers the w/pump. Some do, some don't. Like you say, most of those policies are worthless and the dealers hate them.

If it covers the w/pump, just pay them extra to pull the radiator and send it out for cleaning. The tech will love you because pulling the w/pump is a piece of cake with the radiator out....... although, he will flat-rate it anyway......

If you don't plan on keeping the truck for more than 2-years, leave the radiator and just have them do the w/pump if it is faulty.

They should have done a "Block-check" too, to rule out a bad head gasket.

02slt · August 2, 2011

All the fans work, my truck sounds like a 747 once I get off the highway.

Looks like water pump IS covered, so hopefully that's the issue.

How many hours do you think it would take to pull the rad and send it for cleaning?

I'm currently laid off, so I need to watch my spending

Debo511 · August 2, 2011

Water pump impeller spinning on the shaft at higher speeds........ No need to replace the whole system, hoses yes. Never had the need to pull the radiator and have it "cleaned" except on S-10's with 4.3 and dexcool.

02slt · August 2, 2011

Dealership called, they can't find anything wrong with it

despite the engine gauge showing 3/4 full

Guess I'll try another dealership

wavery · August 2, 2011

All the fans work, my truck sounds like a 747 once I get off the highway.

Looks like water pump IS covered, so hopefully that's the issue.

How many hours do you think it would take to pull the rad and send it for cleaning?

I'm currently laid off, so I need to watch my spending

I'm not sure that you would want to take that on yourself. Not that it's a huge job, just that the A/C condenser has to be removed too. That means protecting the system, evacuating and recharging the A/C after everything is back together.

That's sorta why I made the comments, "If it were me....... I'd pull the radiator, take it to a radiator shop to get cleaned and replace the w/pump........... but that's just me, I do my own work." and...... "If you don't plan on keeping the truck for more than 2-years, leave the radiator".

This wouldn't be a cheap or easy job by any stretch. It just depends on how long you're going to keep it and how much $ you are willing to spend to resolve the issue and feel confident that the radiator isn't the problem.

Let me ask you something....... Have you ever had a coolant leak in that truck and put any kind of stop leak in it?

The simpler thing to do would be to take the truck to your local radiator shop. I'll bet they would conduct a flow test pretty cheaply.

One other thought........ do you have a trans cooler on your truck?