What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

2000 GMC Yukon 5.3L overheating - fixed with thermostat/pump replacement

ekajkrats

ekajkrats

1/2 ton status
Joined
Mar 6, 2012
Posts
1,666
Reaction score
1,423
Location
North SF Bay Area, CA
Hey all, I need your help

So my wife was driving the Yukon on the highway this morning and she pulled over when she saw a low coolant light and the temp at 260. As she was searching for a place to pull off the highway I had her turn the heat on and she pulled off and shut off the suv. She wasn't too far away so I got in our other car and drove to her so she could take the kids and finish her errands.

When I checked the coolant reservoir it didn't look low. But best I could tell was that coolant was being pushed out of the reservoir. So I added a bit more dexcool to make sure it had enough. As I added it while it was running, it pushed more out the overflow tube. At that time I also had put my odb2 scanner on and the app showed me at 210. It idled there at 210 just fine. So I decided to go for the next exit keeping an eye on it.

It started to creep up to 220 and so when I was off the highway (1/2 mile) I pulled over and then it started to drop to 215 as I idled. I drove down that road to another parking lot and again it began the creep up to 217 so I decided to have a tow back to my house.

Here are the quick details:
5.3L with 135k miles
Low coolant light came on for her, didn't return for me
Temperature keeps going up on highway and roads
Not seeing white smoke out tail pipe
Not seeing any other coolant leaks except out overflow tube on reservoir
Temp gauge in dash is no good (showed her 260 but when I started it up and drove, never moved from 210 while app showed changes)
Not seeing any white residue or coolant leaks at thermostat or anywhere else on hoses or water pump

What are my best next steps to diagnosing it? Thinking of doing the thermostat and water pump as well as hoses, as I have not done it in owning it since 85k.

Thanks!
Jacob
 
low coolant ? if so the vortec engines are noted for bad gaskets for pump to block for h20 pump mounting .

also run with a scanner to verify coolant temp date as the dash clusters are known for problems on 99-up and can show funky readings before they stop working .
 
What year is it? Have you ever done the intake manifold gaskets? Dexcool can get funky when air is entering the system and start gumming things up. Could be a bad radiator cap, or even just the o-ring on the cap.

EDIT: oops, didn't read the title. A 2000 would have the failing intake gaskets, so plan to do that if the upgraded version hasn't already been installed.
 
Blue85 said:
What year is it? Have you ever done the intake manifold gaskets? Dexcool can get funky when air is entering the system and start gumming things up. Could be a bad radiator cap, or even just the o-ring on the cap.

EDIT: oops, didn't read the title. A 2000 would have the failing intake gaskets, so plan to do that if the upgraded version hasn't already been installed.
Click to expand...
I haven't done the manifold gaskets before, and not sure on the P.O. Thanks for the direction. If this were the case would I see air coming out through the reservoir regularly? Any other symptoms before I tear into it?

I did order a new reservoir cap.
 
As I think about this, I remember that the truck LS has a dry intake. When the gaskets go, unmetered air enters the engine and it runs bad, idle gets unstable, etc., but it really has nothing to do with coolant. There are several places that like to develop leaks, like the water pump gaskets and the plastic heater hose fittings, but you should see coolant coming out if any of them are bad.
 
If it was low on coolant and there’s no leak, I’d pull the plugs and see if one looks like it’s been through a parts washer. Also look at the oil, if it’s a milkshake you know it’s a cracked head/bad HG.
 
skunked said:
If it was low on coolant and there’s no leak, I’d pull the plugs and see if one looks like it’s been through a parts washer. Also look at the oil, if it’s a milkshake you know it’s a cracked head/bad HG.
Click to expand...

It's definitely not milkshake, very clean. Need to pull the plugs. I wonder if the Low Coolant came on because it was boiling the coolant and pushing it out the reservoir? Not sure where that sensor is.

Kay86K5 said:
thermostat
Click to expand...
Going to swap that out today. Would be nice if that does it!

Thanks guys!
 
ekajkrats said:
It's definitely not milkshake, very clean. Need to pull the plugs. I wonder if the Low Coolant came on because it was boiling the coolant and pushing it out the reservoir? Not sure where that sensor is.


Going to swap that out today. Would be nice if that does it!

Thanks guys!
Click to expand...
I had a similar problem on my 97 it was a plugged radiator
 
ekajkrats said:
Working my way to that. Got home too late to work on it in the driveway tonight. I'll have to make some time for it tomorrow.
Click to expand...
For me the way I found out is that it was building up too much pressure and when I removed the thermostat to see if it was the problem, the hose blew off the radiator telling me no,it's not the thermostat. I ended up cleaning the radiator in a crazy way and it worked, but now a few months later the water pump is leaking. :doah:
 
I have an 02 with 285k and I’ve never touched the radiator, it’s still original. The pump started leaking at 230k so that’s been replaced along with the thermostat and the hoses. Another common cooling system leak on these trucks is the plastic firewall fitting for the heater core. I kept needing to add coolant every few months and we never had coolant puddles on the ground. Eventually I figured out the firewall fitting would drip (very slowly) onto the valve cover and header. This was not causing an overheat issue however it could explain your low coolant light.
 
So I replaced the water pump and thermostat (as well as the belts and upper and lower radiator hoses) and that did the trick. I didn't inspect the old pump other than to make sure it was the same as what I was installing, but my money is on the thermostat.

The temp just goes between 186 and 190 now which means the radiator is working properly. After assembly I did have a leak at the lower hose connection to the pump, but after re-positioning the clamp, it seems to be good to go now.

Before I installed those parts I did flush the radiator to try and get any buildup out but nothing came out.

I'm just glad that was all it was. And I got to use my Christmas present, the Milwaukee ratchet:
IMG_20200109_163458.jpg

Thanks for all the help guys!
 
ekajkrats said:
So I replaced the water pump and thermostat (as well as the belts and upper and lower radiator hoses) and that did the trick. I didn't inspect the old pump other than to make sure it was the same as what I was installing, but my money is on the thermostat.

The temp just goes between 186 and 190 now which means the radiator is working properly. After assembly I did have a leak at the lower hose connection to the pump, but after re-positioning the clamp, it seems to be good to go now.

Before I installed those parts I did flush the radiator to try and get any buildup out but nothing came out.

I'm just glad that was all it was. And I got to use my Christmas present, the Milwaukee ratchet:
View attachment 324888

Thanks for all the help guys!
Click to expand...
:waytogo:
 
You must log in or register to reply here.

Latest Posts

Top Bottom