New thermostat Friday, coolant leak today

[HawkeyeScott]

1997 GMC Yukon 5.7L with 167k miles I bought a few months ago as a cheap third rig. I've slowly been crossing stuff off the to-do list to get it baselined.

I installed a new thermostat over the weekend. In the process, I lost about 40 oz. of coolant, which I replaced with distilled water. This morning, I noticed a puddle of coolant under the vehicle at one of the stops I made on the way into work. I stopped and bought a cheap plastic pan to slide underneath so as not to make a mess at work. I checked the pan about two hours later and saw just a few drips, which leads me to think it's only leaking when the truck is running.

Did the new thermostat increase the pressure in the system and I just exposed a weak spot ? I haven't tossed the old one yet - I'm half tempted to re-install and see if the system leaks.

If I do have a leaky radiator, is there a preferred stop-leak that would work in this system? FWIW, the previous owner has green coolant in it.

 

[Alfred_B]

Maybe you had the coolant pool somewhere when you lost the 40 oz and that's what the puddle was.

 

[HawkeyeScott]

I wish that were it, but I'm afraid this was an active leak this morning.

 

[Rand]

something you disturbed is now leaking. Sometimes taking apart a system that is 20 years old the hoses etc will no longer seal when you put it back together.

 

[Wylie6G72]

Old hoses don't like to be moved around. I ended up replacing all the odd coolant transfer hoses when I replaced the thermostat in my '82 Mustang, because moving them caused pin holes to develop. If you're sure the housing gasket isn't leaking, a hose is your culprit.

 

[exranger06]

Get a cooling system pressure tester and do a pressure test. It's possible and very likely it's only leaking when the truck is running, or at least it leaks worse when it's running vs shut off/cold, since the system builds pressure as the engine heats up. You'll probably find the leak almost immediately when you do the pressure test. I always do a pressure test anytime I've opened up the cooling system. That way I can be sure I put everything back together correctly, and that there are no other leaks in the system. I can't tell you how many times I've found unrelated leaks elsewhere in the system that I would've never even known about otherwise.

 

[Chris142]

Originally Posted by HawkeyeScott


If I do have a leaky radiator, is there a preferred stop-leak that would work in this system? FWIW, the previous owner has green coolant in it.

No stop leak will work on plASTIC RADIATOR TANKS IF THATS WHATS LEAKING.

 

[nascarnation]

Originally Posted by Chris142
Originally Posted by HawkeyeScott


If I do have a leaky radiator, is there a preferred stop-leak that would work in this system? FWIW, the previous owner has green coolant in it.

No stop leak will work on plASTIC RADIATOR TANKS IF THATS WHATS LEAKING.


If you plan on keeping this rig, new radiators are pretty cheap. You can get a Denso from Rockauto for a bit over 100 bucks. Stop leaks are always a chancy proposition often not working or plugging passages you don't want plugged.

 

[Supersonic]

On 2005 Camry rubber seal/gasket at the thermostat housing wasn't thick enough for a good seal, bought an Aisin brand seal and it was just a little thicker and cured the leak.

 

[perfect_oil]

Don't rely on that thermostat seal by itself, use a housing gasket along with it, or use RTV on the flange part of the thermostat housing if a gasket isn't available. I know they come from the factory without a flange gasket, but mine leaked without a flange gasket installed after replacing the thermostat and its included seal.

 

[The_Nuke]

Originally Posted by HawkeyeScott
1997 GMC Yukon 5.7L with 167k miles I bought a few months ago as a cheap third rig. I've slowly been crossing stuff off the to-do list to get it baselined.

I installed a new thermostat over the weekend. In the process, I lost about 40 oz. of coolant, which I replaced with distilled water. This morning, I noticed a puddle of coolant under the vehicle at one of the stops I made on the way into work. I stopped and bought a cheap plastic pan to slide underneath so as not to make a mess at work. I checked the pan about two hours later and saw just a few drips, which leads me to think it's only leaking when the truck is running.

Did the new thermostat increase the pressure in the system and I just exposed a weak spot ? I haven't tossed the old one yet - I'm half tempted to re-install and see if the system leaks.

If I do have a leaky radiator, is there a preferred stop-leak that would work in this system? FWIW, the previous owner has green coolant in it.


Find the source of the leak first and go from there.

 

[HawkeyeScott]

Update: It appears the idiot mechanic failed to properly tighten the hose clamp. Of course, I am that idiot.

My neighbor came over to talk about his upcoming hunting trip as I was finishing up. Apparently I was a little too into that conversation.

A great reminder to pay attention when doing a job and then check the easy stuff first when there's a problem.

Thanks everyone.

 

[andyd]

EHHH I resemble that !

 

[clinebarger]

Originally Posted by exranger06
Get a cooling system pressure tester and do a pressure test.


I never recommend pressure testing a 4.3L/5.0L/5.7L Vortec unless you're sure it's had the intake gaskets replaced recently OR has metal carrier gaskets!

Let the engine warm up to operating temp & naturally build pressure, If it won't build any pressure.....You can now pressurize it with a hand pump while the engine is still warm.

I had a few techs over the years get aggressive with the hand pump on a cold engine & blow a gasket out, Then come to me saying it needs Intake Gaskets when in fact the Water Pump is what was actively leaking. Now the shop & tech has to eat the water pump & labor.

 

[clinebarger]

Originally Posted by perfect_oil
Don't rely on that thermostat seal by itself, use a housing gasket along with it, or use RTV on the flange part of the thermostat housing if a gasket isn't available. I know they come from the factory without a flange gasket, but mine leaked without a flange gasket installed after replacing the thermostat and its included seal.


I disagree.....Those gaskets are junk, Harden & fail in short order. Use Hylomar M or Permatex form a gasket if pitting/corrosion is present.

 

[perfect_oil]

Originally Posted by clinebarger
I disagree.....Those gaskets are junk, Harden & fail in short order. Use Hylomar M or Permatex form a gasket if pitting/corrosion is present.


I used Permatex Ultra Black the last time because Victor Reinz quit making the thermostat housing gasket. Worked good.