Really Slow Coolant Leak In A 03 Zr2 4.3

dougs01gt · April 2, 2011

Hey guys,

I have a friend with an 03 GMC ZR2 sonoma with a really slow coolant leak. So far he cant find where its going. He has 98,000 miles on the truck. Below are the knows with the issue.

1. No Coolant smell in the cab.

2. pressure tested to about 15 lbs and loses about 5 lbs in 5 mins on the tester.

3. New intake gaskets from the dealer less than 250 miles ago after dealer said the leak was the intake gasket.

4. No coolant present in the Oil.

5. He can sometimes smell coolant when he stands on the pasenger side of the truck in front.

There are no leaks present at all. even after using the pressure tester for 3 or 4 hours.

Thoughts? Thanks all.

txab · April 3, 2011

Look very very closely at the water pump and gaskets. You can have a leak and it will evaporate without dripping on the ground. Thoroughly go over the radiator looking for signs of leaks where the tanks are crimped to the cooling tubes. Traces of dried coolant may show up as a white substance. Check all hoses and fittings for small leaks. Was the coolant tested for any signs of combustion products?

dougs01gt · April 4, 2011

Look very very closely at the water pump and gaskets. You can have a leak and it will evaporate without dripping on the ground. Thoroughly go over the radiator looking for signs of leaks where the tanks are crimped to the cooling tubes. Traces of dried coolant may show up as a white substance. Check all hoses and fittings for small leaks. Was the coolant tested for any signs of combustion products?

I'll mention this to him. How would you check the coolant for combustion products? Smell?

Wingnut · April 4, 2011

That motor is renowned for intake manifold gasket leak of the coolant variety...But since you seem to have that covered, as well as no coolant in oil...I've got no idea.

txab · April 4, 2011

Look very very closely at the water pump and gaskets. You can have a leak and it will evaporate without dripping on the ground. Thoroughly go over the radiator looking for signs of leaks where the tanks are crimped to the cooling tubes. Traces of dried coolant may show up as a white substance. Check all hoses and fittings for small leaks. Was the coolant tested for any signs of combustion products?

I'll mention this to him. How would you check the coolant for combustion products? Smell?

I know NAPA has test strips that you dip into the coolant to check.. You can buy an additive that you put in the coolant to find leaks, Shows under a black light. I'd thoroughly examine all external areas carefully first

How much volume is this vehicle loosing and at what rate?

BlackZ71Silverado · May 23, 2011

I had an issue like this with my 2000 ZR2 Blazer. The coolant was going low and I could not finc the problem. It ended up being the radiator had a small, slow leak. It was cracked around the top on the plastic part (Don't know why they made them plastic?). It was hard to find but check around that area, that would be my guess. I also had no problems with a pressure test, it only leaked when the radiator got warm and the crack in the plastic would expand from the heat causing it to leak slowly.