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Pete, GMC Technician
Category: GM
Satisfied Customers: 29116
Experience:  14 years GM dealership technician and training.
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I have a coolant leak on my 99 gmc yukon and can not seem to find it

Customer Question

I have a coolant leak on my 99 gmc yukon and can not seem to find it
Submitted: 6 years ago.
Category: GM
Expert:  Pete replied 6 years ago.
Hello,I will be glad to try and assist you with this,Welcome to Just Answer.


I just need a little more info to assist better.

Can you tell me what size engine is in this vehicle?

Has the coolant system been pressure tested?

In what area is the coolant leak noticed?

Let me know so we can continue,Thanks Pete!
Customer: replied 6 years ago.
The engine size is 5.7 vortec, it hasn't been pressure tested and I notice the coolant leak coming from near the back of the block. I've talked with a couple people and they say it's the freeze plug but I though something else would happen if that was the case.
Expert:  Pete replied 6 years ago.

With this engine the most common leaks I have found for coolant near the rear of the engine or under the engine is usually either the lower intake leaking coolant (most common) or the freeze plug,usually the freeze plug that was removed and where a block heater was installed.

If you have a black heater inspect this it should be on the drivers side on the back of the engine.This can leak slowly or rapidly depending on how bad the leak is.

If the pressure test makes it hard to pinpoint the leak then you can purchase some coolant tracer dye at a parts store and add it to your coolant,then drive it for a couple of days of possible then use a black light or dye tracer light to inspect the engine over to locate the leak.

I have had to replace both the intake gaskets and the block heater to fix this type of leak here.

Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!