After trying to diagnosis my 99 5.7L yukon I check my oil and its a lighter shade than it should be and it seems the viscosity is also off. I also removed the radiator cap and started the car and anytime I would give it gas the radiator would shot out coolant as if gas might be escaping from the engine. So would these be conformation of a bad head gasket?

 

Is there oil residue in the coolant reservoir?? Is there any water on the oil dipstick when you take it out?

 

I'm not sure about the oil residue in the coolant reservoir, but there is something wrong with the reservoir to begin with. It did appear to have water with with the oil on the dipstick.

 

Considering everything is normal, there should be no oil in radiator, and no water in the engine oil @ all. Whether it is a head gasket or not is not a simple find. These diagnose procedures I would do first.

1. Do a compression check on all cylinders and write them down. All cylinders will not be exactly the same ( look for adjacent cylinders that are basically the same) telltale sign possibly head gasket.
2. Pressure test radiator & cap for @ least 1/2 hr. Pressure is stamped on cap.

The radiator also has transmission cooler internally which could present problem.
NOTE: The coolant tank must maintain NORMAL level, if not, find the leak. The heater hose on the front of the intake manifold has a locking clip that seals the hose, look for coolant @ that connection. Just a few suggestions for you.
David g.

 

It's been running extremely rough. I've had problems getting it to start, it usually wants to die when I do manage to get it started, and idles very rough. Plus smoke from the exhaust. It's had a history of overheating due to a bad radiator.

 

I second the compression test...

 

If you have coolant shooting out like a geyser when you give it gas while the cap is off or even just a kinda steady supply of air bubbles, then yes the head gasket is bad, what is happening is exhaust gases are coming back into the cooing system, you most likely will also have an excessive amount of white kinda sweet smelling exhaust coming from the tail pipe. with this you may or may not have an oil/water mixture problem.

 

If it has a history of overheating too that to me confirms the problem as head gasket, just overheating alone can cause the gasket to go, then with the other symptoms it is now having sorry to say my friend but I would say 99.9% sure its head gasket.