Hi all. I'm new here to this forum and thought I would chime in with my current project.
We have a 2004 GMC Jimmy ZR2. This is a Canadian only model. We gave the vehicle to our daughter last year. It has had a small coolant issue for the past 3 or 4 years, however I had replaced the thermostat/gasket assy, since it was visibly leaking, and asked that she keep an eye on it. Well.........
Anyway it got low again, overheated, and blew the rest of the coolant out. They let it cool, refilled it and have been babying it ever since. A couple weeks ago she calls me and tells me it knocks very bad when she starts it. I kinda brushed it off, however she was persistent. I traded vehicles with her and sure nuff, start it cold and it knocks like a ol' 6.6 diesel conversion at 30 below. Well I'm just about ready to remove the heads. Everything else is off. heads and intake are going in for level and leak inspection.
Biggest bother is I could have saved all this trouble if I had taken the time to repair this properly long time ago.
As a side note this Jimmy has some of the worst fuel mileage of any vehicle I have ever owned. 17mpg hwy. Maybe it will be better after the rebuild.

 

its the lower intake gasket, coolant is getting in the oil and making the lifters noisy. im guessing your using dex-cool antofreeze? if so i would say to stop using right away. tear down the motor to the heads (remove upper and lower intake) replace old leaking gasket with felpro gasket kit part number FPG MS98002T. thats the metal one, best you can buy. and flush out the cooling system and use the green antifreeze, it doesnt deterioate the gaskets and seals, do anm oil change right after and you should be good as new!

 

Would this also put oil into the water and eventually water into the oil?

 

hope it goes well and it didnt roast the bearings

 

the knock sounds like the bottom end. I would say it ate the babbot material off the bearings if it has been run like that for a while, or if the coolant has been in the oil for an extended period of time. Pray it isn't into the crank bad and just replace the bearings..... or go to the local junkyard and pull one out of a blazer,jimmy,bravada,s-10, sonoma, so on and so on. They should only run about $110- $150 for a complete engine and then you got a whole bunch of spare parts off your engine currently in the vehicle. ????