My 1995 GMC Jimmy 4x4 4.3 has a major coolant leak at the rear of the engine. It dumps all its coolant out and it can be seen running down the front differential and drive shaft u joint. I am curious where everyone thinks the source of this leak is coming from?

The bottom of the bell housing is clear so I don't think it's the two freeze plugs on the back of the engine. I am curious if there is a heater hose connecting to the back of the block or if the lower intake manifold gasket can cause this leak? Previous owner said his wife overheated the car once and he replaced the water pump and thermostat.

Anything helps!!

 

Can you see the freeze plugs on the sides of the block? Are they leaking?

The lower intake manifold gaskets can definitely leak out the back of the manifold. Maybe you can see them with a mirror and a flashlight? I have an inexpensive borescope camera that connects to my phone and works great for stuff like this.

 

I would focus on the LIM gaskets, that's where mine leaked. Is there any water in the oil?

George

 

I would almost guarantee its the lower intake gasket, if its not your daily i would stop driving it, when these gaskets blow out they will wreck your motor. Definetlty worth checking the heater hoses for pinhole leaks, etc first but most likely the lower intake.


And heres what happens when you ignore a LIM gasket...

 

You could put a die in the coolant to help track the leak easier, but I would agree with those saying to look at the LIM closely. Time to look at what else you can upgrade when you change out the LIM. Things you should research are: Fel-Pro gasket kit upgrade/ so it won't re-occur soon,upgraded spider and new fuel regulator, and so on.

 

Tom, the freeze plugs on the sides of the engine are both fine. I bought a little mirror and will try to check the back of the engine tomorrow hopefully to see what I can find. Hoping it's just the lower intake gasket because I would have no issue replacing that if it fixes the truck.

George, I will check again tomorrow but I have not seen any water in the oil. Again, hoping its the LIM gasket that would be a simple fix.

Alexei, I have not driven it since buying it. I had it trailered home with a massive coolant leak and have been meaning to work on it for a couple of weeks now. It wouldn't make it far even if I did try to drive it - it would probably lose all of its coolant in the span of 10 minutes. Ill look at the heater hoses running to the heater core tomorrow. The oil in the pan isn't mixed so I am sure the rest of the engine is fine if its the LIM leaking.

Jim, I thought about that but probably will try to look around with my mirror and phone first. I'm really hoping it's the intake. The previous owner thought it was a cracked block or head gasket but those both seemed unlikely especially with this engines proneness to intake gasket failures. Ill look into those things you mentioned.

 

I would suggest that even if it is not the LIM gaskets that you consider replacing them anyway as a preventative measure. As soon as I learned of how they could ruin my motor, I did them.

I'm attaching what many consider to be the best write-up that was on the web. But the link is bad so fortunately I kept a pdf of it.

 

Thats awesome to have! Thank you so much!

 

Be sure to use the Fel-Pro upgraded gasket kit for this project. They are more expensive but worth it. Good time to invest in the upgraded spider assembly , too. As Christine says-- this coolant dilution can quickly destroy your engine, so don't put it off !

 

Ok I have an update. So I was finally able to pull the lower intake manifold. The LIM gasket doesn't look like it failed. Could I still have a major water leak without any noticeable breaks in the gasket with the LIM off?

Or should I start looking at the head gasket/rear freeze plugs?