Coolant leak -- mechanic can't find


We have a 1998 Chevy Express 15psngr van.

It has an obvious coolant leak. We believe that it only leaks when we turn the vehicle off. The peculiar thing is that sometimes it doesn’t appear to leak while other times we have a huge puddle underneath. We have a nice spot in the drive. We have also seen fluid pour out. Not just AC fluid. We have taken it to the mechanic twice and both times, they were unable to find the cause. I believe it is coming from the area around the water pump where the hoses connect. We told them this and today they looked at it again, and they could not find anything. I know that they have done the pressurized test and still cannot find anything. We are going to ask a friend to look at it for us as well. If he can’t find it, we will try a dealer.

Can anyone give us a suggestion on what to look at?


I would pay close attention to the intake gaskets. This was a common problem for GM.


The pressure test that allegedly was done would have had a gasket leak show up.


After you see this puddle (of orange or green coolant?) do you check to see if the coolant reservoir has drained or is very low?

Does the coolant temp gauge ever register hot to overheating?

Have you tried putting apiece of cardboard under the engine compartment to attempt to find the location of the leak?

You said you seen fluid pour out?

What type of fluid or color and if so, where did the fluid come from?

If you actually PHYSICALLY seen the fluid run out you should already know the location of the leak.


I disagree. Do to the design of the intake gasket (plastic with imbeded rubber seals) it is highly possible to pressure test the system and have the seal stay is place and not leak. Other times you can apply pressure to the system the rubber seal will shift and leak. The biggest factor in reproducing the leak is engine temperature. As the engine heats up the heads and the intake expand at different rates (cast iron / aluminum) if the engine is to cold or to hot when pressure checked it may not leak.


That’s fine. I don’t have a problem with that.


Here is how you can have a coolant leak that only leaks some of the time (and I have had this problem). I’m talking about the water pump. If the water pump shaft has a bad spot on it, and the shaft seal also has a bad spot on it, the pump will leak only when the car is stopped and the 2 bad spots are aligned. So if you stop the car and the 2 bad areas are not aligned, nothing will leak. If you stop the car and the 2 bad spots are aligned, it can gush. When the car is running it won’t leak or leak very little. The solution is replace the water pump.


'98 Chevy? I think Dartman nailed it. The plastic intake is the first place I’d look. They are indeed natorious for leaking. Expensive fix, especially if it’s not caught early. Not one of GM’s finest designs…