So I had a mechanic replace my LIM gasket with the GM one and the upper with a FelPro now it appears that coolant is leaking externally out of the Intake plenum right by the thermostat housing. Mechanic says there is no way this should be happening. BTW this is 2000 bonneville SE. I know the coolant is leaking because the gasket is wet and I wiped the coolant down and now I'm running the engine and more is seeping out help!

Have you taken it back to the mechanic? I would definitely get it in front of him so he can see that he did something wrong.

I'm going to take it back to him tomorrow, but my question is, what could be causing coolant to leak externally from the upper intake right by the thermostat housing. We replaced the upper and lower intake gasket, coolant elbow, he used sealant on the lowers. It was not leaking coolant in the upper before the job

are you sure it is not the thermostat housing gasket?

yes because the UIM gasket is wet where it meets the intake surface and I can see coolant seeping out from between the gasket and the intake. It'* a very small amount but it'* still there.

Thanks, I'm hoping the surface isn't warped. Is it possible that just the Fel Pro UIM gasket is faulty? I paid 63 bucks for the GM lower gasket I should hope ot isn't bad right out of the box.

Is it possible that the new UIM gasket is faulty. Can it just leak externally on it'* own? Or does the LIM gasket have to be blown for the upper to leak?

It is possible for the new UIM gasket to be faulty, but not likely. And, no, the LIM gasket does not have to be blown for the upper to leak. The upper has its own coolant passages to provide coolant to the throttle body, and thus its own source for leaks. These passages are just behind the thermostat housing and between the throttle body and the UIM. As jr's3800 indicated, you may have a bad (warped) UIM that is causing the leak. If the old UIM got nice and hot and warped, the old gasket probably warped with it to compensate. Now that you replaced the old UIM gasket with a nice flat, new one, it leaks. Or maybe the problem is a bolt or two that he forgot to tighten...or overtightened....or stripped.

Thanks for all the replies. I'm leaning towards the UIM being warped. Does anyone know how much a new UIM costs and a good place to get one?