I have a non-supercharged 99 Bonneville which is consuming coolant. UIM failed and the eng. hydro-locked 43,000 miles ago, had it repaired at the dealer which consisted of a UIM change. It'* now consuming coolant at a pretty alarming rate. I just received the APN brand UIM and still need to get the Metal LIM gasket kit.

As far as applying sealant or RTV goes, does the EGR replacement tube require any sealant when it is installed? And Does the LIM gasket require sealant on the actual seals of the gaskets?

Any help would be greatly appreciated. Thanks

No RTV is needed on the UIM gasket. Install that gasket dry.

The only place you need RTV is on the LIM rail seals. (Sorry, I don't have a pic handy). Where those rail seals meet the head and block is where you need a generous dab of RTV. Make sure to get all four corners. It'* fine if it oozes outside of the engine, but keep it away from the inside counter balance cavity.

See where the orange tracing comes down to meet the block end seals (black rubber)? You put a dab in that corner BEFORE gasket placement, then tuck the gaskets in right, and put another small dab.

Ignore where I went all the way across the block end seals. The LIM I was about to install (last winter) had several scratches on the bottom surface.

Thanks for the info. I'm surprised the RTV wouldn't go all of the way across the block. So just the corners is enough unless I scratch up the surfaces.

99% of the time, all the way across isn't necessary. The endblock seals are very flexible and ribbed on the long axis.

S2 are slightly different, but very similar (this is a Series 1 L67 you're looking at here).

Thanks for your help. It looks like I don't have anymore excuses, I'm gonna tackle it.

Thanks again. A little extra insurance with the RTV couldn't hurt.