I've had my Bonneville for about three weeks, and it'* been great. It still has the original UIM, so I've been checking my fluids often just to make sure everything is working fine. Today, I noticed a white milky buildup on my oil cap. The oil on the dipstick looks fine, and the car runs normal. The coolant level has been pretty stable since I started driving the car. Could this be a sign of the UIM failing, or possibly just condensation from the cold weather?

Thanks for your help.



The cap is almost completely covered with that white gunk.

Whip it off and keep watching it. Chances are it'* condensation inside the valve cover. A good way to check to see if your UIM is failing is to remove your throttle body and look inside where the EGR tube comes up. Do you see any coolant there?

I wiped off the cap and took the car to college today, and after class I checked it. The white stuff was back. I also noticed my coolant had gone down some (enough to notice). The engine sounds a little rough.

When I got home, I took off the throttle body. I found coolant in all the areas I circled in red.


UIM with throttle body removed.


A closeup of the TB.


I think the UIM looks pretty good around the tube.

Does all of this look normal?

The area you found coolant is normal. That is where the coolant flows to the throttle body. The tube just inside the UIM is the area where you don't want to see coolant. And in your case there is none. This does not completely rule out the possibility that it'* not condensation. The reasoning behind this is your dipstick oil looks normal. If that looked milky then I'd say you most likely had an LIM gasket failing.

By the looks of your UIM and the coked up pipe with no air gap, your UIM has not been changed. Because of the way it looks and you being concerned about it. I would suggest preparing to change the LIM gaskets, UIM manfold and gaskets. This will correct the potential of an LIM gasket failure as well as a potential UIM failure.

In addition to what Bill said, I suggest pulling the plugs and inspecting them. If you have coolant getting in to the cylinders, that will tell you.

This might sound dumb, but what will they look like if there is coolant in the cylinders?


...When I pulled the boot off the first plug, the whole end broke/fell off. It looks like the plugs should have been changed a long time ago, so I'm already glad I checked them.

You may see a glazing or fowling of the plug.

If you do replace the LIM gaskets and UIM assembly make sure to replace the 2 90degree elbows on the passenger side they are real bad about breaking and leaking coolant. Also a PCV valve replacement would be a good idea.

95-99 Bonnevilles with Series II motors used only one elbow. The other was cast as part of the alternator tensioner/bracket. The second elbow appeared in 2000 with the change of the alt bracket.

Sorry about that i get my Bonneville'* ang Grand-Prix mixed up sometimes.