Agreed...but worth investigating. Now that I think more about it, the presence of oil on TOP of the LIM and the obvious leak at the side of the VC, along with the leakage not containing coolant, suggests VC gasket and not head gasket. However, the OP did report coolant loss with no apparent leak, and that coolant'* GOT to be going somewhere...either UIM or LIM.

Get out the toolbox!

Never rule anything out, but I'd prefer that the usual suspects be checked first. I'd still like to hear about the throttle body gasket area, as that is much more likely to be leaking than the head gaskets, and is right above the area he'* showing in the pictures. As is the thermostat, and the coolant temperature sensor. If that much coolant is being lost to the outside due to gasket failure, I'd expect to see more of a liquid in the picture of the top of the LIM. It'* hard to tell from the picture, but it looks as if that stuff has been there for a while.

Edit - one other thing that I forgot is that there is a rectangular cover on the driver'* side of the LIM that could also be leaking. It'* very hard to see as it sits below the TB, and behind the crossover pipe. You can see it (has the arrow on it) in this picture that Bill Buttermore took.

two bonnies, go back to Techinfo article 38 and scroll all the way to the bottom. You will find links to several pictorials for changing the UIM / LIM gaskets. The only comment I have is that it is safer to use a tungsten carbide gasket scraper to clean the crud off gasket sealing surfaces, finishing with brake parts cleaner to degrease. Abrasive discs make the surfaces look pretty but throw tiny bits of abrasive into the engine. Not a good idea.

Also, you can check out these links for an idea of the procedure. This is for a 2003, so there may be some minor differences, but it shows what needs to be done.

UIM

LIM

Thanks all. As I expected your comments are REALLY helpful.

I am now down to digging to investigate exactly what is leaking as I really can't tell from looking.

is what is really worrying me. I think that the obvious leak shown in the photos is the valve cover, but the drop in coolant with no leak anywhere is what has me really worried. I first thought the LIM was leaking and flowing down, but I'm not convinced of that anymore. I think the slick is from the valve cover.

I haven't replaced a valve cover gasket myself before (although I have replaced pumps, flushed coolant, replaced tensioner on this car). Is it as straightforward as

1. remove cover
2. remove gasket
3. clean area
4. replace with new gasket
5. put cover back on

Or is there something else I should know about the valve cover set-up?

My plan is to address the first obvious leak and then watch the UIM/LIM closely. Process of elimination. What really has me stumped is that the car does not have any other symptoms of the leaking UIM/LIM other than the collant drop. There is absolutely no hesitation, no noises, and it runs just fine.

From the pics above, I would say your LIM gaskets are causing the wicking up through the LIM bolts below the UIM, and your LIM end seals are leaking at the corners down the heads. Very typical.

Would you also say "just go ahead and replace the UIM"?

Manufactured 12/20/00. I am asking here about reusing the old parts and replacing just the gaskets.

This is where having experienced people helps. I thought the same thing but haven't dealt with this before. Will confirms my suspicions, although the leak at the bolt is neither all that fresh nor all that much, it still is a leak.

I replace the UIM on EK98'* car. It was manufactured in 2002. And it was already failing.

Ditch the UIM, go with aluminum framed LIM gaskets, Flush out the Dex and never put it back in, and replace your valve cover gaskets for good measure.

If you want to be prepared for all eventualities* with your UIM, LIM and VC, here is my recommended shopping list (with sources):

LIM gasket set, GM 89017816
http://www.rmsautoparts.com/proddeta...?prod=89017816
(Or can be obtained at GM dealer; this is the newest style, aluminum framed set)

Thermostat, STANT 45848 (180°) or 45849 (195°)
Thermostat seal, STANT 25273
Thermostat gasket, FELPRO 35595
Radiator cap, STANT 10331
Valve cover gasket set, FEL-PRO VS50080R
Valve cover grommet set, FEL-PRO ES72833
Injector seal kit, AC Delco 2171379
Oil filter, AC Delco PF47
http://www.rockauto.com/
(Use discount code from this thread…)
http://www.bonnevilleclub.com/forum/...ic.php?t=71169
(Or all these items can be gotten at local auto parts store and/or GM dealer)

APN UIM kit
http://www.automotivepartsnetwork.co...product=229679
(Easily your best bet in a UIM, as it includes UIM and TB gaskets, PCV adapter, and steel-sleeved EGR passage)

From your local auto parts store, get:
“Help” GM coolant elbow 2-pack (use the one with two orange o-rings)
Permatex “Surface Intensive” Blue medium strength threadlocker
Permatex Ultra Copper RTV
5 qts 10w30
2 gal Prestone “Extended Life” coolant
Brake cleaner and carb cleaner

Tools needed:
Socket set
Wrenches
Screwdrivers
Torque wrenches (good ranges are 25-250 in-lb and 20-200 ft lb)
Breaker bar and/or long pipe (for removing alternator!)
Something to scrape and clean gasket mating surfaces
Ramps or jackstands and chocks
Rags...lots and lots of rags


===========
All these parts will cost you about $400 to $500 (less if you have coolant, fluids/filter already, more if you have to buy tools); however, a shop will charge at least $800 for all this, and a dealer at least $1200. Furthermore, if you DIY, you KNOW you are using the BEST parts available, thus doing everything known to prevent UIM/LIM problems from happening again.

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* "All eventualities" does not include: head gasket leak or any other head problems, cracked or warped LIM, cracked or warped TB, vacuum hose leaks, fuel injector or rail problems, bad coolant hoses, leaky radiator, wiring harness or sensor issues, etc. You will need to check for all these things.