The patient: 1992 Olds Regency 98 w/265,000mi. No SC, L27, nonDEXcool, aluminum UIM, aluminum water outlet neck.

The symptoms:
1. Coolant low (warning lamp) on every 100mi after topping up coolant.
1a. Coolant consumption higher at higher speeds.
2. Very slight sweet odor after accelerating WOT from 45 to 80 mph.
2a. No overheating. Temps normal at all speeds.
3. Oil level & appearance normal. Almost zero oil consumption between changes. No coolant in old oil at changes.
4. Coolant appearance normal, except for a few elongated black floaters
5. No pressure at rad cap when engine hot.
6. No apparent external coolant leaks.
7. Coolant recovery tank, when filled, is consumed and does not recover.
8. MPG remains typical 24.5 to 30.
9. Engine is original, and has never been opened up.

IM upper?, IM lower? Both? Heads or head gaskets? Other?

Thanks, Steve

Hmmm, hard to say on this one.

If it was the LIM gasket, it has 2 different paths to go in. Through the intake ports, or into the lifter valley and down into your oil.
UIM gasket, it would puddle in the valleys of the LIM and eventually get sucked in. Which, according to your chart saying, WOT=sweet smell. Then it'* possible its sucking it out of the valleys.

Based on the age of the vehicle, the miles on her and no other prior history of gasket changes, I suggest a triple gasket bypass. UIM, LIM, and head gaskets.

How'* your operating skills, tool inventory and nurses bringing beer?

Mike is right. If you are diving in there you should do all three ... LIM, UIM and head gaskets. Don't want to fix one and have another fail 1,000 miles down the road.

Thanks for the information!

Addl info to my initial post: I am getting some small oil puddling under intake bolt at front, driver side. I replaced plugs 2 mo. ago, 100k mi were on the Bosch platinums. 5 plugs looked normal; one had small noncarbon-looking deposit on ctr electrode insulator.

I have looked at gasket kits online, and some do not include new head bolts. Should they be replaced?

If the heads are off, I should probably repl valve seals and maybe guides (if replacable). This engine has never required any added oil between changes (6-7000 mi interval). It has been run on Mobil-1 for the past 200k mi.

Steve

Head bolts need to be replaced because they are torque to yield.

#5 plug might be an indication of coolant getting burned.

Sure, might as well replace those while you have them off.

Update: Leaking heater core is definitely contributing to the coolant loss. Coolant was apparently leaking to exterior of vehicle from the heater core, so was not noticed. I have continued to drive it (2k mi), keeping radiator full. A few days ago, the heater core leak suddenly appeared inside (soaked carpet).

I disconnected heater hoses, and made up a U-shaped bypass hose so I could continue to drive the car while replacing the heater core. It appears the coolant level has stabilized, but intake manifold is still a suspect.

Good catch, and a good temporary solution.

I am going to throw in my 2 cents worth here, even though you can't buy much with it. I am going to proceed under the assumption that no work has been done to the engine.

Head gaskets: If it ain't broke, don't fix it. They usually outlast the engine. I would need serious evidence to tell me that the head gasket has failed or is failing to have me even remotely consider addressing the fix.
Oil pooling: Likely valve cover gaskets. If oil leaks out the top of it, it will pool right on the intake manifold. They are a common fail point.
Coolant leaks: There is a coolant passage that runs between the upper and lower manifold on the drivers side, near the thermostat, that runs up through the throttle body. In my case, that was a failure point, and it was leaking coolant out. If it leaks in to the intake track, it will dump in to the first runner, which I believe is the upper right cylinder (could be lower left, which ever is further out). That didn't happen to me as there is a gasket that separates the runners on the plastic manifold.

Recommendation: 20 years and 265k miles is quite an accomplishment so far, if you have the know how and tools, do a LIM job over the weekend. I can certainly see the wisdom in some porting and polishing work too while in there. I would do the gaskets before they fail royally on you and dump coolant in to the lifter valley. You will also see other potential leak points that likely need to be addressed after 20 years, like the bypass fitting under the alternator (if not already done), the o-ring on the heater pipe on the passenger side, etc.

Oh, I would do the heater core first though with it leaking like that, and that job is not going to be fun.

Coolant loss was 99% heater core leaking. Oddly, found passenger rear floor soaked more than passenger front. Need advice on rmv-repl heater core.

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