Hi, my father'* Olds 88 LSS with 3.8 VIN L-engine is having what seems like over heating problem. I tried searching the forum with no success, so here it goes:

Sympton:
1. Engine is shutoff by computer while driving (mostly while local traffic, sometimes on highway). Instrument gauges shows HOT temperature light, chimes once, but temperature gauge shows operating normally with needles around 200F mark.
2. When HOT temp light turns on, VOLTS and OIL PRESSURE lights turns on too.
3. Engine can be restarted right away, and sitting idly fine, but if adding too much gas, it will shutoff again.

Observation:
1. No coolant leaks. Flushed the coolant last night with Preston radiator flush and added new coolant, didn't help.
2. Upper radiator hose is hot, lower hose is about 20-30 degree lower, merely warm.
3. Stock T-state with 195F. Everything in the engine/cooling system is original stock item, car has 140,000 miles.

My thoughts:
1. Water pump is not functioning right, allowing too little flow of coolant. How do I know if this is the case?
2. Faulty temperature sensor in the engine. How do I know if this is the case?
3. Other possibility?

Thanks for the help.

Replace the thermostat with an 180 degree unit, specially in Houston.

NO!

The thermostat according the gauge is working 100% perfectly. No reason to change parts and spend money on things that are working fine.

Get the codes in the computer scanned. There are two sensors ...1 gauge and 1 to the computer. It'* possible the computer one is bad. However if the car is shutting itself off, then a code would be stored and tell you exactly where to start.

I'm gonna vote "Other possibilties"

You did all the manual checks correctly (hose temp). I can't think of any way to manually test the coolant temp to verify the gauges.

So, as much as I hate to say it, I gotta agree with Bill and suspect a bad sensor.

The reason why I mentioned the thermostat is due to the fact that GM issued TSB-99-06-02-018, Titled: Cooling - Thermostat Design Change. This TSB installs a lower temperature thermostat.

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Cooling - Thermostat Design Change

File In Section:06 Engine/propulsion System

Bulletin No.: 99-06-02-018

Date: November, 1999

INFORMATION

Subject:
Thermostat Design Change

Models:
1994-2000 Buick LeSabre, Park Avenue, Regal
1995-1999 Buick Riviera
1995-2000 Chevrolet Camaro
1998-2000 Chevrolet Lumina, Monte Carlo
2000 Chevrolet Impala
1994-1996 Oldsmobile Ninety - Eight
1994-1998 Oldsmobile Eighty - Eight
1998-1999 Oldsmobile Intrigue
1994-2000 Pontiac Bonneville
1995-2000 Pontiac Firebird
1997-2000 Pontiac Grand - Prix
with 3.8L Engine (VINs 1, K, L - RPOs L67, L36, L27)

There may be some confusion as to the correct thermostat application for the above mentioned vehicles when ordering a replacement part due to a design change for the 1999 and 2000 MY vehicles. The design change will affect service replacements of previous 90 degree V6 engines.

The new design will not fit previous 90 degree V6 engines due to a change in the position of the pintle and a different shape of the upper thermostat assembly. Refer to the following figure for identification of the current thermostat.

I think I saw something on this in my manual. The thermostat is slightly off to the side in the metal versus being in the middle if I'm correct. Minor difference to say the least.

Still don't think this is the thermostat. The gauge is reading that there is not a problem with it.

Reading this makes me want to have you check your temp sensor, but since I don't have my FSM'* with me to see how to exactly do that and not having done it before myself, I'll have to defer to someone who has and can help you check it out.

From reading your problem, it seems that you're not overheating, but your PCM thinks you are. That would make me want to check sensors next.