the stupid "engine" light

[pollock]

In the last week my "engine" light has been coming on. I suspect the car is overheating (now that it's 100° here) but I guess there's no way to be sure whether it's a water temp or oil pressure problem.

I did a coolant service and that didn't help.

Last night I unplugged the temp sensor and started the car, expecting the light to come on automatically. It didn't.

So, does that mean I could unplug the temp sensor and drive it, and if the light comes on, the issue is with oil pressure?

[Grandmarchris]

What year is it? I think any year after '88 the check engine light is more of a replace engine light.

[pollock]

It's an 89 Grand Marquis, only 64K miles. I'm pretty sure it's a temp issue.

The light came on once at idle w/ AC blasting, and then another time on the highway with AC blasting. Then we got home and the car sat for about 15 minutes. I went back out and started it, and the engine died almost immediately. That was Sunday. This morning I started it and it seemed fine.

[gadget73]

the red replace engine light is either no oil pressure or severe overheat, like over 240 degrees. Overheat would show up steady, low oil pressure would likely flicker at stops and go away with some engine rpm. Problem is, if its way hot, the oil will thin out and drop the pressure. Sounds like yours is overheating. Put a temperature gauge in and see what its doing.

[mrltd]

I'd check the fan clutch or thermostat.

Unplugging the sensor doesn't turn the light on. Grouding the wire that was on the sensor would. The sensors are actually switches, that are normally open and close when the reach the set temp/pressure.

[pollock]

Yeah, in all cases where the light came on, it was in "hot" driving situations. It has flickered some, but I think it was after the light had been on for at least several minutes.

I borrowed the Autometer temp gauge out of my mustang last night and will put it in the merc tonight.

How do you check a fan clutch, other than to spin the blades and watch it slow to a stop?

What thermostat do these cars have from the factory? 195°?

[mrltd]

yup, 195.

Spin the clutch when the car is HOT and turned off. If it spins more than one revolution it's shot. Also, another way to see is just look and see how much goop is on it.

[pollock]

It's pretty grimey, but maybe not out of line w/ the rest of the engine compartment.

I'll hook up the gauge tonight and go for a drive, and then check the fan clutch.

Of course, a storm blew in and it cooled off to 70°, so an overheat may not be possible tonight. Figures.

[86VickyLX]

it should still overheat if it's bad enough. When's the last time you replaced your thermostat? I also had a bad fan clutch, and the car would overheat after a set amount of time. But this was just sitting, when are you overheating? If you are moving fast like highway speeds, the car moving that fast should cool the engine, that is if your radiator isn't clogged.

[pollock]

Hooked up the gauge and drove a combination of city and highway for about 20 minutes, AC on. It got a hair over 210° but wouldn't go higher. I would expect this engine to run less than 200°, probably less than 190° when it's this cool out (low to mid 70's).

Afterwards I checked the fan clutch. It would spin right at one revolution, which seems suspect to me.

The times when it has (apparently) overheated have been split between idling and highway driving.

I have not replaced the thermostat, but have only had the car for about 5000 miles. I would guess it is the original thermostat.

I'm going to drive it to work tomorrow, when it should be warmer, and see how it does.

[87vicFIVEO]

What year is it? I think any year after '88 the check engine light is more of a replace engine light.

Until 1996 that is.

[gadget73]

Depends what sort of light you're talking about. The red light in a 79-89 Vic/GM is for oil and temperature only. its completely and totally not related to the ECM. Some 1988 and all 89+ models had an amber computer 'check engine' light that would trip on a computer fault. The red engine light of death went away on the Vic/GM in 1990. Starting in 1996, the check engine light became grounds for inspection failure, but its still a computer controlled lamp.

[pollock]

Just drove it again, and let it idle for a while. Got it up to 225°. Spun the fan clutch and it went about 1.25 turns. I think I will go ahead and replace the clutch.

Does anyone know what water temp would trigger the factory engine light to turn on?

[86VickyLX]

Just drove it again, and let it idle for a while. Got it up to 225°. Spun the fan clutch and it went about 1.25 turns. I think I will go ahead and replace the clutch.

Does anyone know what water temp would trigger the factory engine light to turn on?

That's pretty high, normal operation temperature is around 195*- around 210*
Hope it didn't affect the engine at all

[1987cp]

Doubt anything will actually be damaged at 225 degrees, but running much over 200 isn't a particularly good thing, either. Which reminds me, I need to get some clear hose and locate a suitable clean container so I can siphon out a bunch of my coolant so I can swap in a lower temp 'stat for summer without having waste coolant to dispose of.