91 Grand Am overheating

My Grand Am ('91, 2.5L LE, 100k miles) overheats when idling or in stop and go traffic. Engine cools fine at speeds over 35 mph. Lost coolant the first time it happened, filled it up 2 times and now all the air seems to be out the system. Checked the fan, it does not work when the car is at 230F, while normal operating temp is 160F (maybe 180F not sure), but the fan motor works if directly connected to battery. Tried to check relay, found 4 on the firewall, one with wire colors almost (LT GR instead of DK GR) matching wiring diagram, pulled it out and checked it. Relay switches if + is connected to terminal 85 and - to terminal 86, Hayes says the relay should work with the opposite connections, but it doesn't do that. Checked all other relay's, 2 work either way, 1 works as the first.

I'm just confused, am I checking the good relay? How are they supposed to work? And what would be next?

All input welcome. Thanks!

And just out of curiosity, I have a Fuel pump relay, a A/C relay and a coolant fan relay, what does the fourth one do?

Reply to
Baudolino
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Shorted the 2 switched relay ports, fan started without a problem. Checked the input ports (one hot when car is on, other from ECM), 13.6 V constant, meaning ECM line is 0V So, the relay is used in kind of an opposite way in the Grand Am, explains the differences with the Hayes manual and shows the relay isn't the problem (with test results from last posting). Started the car and hoped the voltage would drop at operating temperature (160F), but it didn't. Kept the car running upto 200F and still nothing. My understanding is that the ECM should turn 12 V on the wire for the fan to start and this doesn't happen. Anyone experience with this? Do my conclusions make sense, or do I miss parts of puzzle?

Thanks in advance!

Reply to
Baudolino

"Baudolino" wrote

Actually, I believe the ECM provides the ground for the relay. Sounds to me as though you are missing one hot wire. Of the four wires at the relay.....you should have one large red wire that is hot.....a large black wire that goes to the fan.....a small brown wire that is hot, and the green with white tracer (I think) or just the green wire that is the ground signal from the ecm. So you need to see two hot wires at the relay connector.

Ian

Reply to
shiden_kai

No wonder I couldn't fix my Regal's fan. It's opposite of what I thought at the time. GW

shiden_kai wrote:

Reply to
Geoff Welsh

Did some checking, and the ECM is the ground. At coolant temperatures above

230F, the ECM breaks the link, no power on the relay, relay switches and the fan starts working.

The following wires come to the relay Red (30) -> always hot (to power the fan) Brown (85) -> Hot when car is on Green/White (86) -> Ground through ECM (no ground above 230F) Black (87a)-> To fan

Under 230F, the ECM provides ground, so there is power on the relay coil ->

the relay switch is open -> No fan If the ECM breaks the ground, the relay switch closes -> Fan goes on

So, after all, my car works as supposed, it just doesn't have enough cooling power on hot days. Hopefully it's just because of the engines' age and no crack in the cylinder head or something. For now I'll just put a switch in the ECM wire, so in summers I can make the relay 'think' the engine is always hot.

Well, at least Haynes was right about the fact that their was a relay.

Thanks for the input!

BTW According to this theory, if the car is of, there is no power through the relay, switch closes, fan should go on whatever the engine temperature is. It doesn't, so is there another switch in the system?

Reply to
Baudolino

"Baudolino" wrote

You have it all correct, except the ECM does not ground the relay below 230F (or whatever temp it turns it on at). The relay "turns on" when the green wire is grounded. The ECM will apply a ground to the green wire when the engine reaches the temp that signals the ECM to turn on the ground. So if you happen to have the ECM providing a ground at the relay below the turn-on temp at the green/white wire, something is not right.

Ian

Reply to
shiden_kai

That's what I thought, but I have a 13.5V difference on the ECM wire and the hot wire in cold run, and the relay is closed in this situation. If there would be no ground on the ECM wire, the fan would run. It really makes me wonder who designed that system, it's the '91 Grand Am, maybe they updated it in later years. That's why I hate electrics, they never work according to the book and always have the weirdest solutions to problems.

Reply to
Baudolino

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