Temp Gauge readings

[cubano112266]

Hello Group,

I have a 1992 Metro 1.0 liter for now 3 years. This weekend after an 80 mile drive (all highway) the temp gauge read just at the middle of the range. Once I got off the expressway and drove through some local street to get to the final destination, I noticed that the gauge was reading in the top end of the range. I would say that it was in the top 80 % of the range, but never got into the red area and once I started driving again it shortly returned back to the middle of the range. I did notice that it only read high during a stop at a light or while stopped in traffic. Is this normal? Also, at what point does the radiator fan turn on? All advice is appreciated.

Thanks

A

[Woodie83]

The fan turns on before the gauge moves, your gauge should never move from dead center, even in a summer traffic jam with the A/C on. The switch that controls it is mounted on the thermostat housing, I think there's a relay in the box by the battery too.

[doug2060]

I have a 1991 metro 1.0 3cyl. I bought it back in January and it always does this. It will go to around the 80% mark then the fan kicks on and it will return to the center. It doesn't do it constantly but after starting it does it and if I sit at a light etc. I have been driving it pretty heavily since I got it and just assumed it to be normal but feel free to correct me on this as I have though about it being a possible issue.

[91Caprice9c1]

Well it's not normal, thats for sure. You're putting undue stress on things allowing that to continue, doug. With these little motors, all it takes is one trip to the redzone if you aren't careful and there goes your head gasket.

Cubano, Woodies spot on. Check your coolant level, test your rad. fan relay, and test your radiator fan.

Test the radiator fan by jumping it directly to the battery. If it doesn't spin, replace it.

Testing the relay:

The relay will have two pairs of parallel blades, one pair should connect the other pair when voltage is applied to them. Jump one pair to the battery, if it doesnt click, jump the other pair, if it still doesnt click, replace the relay.

When you find the pair that causes a click, get out your ohm meter and probe the opposite pair to test for continuity. If you read an open circuit or OL, or if resistance exceeds one ohm, replace it.

If the rad. fan and relay check out, replace the switch in the thermostat housing.

-MechanicMatt

[doug2060]

I'll be sure to do that TODAY. I do know that the coolant level is good and the head gasket was replaced in December along with a valve job etc. The fan does kick on and works properly but only when it reaches that point which is still well out of the red. I'll test the relay and the switch on the thermostat first. Would the water pump be a possible culprit as well? I have been making plans to replace it for the heck of it but will make it a priority if recommended. Thanks for the heads up. I was assuming because of the small size of everything that it was normal when it did that. Good thing this post came up...

[Woodie83]

Water pump is not your problem as it cools down nicely when the car's moving or the fan's on. Wait until it starts leaking, or you need to replace the timing belt. If your fan is coming on there's no need to check the relay or fan motor, your switch is just triggering at too high a temperature. My experience is that it should trigger before the gauge moves, but if it's doing this reliably it's probably no big deal. Maybe a different switch would trigger earlier. Also possible there's some air in your system, let it idle with the radiator cap off until the fan kicks on five or six times, can be hard to get all the air out sometimes.

[cubano112266]

Originally Posted by 91Caprice9c1

Well it's not normal, thats for sure. You're putting undue stress on things allowing that to continue, doug. With these little motors, all it takes is one trip to the redzone if you aren't careful and there goes your head gasket.

Cubano, Woodies spot on. Check your coolant level, test your rad. fan relay, and test your radiator fan.

Test the radiator fan by jumping it directly to the battery. If it doesn't spin, replace it.

Testing the relay:

The relay will have two pairs of parallel blades, one pair should connect the other pair when voltage is applied to them. Jump one pair to the battery, if it doesnt click, jump the other pair, if it still doesnt click, replace the relay.

When you find the pair that causes a click, get out your ohm meter and probe the opposite pair to test for continuity. If you read an open circuit or OL, or if resistance exceeds one ohm, replace it.

If the rad. fan and relay check out, replace the switch in the thermostat housing.

-MechanicMatt

Caprice/Woodies,


Thanks for the advice. I will have time this Saturday to check fan, relay and switch. I will post updates.

Thanks

[GM Line Rat]

Originally Posted by Woodie83

Also possible there's some air in your system, let it idle with the radiator cap off until the fan kicks on five or six times, can be hard to get all the air out sometimes.

One of the better methods of getting nearly all the air out of a cooling system that Doesn't have a "purge valve" in the cooling system (AKA Geo Metro) is to park the nose (front) of the vehicle on a hill or on a set of car ramps, remove the radiator cap and run the vehicle as woody stated until the fan kicks on several times. Parking the vehicle with the front higher than the rear promotes the Air in the cooling system to rise to the highest point and escape while it's being circulated in the cooling system .....which in this case would be the top of the radiator (Where the cap is) .....Remember, turn your Heater ON while doing this in order to purge any air out of the heater core also. If this fails to cure the problem and your cooling fan is kicking in when it's supposed to.......I'd suggest you consider giving the entire cooling system a good flushing out, and replace with NEW green Anti Freeze in a 50/50 mix, slighly higher (60/40) if you drive the car alot in near Zero Temps during the Winter.

[cubano112266]

Thank you GM Line Rat.

I might have not gotten all the air out of hte system when I repalced the Water Pump and T-belt two weeks ago. I will have it up on ramps first thing Saturday morning.

Updates will follow.

cubano

[doug7x]

Hey, kind of related...my temp. gauge quit reading a few months ago ('95 1.0)...which sending unit is for the gauge? (the one for the ECM & fan is working fine) Thanks...Doug

[doug2060]

I went out and unplugged and removed both temp sensors and the fan switch. I cleaned them thouroughly with carb cleaner (some white corrosion). I also noticed inside the temp sensor and fan switch connectors there was old motor oil. I cleaned those out as well with carb cleaner. I also checked all the relays and even cleaned them too for the hell of it. I let the air out of the system properly ( I got a few bubbles but possibly just from removing the sensors) and I think thats all it needed. The guage barely leans a bit to the right and the fan kicks on. You may want to try this too before going out and spending your money. Good luck...