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Discussion Starter · #1 ·
My 91 sidekick has a fluctuating temp, rough idle and pretty bad mileage. If I'm accelerating it reads that it's running cold. If I'm not on the gas it still isn't at operating temp. But it will read hotter than if I'm accelerating. I replaced the thermostat the other day and it's still acting up. Any ideas?
 

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The temperature gauge sender on the dash is not often an indicator of exactly what the engine temp is. It is best to get an IR thermometer for an accurate reading - the temp gauge works off of voltage - so you may want to check the wiring to it. And make sure that your thermostat is correct for your car, with the proper gasket (either paper for the 1mm housing or the rubber o-ring for the 4mm housing) with the bleed hole toward the radiator, and that it's not floating around in the housing.
 

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I've read that you need to use a Suzuki stat. I did mine the other day not knowing this. Is there a way to know what gasket you need without taking it apart?
 

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Not to sound like a broken record, but there are a number of things you should check - engine timing, for example, which can be verified by doing a compression test (all spark plugs out, F1 fuse pulled, well charged battery and floor the gas pedal when you are cranking for best compression). Your car should get 150psi on a stone cold engine - 170 or more on a warm one. You should also make sure that your spark plugs are gapped to .028" (.07mm). Checking spark plug tips are a good sign of ignition - black, wet, etc. Also confirm that your check engine light is on with the key on, and off once the car starts. You may also want to see if you can get a code 12 from the ECU. Instructions here:
Check Engine Light
You will find a small white box with a black locking top dangling on 4 wires next to the battery - remove the locking top by pressing in the tab, and jump the blue/yellow to black wired pin with a metal paperclip.

Regarding your thermostat, you don't need a Suzuki one - any good quality, Stant or similar, is fine. The factory thermostat is 180*, although many of us have put in 195*, which is fine as well. When you open the thermostat housing, you will see that the thermostat sits in a small well - 1991 is a cross over year - some of the housings are only 1mm deep - in which case you use the paper gasket. Others (mine included) are about 4mm deep. For this, you will need a 5mm rubber o-ring that is attached to the perimeter of the thermostat - many thermostats don't come with this o-ring and you have to buy it separately. If you look here:
1991 SUZUKI SIDEKICK Thermostat
you will see that the 3 bottom ones (Stant, Beck/Arnley, etc.) have the rubber gasket, while the ones on the top of the page don't. You must make sure that the bleed hole in the thermostat is facing the radiator, and that you have burped the system well to get all the air out.
It is possible, of course, that you have some kind of blockage to the circulation in your cooling system, as well. What kind of heat do you have in the car? It should be great, and available fairly quickly.
 
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