Canadian Hummer Club Forums

I'm sure it's been like this for a while but I am due for a coolant flush and thermostat change (my h1 has single T-stat) and wanted to know if it's normal for the temperature Guage to behave as follows.


At startup it's cold (160degrees) and then as I drive for a few kms, the Guage moves towards hot and goes slightly beyond 200 and then few seconds later it drops to around 170. Few more minutes of driving, it goes back up to 205-210 and then goes to 170 a couple of seconds later and keeps repeating the cycle of 210 to 170.....


Is it normal for the Guage to go up and down like this..170 then 205 and then 170 etc. Does the temp guage or T-Stat needs replacement?


My other cars stay at mid range and the Guage stays steady as I drive. I'm sure the coolant flows through the rad as needed when the car gets hot but the temp gages are steady

I have the single as well,

And when cold it will do that exactly, well mine reads 160 to 220, then fast drop to 190, A couple times, then semi even,

But once it's all warmed up should be semi steadier,

Like I mostly sit at 200, and lol up a long hill will reach 220, stay there for a bit and slowly go back to regular street driving


Your tstat is opening , but I'm not sure why yours is read cool, at normal stat would be at 190 ish-200

But hey, Tstat change is super easy, 3 bolts and bam she's off ,

Need tstat ( only the short black one, longer won't fit) and gasket, I didn't even drain anything, you can do in 10-15 mins with tools there,


Unless your polar bear , who just coughs and its in

This one is for ours

Crappy tire gave me this one and it's to long and bottoms out,

Won't fit

My dash is off by about 10 degrees but it stays pretty steady and will move very slowly between 200-210.
On the OBD port i am getting 195-204f which is a more accurate reading. Big fast swings in temp are ominous
but may be different on NA. Were i to see 40 degree changes on my truck the block tester
is the first tool i would grab. LOL

I'm assuming when the temp hits 210, the tsat opens and engine cools in a few seconds to around 170. It slowly creeps up to 210 and then it cools down to 170 etc etc.

My question is that shouldn't it maintain around 200ish instead of dropping to 170 and then kicking in at 210 to drop to 170 and then kickin again at 210.

Why the fluctuation. Is my tsat faulty?

For ME, once it's warm its steady at 190-210 depending if I'm on a hill etc, but the temperature jump is ONLY when motors ice cold, once it's warm it defiantly would be like your other car and be fairly steady after warmed,....


Hopefully someone can give more personal experience

I have the dual set up with the turbo. After warm up the engine will run at about 195 around the city. The fluctuations are only a few degrees. On the highway it will climb to 204 and hover there with a few degrees fluctuation depending on engine load. (hills etc)
The only time I see a real swing is when transitioning from highway speeds to city speeds or when in the mountains pulling long hills when the fan will pull in fully and drop the temp quickly to 195 again. 
 
Your thermostat should modulate its opening to maintain the preset temperature relatively stable....not cycle back and forth for city driving. 170 is likely a bogus reading for this time of year unless your fan clutch is boned.
 
GreenMeanie is correct in that the OBD port is the better reading. I have a Scan Gauge II plugged into mine and in real time it reads different from the gauge in the dash. 
 
Is your fan clutch ok? Is it seized into the engaged position? If your temp is falling that low this might cause this under light engine load if it does not disengage as designed. 
Did you compare the OBD reading? I would do this immediately. The Scan Gauge II is cheap and frankly awesome as it does so many things. 
 
Hope this helps.
 
Derek

I just purchased the scan GuageII. Let's check and see. Might get the tstat changed to 190 type when doing the coolant flush. I'm not sure what I have right now. How would I check the fan clutch if it's stuck

With the engine off and the truck cold give the fan a spin. It should have slight resistance but not freewheel. If it takes any real effort for it to turn...the clutch is seizing/seized.