Temp gauge fluctuating after coolant change...

[derekjl]

Not sure if it is considered normal, but my temperature gauge seems to be moving up and down every few minutes. Either it always happened and I never noticed or it just started happening. I had no service history when I purchased this truck, so I had the shop I normally take it to do a coolant flush. They also replaced the thermostat and gasket. I swear the gauge used to stay in one spot at all times after the truck was warm, right around 210 degrees. Now the gauge waxes and wanes. According to the gauge, the thermostat is opening around 225 degrees. When this happens, it then drops very quickly all the way down to 150 degrees or so, then it will creep back up to around 190 or so. When it does settle, it seems lower than it used to be, maybe 185 compared to 210 or so. I'm guessing there could now be some air in the system? I'm also still smelling some coolant after a few days, not sure if that is a bad sign. It's frustrating when you pay someone to do something and it ends up being worse than it was previously.

To summarize, is it "normal" for the temp to fluctuate? Does the thermostat open only once, or does it open/close many times depending on temp?

 

[Big Mama]

Sorry you’re having trouble. The thermostat should open and close slowly based in temp. The one in my boat, a 5.7, does the same thing bc my tstat is either all open or all closed. You didn’t mention your year and engine but you shouldn’t be smelling coolant ever. Check your passenger floor board for wetness from heater core leak. Air bubbles are common after a flush but they usually happen at a stop light not traveling. The shop needs to fix this. Unless there’s a problem with the temp sending system it’s too cold and should sit at one spot

 

[Doubeleive]

Temp should reach normal temp and stay pretty solid, could be air in the system, could be bad thermostat, could be bad temp sensor with the later being less likely if it eas fine previously, definitely should not be smelling coolant unless it was just some residual odor from the flush, keep an eye on the coolant resevervoir tank level and see if it changes at all

 

[drakon543]

my 97 stays pretty solid after the first the time thermostat opens. it will heat up to just past half then come back down to above 1/4. if im just cruising around it wont move from there again. if im pulling something up a large hill or im driving like an a**hole it will fluctuate a little but it stays between 1/4 and 1/2. when i bought it the thermostat was removed and the needle would barely move from the lowest mark. the thermostat i put in was a cheap one from advance. probably a cheap bwd or something. i didnt start using acdelco stuff until i felt the truck was worth better parts.

 

[trevcda]

The only time my temp gauge fluctuated like that was when I was low on coolant. Get a gallon of premixed coolant (or distilled water if you are in no danger of freezing or overheating) and dump it into the reservoir and see if your temp gauge doesn't even out. If it does, you will know that you were low on coolant. And that you will be again, especially if your are smelling it. Put a large piece of cardboard under the engine when you park it. This will help you locate where it's dripping from. Check your oil for foreign fluids and watch your exhaust for excessive steam. With any luck, you're just low and filling it will solve the issue.

 

[iamdub]

+1 on air bubbles in the system. Low on coolant means there's air in the system as well. On my '02 S10 (same basic layout as the '96-'99 Vortec V8), I'd back it into a shallow ditch to really get the radiator cap as the highest point, remove the cap and let it idle until the coolant was flowing good. The level would drop so I'd top it off with a bottle of pre-mixed coolant. After the coolant level was pretty stabilized, I'd turn the throttle with one hand to gradually rev the motor. The higher it revved, the more the coolant level dropped in the radiator. I'd pour in more coolant as I increased the RPM until it was around 4-5K RPM and hold it there while I screwed down the cap. As soon as I let off the throttle, the excess coolant would surge into the overflow. I'd top off the overflow and let it idle to ensure the temp gauge stayed normal.

 

[iCajun]

I had a similar incident. Air in the system and a radiator hose that was collapsing. Replaced the hose with one with an internal spring and finally got the air bled out.

 

[Big Mama]

For wife’s bmw I put the front on ramps or stands to get out bubbles but the bubbles show hot temp it doesn’t cover the cold problem.

 

[derekjl]

Just an update here. My father took the truck back to the shop that did the coolant flush and thermostat change. I guess they bleed the system. The coolant temp gauge is much more stable now, but it seems to open around 230 degrees when the truck is totally cold, it will then drop to about 160 and then rise and pretty much stay around 190 or so, two ticks below the 210 degree mark. It seems the most stable when cruising on the highway. Although I swear the heat is not has hot as it was before the work was done. I took my meat thermometer and the air out of the center vent once the truck is totally warm is 140 degrees. The only thing I'm concerned about is the thermostat opening that "late". The receipt says they did in fact use a GM OEM thermostat, but I guess it could still be one of those $3 ones. Thoughts?

 

[iamdub]

Those are symptoms of air in the system. Sounds like they didn't get it all out.