Coolant Fans / Temp Guage

[RastusMcNair]

I recently purchased a 2000 Silhouette with 29810 miles. The engine temp guage would never go more than slightly higher than the 1/4 mark and usually would run just below that level. That, combined with an exhaust backfire between 45 and 65 mph and poor heat, led me to believe the vehicle was not running in "closed loop".
I replaced the thermostat ( NOT fun) and the coolant temp. sensor. The guage now reads about half way between 1/4 and 1/2, closer to 1/2 if I get on it. Not surprisingly heat has improved.
My concern is that the cooling fans come on around the new temp. When this happens, even at highway speeds, the temp guage drops to zero. When the fans stop the guage resumes it's normal position. Also, when this occurs at a zero throttle position like a slow coast, the idle surges. Kind of a surprise when you are slowly rolling into a parking spot and the van accelerates.
I carefully bled the system, both cold and again at operating temp. Heat is consistant.
Is this an indication of another issue or just a Silhouette trait?

[RastusMcNair]

It's been a couple days and no reponses. Okay. How about this. On your Sil. when the radiator fans come on, say in traffic or at a drive-thru, does your guage drop below "C" or give a continuous reading as the temp. lowers?

[merc81]

On my 99 silo, the fans kick in one at a time, the first after the temp is past halfway on the gauge. When running, the fans cool things down fast, but never below 1/8 on the guage.

Hope that helps.
John

[rockwood84]

running on highway the temp gauge should stay around 1/4 mark.heavy traffic or long redlight it will get up too a little over 1/2 then the fan should kick on if it goes up little more the second fan will kick on it should go back toward 1/4. if your still sitting still the gauge will creep back to over 1/2 then fan should kick on.how much antifreeze do you have in it? an 80 % antifreeze 20%water will make it run cold. get it checked as sounds like you have it protected to 40 below 0. you need to find out what is causing the backfire as them intake gaskets do not like backfiring. it will crack the plastic they are made of.

[merc81]

I think you said that backwards; 20% antifreeze-80%water will make it run cooler; antifreeze has a lower specific heat content than water--straight water will carry away more heat than any mixture of glycol & water but it will freeze.
Read the mix chart on the bottle and put in just enough to make sure things don't freeze up in your area. Straight antifreeze and no water will overheat, most of us just use 50/50, but less antifreeze will make the coolant more effective. Of course, if the thermostat is working, the temps won't change at all.

John

[RastusMcNair]

Okay guys. Nobody has actually answered my question.


When your fans come on does your temp guage go "Flat"? Needle below "C" as if the guage had no power.

And do your engine RPM's increase during fan operation? Mine does. Other FWD vehicles I have owned did not do this.


The guage "trick" is really just a distraction. The engine surge, especially if slowly rolling along in bumper to bumper traffic, is troublesome.

[rockwood84]

merc81,what i said is that if you put 80% antifreeze and 20% water you will not make any heat to blow out the vents .in other words it will run cold in the winter . where as a 60% antifreeze 40% water will give some heat but not as much as 50/50.

[merc81]

Ok, yea rockwood84, I see what you're saying. As to the orginal question above, RastusMcNair, I did say my guage goes down very quickly, but never below 1/8. Nothing that looks like a short in the gauge.

I'd start looking at the power/ground distribution out on the fuse block above the battery. That's where the fans get their power from and it sounds like they are presenting quite a load to the available power source.
Do you have a diagram for that wiring? I have the books for my 99, not sure how much they may have changed.
John

[RastusMcNair]

Hi all,
Just a followup. As time went by this problem occured less and less until now it does not occur at all. The guage and fans opperate in a fashion I would expect.
I never did identify the cause of the odd operation. An air bubble working it's way out? The computer readjusting following replacing my bad thermostat? Who knows. But it did work out.