Big Temp. Gauge Changes After Coolant Flush!

[rs250]

Hey all, hope someone may be able to shed some light here.

 

2003 Silverado 4.8L.

 

I have a 147K and have flushed and refilled before but was doing more routine maintenance the other day.

 

I drained and refilled with distilled water, and then drove it around and then drained and refilled again with distilled water and then finally drained and removed ALL hoses and thermostat and replaced every single hose and thermostat with NEW GM AC Delco replacement parts.

 

I then refilled with fresh 50/50 pre mixed Dex-Cool and tried to burp the system best I could.

 

I have now put about 100 miles on it and I think whatever air bubbles may have remained should have worked themselves out. I did top off the reservoir ever so slightly with distilled water when it was cold to bring it to the FULL COLD line.

 

I am now getting really off Temperature gauge readings. The truck will warm up pretty normal and go to where it always has, just below the 210 mark. the truck has ALWAYS sat there during normal operations since new.

 

Now it will warm up to just under the 210 mark, and then after a while will drop a bit quickly and then after a few minutes will almost instantly go back up...sometimes it happens in two distinct "steps" on the gauge movement.

 

The coolant in the reservoir changes about a 1/2 inch from cold to hot (higher when hot). Truck is not getting hot or running abnormally. It us about 65 degrees outside right now. I am driving a 1000 miles roadtrip this week so will keep and eye on it and see if it works itself out BUT...

 

Is this a sign of a faulty (new) thermostat...just needs driving time to work out any other air??? Something else??

[Jsdirt]

Could try cranking the heat on high & going for a drive. Could be an air pocket in the heater core or hoses. Usually the up/down fluctuation of the temp gauge is normal -- just says your thermostat is doing what it's supposed to do. You might have been used to a non-functioning thermostat before you changed it.

[Nytemare]

Could be a sign that your temp sending unit is getting bad..keep an eye on it. Chances are its either the thermostat doing its job, or your sending unit.

[rs250]

Could be a sign that your temp sending unit is getting bad..keep an eye on it. Chances are its either the thermostat doing its job, or your sending unit.

 

Yeah I thought it could be the sending unit...but seems real odd that it would happen at the same time I did cooling system maintenance....hmmm My oil pressure gauge has also just started to act up, where on long highway drives at steady rpm it will move very slightly back and forth between two lines (very minimal movement, and real fast) ...this just started happening and I suspect the sending unit is getting old.

 

JSDIRT: Good idea on the heater...I did try that last night for while thinking that could help...I may need to run it longer...I am going from Phoenix to LA and then up to Sacramento tomorrow during a major rain storm so I should be able to give it a good run/workout.

 

The original thermostat seemed to be just fine, maybe this new one is just more sensitive??

 

Only time the old one would budge would be say if you were on a long uphill pull during cool weather, and one you made the top of the hill and then got off the gas going down the other side and the temp gauge would drop a fair bit and then the stat' would close and things would go back to normal.

 

This truck has been so damn bulletproof these little things that are just starting to pop up kind of get to me!!

[Nytemare]

Could be a sign that your temp sending unit is getting bad..keep an eye on it. Chances are its either the thermostat doing its job, or your sending unit.

 

Yeah I thought it could be the sending unit...but seems real odd that it would happen at the same time I did cooling system maintenance....hmmm My oil pressure gauge has also just started to act up, where on long highway drives at steady rpm it will move very slightly back and forth between two lines (very minimal movement, and real fast) ...this just started happening and I suspect the sending unit is getting old.

 

JSDIRT: Good idea on the heater...I did try that last night for while thinking that could help...I may need to run it longer...I am going from Phoenix to LA and then up to Sacramento tomorrow during a major rain storm so I should be able to give it a good run/workout.

 

The original thermostat seemed to be just fine, maybe this new one is just more sensitive??

 

Only time the old one would budge would be say if you were on a long uphill pull during cool weather, and one you made the top of the hill and then got off the gas going down the other side and the temp gauge would drop a fair bit and then the stat' would close and things would go back to normal.

 

This truck has been so damn bulletproof these little things that are just starting to pop up kind of get to me!!

 

Could be the start of issues with the gauge cluster too...the stepper motors on them aren't good you know.

[rs250]

Could be the start of issues with the gauge cluster too...the stepper motors on them aren't good you know.

 

 

Hmm, I think I have read about that before...if that is the cause, do swap out the cluster and lose the data, or just replace the stepper motors? How does the stepper motor manifest itself? Is it what I am describing or usually all out failure?

[Nytemare]

Could be the start of issues with the gauge cluster too...the stepper motors on them aren't good you know.

 

 

Hmm, I think I have read about that before...if that is the cause, do swap out the cluster and lose the data, or just replace the stepper motors? How does the stepper motor manifest itself? Is it what I am describing or usually all out failure?

 

When I bought my truck the motor was gone on my speedo...sometimes it worked fine...sometimes I was doing 200km/h in slow moving traffic.

It twitched now and than when it was "working properly".

 

The procedure is, the tech re-programs your new cluster with the Odo reading off the old one...than pops it back in.

I would leave it alone for a bit though....and get a Scan tool hooked up so you can log the activity of your sending unit..or you can replace the sending unit, its only 20 bucks.

 

You didn't nick a wire when you were replacing everything did you?

[rs250]

You didn't nick a wire when you were replacing everything did you?

 

No, I don't think so...I actually made my brother do a lot of the hose replacement in his shop ( he is a FAR better wrench than me )

 

I just read a thread on the clusters and replacing the stepper motors...sounds common and probably what may be going...considering I have an 03 and it is quite common, also since I am nearing a 150K!

 

Thanks for the advice, I will keep an eye on things!!

[Nytemare]

You didn't nick a wire when you were replacing everything did you?

 

No, I don't think so...I actually made my brother do a lot of the hose replacement in his shop ( he is a FAR better wrench than me )

 

I just read a thread on the clusters and replacing the stepper motors...sounds common and probably what may be going...considering I have an 03 and it is quite common, also since I am nearing a 150K!

 

Thanks for the advice, I will keep an eye on things!!

 

I wouldn't replace it unless you know for sure its gone.

 

The sending unit for your temp gauge is 20 bucks...a new cluster is $240, plus the cost of having it programmed.

[mattjulien]

i have noticed that gm trucks have overly sensitive guages. my ford's guages go up and stay put; and the gas guage doesnt flop around like a fish out of the water(like my chevy does).

[Nytemare]

i have noticed that gm trucks have overly sensitive guages. my ford's guages go up and stay put; and the gas guage doesnt flop around like a fish out of the water(like my chevy does).

Yeah thats true...ford gauges are crap

 

No you are right though...they are a little overly sensitive.