When I first got it a couple of months ago, I had noticed that once it warmed up, my LT1 never seemed to run any lower than 210 and sometimes as high as 240 on the analog display. The dealer's service manager told me that was within spec for these engines. I was all set to pull and clean the radiator, coolant flush, etc when I read another post mentioning the digital coolant temp display which I had forgotten all about. I checked it and sure enough, it was showing a good 25-30 degrees cooler than the analog in traffic and 5 degrees cooler on the highway. So I said OK, and figured the analog guage was just a little wacky.

Then today I read the "Cooling System problems. '96 LT4 Help!" post ( http://forums.corvetteforum.com/zerothread?id=649009 ) where FoolCrzy
was getting 210 or so on his digital and 260 on his heads after a water hose change and was advised that there might be air in the system.

I recalled from a previous cooling post ( http://forums.corvetteforum.com/zerothread?id=640186 ) that "The digital gauge and the analog gauge have their own sensors. The digital sensor is at the front of the motor by the water pump. The analog sensor is on the left side cylinder head between #1 and #3 pistons."

So does that mean it IS possible for the higher analog temp because there's air in the heads and NOT because the guage or sender unit is messed up? Does the previously mentioned fact that the temp difference between my analog and digitl guages while at highway speeds narrows considerably indicate anything? I know the T-stat had been replaced prior to me purchasing the car. FoolCrzy speculated in his original post that his water pump might be partly responsible for this as well as air bubbles. Would less than optimal water pump performance factor have anything to do with this?

Of course, this all might be moot as the car is currently in the shop for a water pump/opti replacement which means if the problem is either the water pump or air in the block, that should be taken care of by the repair. Would that mean if the temp readings on the two guages come back into line then both guages were right, after all?
Thanks


[Modified by tobijohn, 2:31 PM 9/12/2003]

 

:D

The analog gauges do not represent the reading correctly. They are not linear. I don't know if you still have the sticker on your gauges from GM stating that the analog gauges are not an accurate representation of the correct reading (or something to that effect). It took me a while to realize that when the temp gauge was at 3/4 of the way to 260, the car was really running 220. I thought it was around 240. I have been running 200-210 on the Turnpike at 75mph the past couple of weeks. In town, I have been as high as 235 when sitting in heavy stopped traffic. But, once I start to move, the temps drop back down to 220 or lower quickly.
:cheers:

 

It's a little sad, but the analog gauges on the dash are only for a reference and not to be used for an accurate reading.

When the car was new, there was a sticker on the Speedo saying so.

I would just rely on the digital numbers, because that's what the ECM sees.

 

Whitvette wrote:
"The analog gauges do not represent the reading correctly. They are not linear. I don't know if you still have the sticker on your gauges from GM stating that the analog gauges are not an accurate representation of the correct reading (or something to that effect). It took me a while to realize that when the temp gauge was at 3/4 of the way to 260, the car was really running 220. I thought it was around 240"

I did the math and figure that it's about 25 points per gradient on the analog. That would mean the line above 260 was about 235 and the next one up is 210. When the analog guage is on the line above 260, the digital reads 205. When the analog is on the second line up (210?) while on the highway, the digital reads 200. Screwy.... :crazy:

 

:crazy: You know it!! :crazy:

 

Rather than just tell you that the analog gauge is screwed up and inaccurate I'm going to attempt to answer one of your question. No matter how inaccurate the analog gauge may be you brought up an interesting point, the differential in temperature is greater when you are moving vs when you are sitting still.

My car actually does not have this problem, because of my electric water pump. The normal mechanically driven water pump flows more water when the engine turns. It also runs off the cam so it's running at half crankshaft speed, meaning that if you're idling at 750 RPM's your water pump is only going to be turning 325 RPM's. Since the volume of water pumped at idle changes you can easily account for the difference.

When you are at idle the water in the head and block is moving slower. Any given "part" of the water has more time to gain heat, therefore it will be hotter. When it gets into the radiator the same is true. Any given part of the water has more time to cool off and the cooler it will be by the time it gets back to your sensor.

With an electric water pump that runs at a constant speed all the time you won't see this.

 

Great....guess I know what I am going to have to do when this pump starts to go bad....go electric. :crazy: :smash:
:cheers: