I know this is said in lots of places in other threads...

But, do not trust that OEM temperature gauge when considering if your engine is 'running too hot'.

Summary:

I replace bad temp gauge (no reading at all) with another used gauge (worked better, see below).
Replaced gauge sender
Swapped clutch fan for electric fans with a thermo switch set to go on at 185 (the summit racing wiring kit)
Added a 'block temp switch' set to tun on at 200
Had OEM 195 thermostat installed.

The dash gauge consistently read 250-ish when engine is fully warmed.
Fan switch NEVER clicked on.
Block Thermo switch NEVER clicked on.
I read the gauge as the engine was 'running hot', so I replaced the 195 thermostat with a 180.
Dash gauge indeed read about 15 degrees cooler, but...
The ECM started throwing codes complaining about engine running too cool.

I thought maybe it was hotter near the gauge sender (left lower side of engine block), than at the thermostat housing (where fan switch is installed). So I swapped them. Nope, dash gauge still read 250ish with the sender at the thermostat housing.

Finally broke out the infrared temp gun and verified temperature at the side of block is the same at the thermostat housing. Both in the sweet spot of 170-190 degrees).

So, I have three data points saying temperature is < 200 degrees, with a gauge that reads 250 degrees. Which one is most likely WRONG???

The gauge of course...

Moral of the story... double check your temperature readings with something reliable before deciding your engine is 'running hot'.

 

A properly working factory temp gauge works fine but I always recommend this to make sure:

https://smile.amazon.com/Mr-Gasket-2...perature+gauge

 

ECM live data. There's really no excuse for not having an ALDL cable and free software to handle this aspect of vehicle maintenance. Manifestly you are doing your own work and you have a computer or some way to post on thirdgen.org so.....

Part of being a mechanic in the age of computers is working WITH the computer. Also infrared temp guns are really cheap, and even thermal imaging cameras have come way down in price. There are soooo many ways to troubleshoot that doing it with Visa by throwing parts at it is completely unforgivable.

Shame.

GD

 

Since I think your post is a "don't forget the basics" reminder, I'll add to it because way too many people don't understand. It always cracks me up to see someone chase an "overheat" problem with a lower temperature thermostat. A thermostat does not control the max coolant operating temp, it controls the minimum. People need to stop trying to fix overheating with a lower temp thermostat.

 

Cool. Never seen those before. Brilliant idea.

 

Yeah, I was looking at those cables online yesterday. In my case the CCC carb ECM doesn't give out much information. Not much more than could be measured through other means. Maybe one of these days I will shell out $60 for the cable.

 

Yes, the thermosat temperature is the 'minimum temperature where coolant will flow' (unless you have drilled holes, which should not be necessary unless you have other problems).

The only time a thermostat replacement might fix an overheating problem, is when it is defective and 'stuck' close. Which is what I originally suspected in my case (it was not).

 

I agree with you in terms of min temp. But on the other hand, I've seen some pretty rusty thermostats come out of cars. And who knows if they're opening all the way or just halfway? Stant thermostats are something like $4, $6, or $9 depending on economy/regular/premium choice. For that little amount of money, the best thermostat they offer is worth it to me.

 

I see no problem with checking or replacing a thermostat, but too many people want to jump to a lower temp as if that will solve their problem. At best it might mask the real issue.

 

Something like this would help aid in determining if a thermostat is opening and closing properly and you can monitor the coolant. I'm thinking of getting one of these:

http://www.jegs.com/i/Cool-View/067/CV0180CH/10002/-1

 

Looks like a leak in the making to me ....

 

Wow. Totally getting one of those for my truck. Bling!

GD

 

My factory temp gauge is off, got better after I replaced the sender but is always at least 20F too high. Before I replaced the sender it would redline when my fan came on at 211 and my aftermarket gauge and heat gun read 210.

 

My 89 has been spot on. One thing to note tho is the half way tick mark is not half way in temp. First mark is 100 then other marked 220. Half way tick usually reads near 190-195 from what i have seen

 

That is a good point, it is not a linear gauge