​​​​​​so.. You have two sensors, one feeds the dash the other feeds the emissions computer.. If the dash sender isn't getting a good ground it's going to show the wrong temp on the gauge.. If the emissions computer isn't getting the right temperature it's not going to do its thing correctly..

I said thermometer, as in the one you say reads 197 with the 190 thermostat..

Your head and engine are going to have spots that are hotter than others.. Give locations others can check against and accurate numbers..

Well yeah if the heater core is feeding hot water straight back to the pump it'll be a little hotter than if it wasn't.

 

The heater core should have no affect (ok, an insignificant amount) on how well the rest of the cooling system performs. The heater core is only there for interior heat and is not needed for engine cooling.

However, if your engine does overheat, the heater core is just a little radiator in your dash that you can use to help bring the coolant temperatures down.

I am still thinking you are not overheating, but I am not there to read the temperatures myself.

 

Do a reverse flush on the cooling system. It could possibly have some built up gunk in the engine/hard pipe.

When I tore mine apart last year, one of the cylinder head water jackets was at least half way clogged with RTV boogers. Previous owner had way overdone it on the water pump that does not need RTV.

 

An update -- the truck is finally running at an acceptable temperature. The gauge is fine.

The solution consisted of flushing the engine and the mostly clogged heater core. The engine didn't have anything nasty in it that came out like the heater but I'm sure there was some residual crap in there. I've been driving it for the last two days and the temp gauge is where it is supposed to be - 1/3 of the way up.

 

Call me skeptical, but I find it hard to believe that no flushing was done during any of these myriad repairs/replacements and now,
magicly, that's all it took to correct your problem.

 

But.. middle is "correct". Now it's running to cool.

 

Not with these trucks. Normal is anywhere between 1/3 to 1/2 up the gauge, depending on the particular gauge and how the gauge feels about the shirt you are wearing.

 

Yup my 92 runs at 1/3 on the gauge with a Tama 88C thermostat, and with the Toyota Kuzeh 88C thermostat I installed the other week. I can say though the Toyota Kuzeh makes the gauge more responsive especially if I get on it through the gears, but then it's not half way but close. Then it comes right back down to 1/3 with normal driving.

 

I'm not a magician and I didn't hire one to work on this issue. A hose was not hooked up to the heater core until Friday morning and the engine was not previous flushed with high pressure water.

That is all that was done to get the temp running - according to the stock gauge - normal. I wouldn't hold anything back with what solved my issue because that wouldn't be helpful for anyone that may run into the same problem.

 

When I bought my 89 back in 1989 - the gauge only ever got to 1/3 when everything was "normal". Even the 3.0 I had purchased new ran in the same range.

 

thank you for sharing your fix...

 

Doh! I see this got answered a bit ago. Never mind.

Please forgive me if this seems too simple....I've done this once in my shade tree mechanic career....verify the thermostat's flow direction. Getting that backwards will block water flow. Good luck on this one, you are getting a very thorough education!