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Discussion Starter #1
Hello Everyone!

I recently bought a 1989 Chevy S10 Tahoe and I am having some overheating problems.The trucks runs nice and stays at a good temperature for a good 5 minutes, but then it starts overheating. I already replaced the water pump, the thermostat, and the 1 probe lower block temperature sensor. I am also currently flushing the system with water and Prestone flush.

When I turn the hot air on, hot air comes into the vehicle. Does that exclude a bad heater core?

I have a digital cluster that it is also being weird. Some digits of the speedometer don't work and the tachometer is working and not working intermittently. Is it possible that the cluster is bad or has bad contacts causing the gauge to show overheating?

Fan clutch is though to spin when the engine is cold so I thought it was in good shape. When it gets warmer it spins a little easier. I don't know if that's normal.

I also didn't find any milky coolant.

Please, help me if you have any idea of what it could be. I am struggling to find an explanation. Thank you!!
 

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All Show & No Go
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Since you have replaced the pump and the T stat. I would start looking at your radiator. There could be a lot of rust and calcium deposits. If someone ran tap water for an extended amount of time, you probably have minerals blocking the radiator channels. A flush will not get rid of minerals that have built up.

I bought a decent all aluminum radiator from Rock Auto for $129.89 about four weeks ago. LILAND GLOBAL radiator part number 705AA at rockauto . com. No complaints so far.

Also. My Temp gauge will stick from time to time. I give it a smack with my hand and its starts to behave.
 

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Discussion Starter #3
I forgot to mention the radiator is somewhat new. The previous owner changed it just before selling the truck probably due to the overheating problem.

One thing that is weird is it will run fine most of the time, then it overheats fast(20 seconds) and sometimes will cool down just as fast.

I will investigate the cluster tonight or tomorrow. I will take it apart and see if there is something shorting. I will also check the wiring from the sensor.
 

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Mew Nember
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Run a $20 coolant temp gauge. Can even zip tie it under the hood (mechanical but keep it away from the header, fan, steering, etc.) or run it into the cabin. Go drive it. Let the engine get to temp, but go off the new gauge. My 2.8L hangs out around 190-195 when it had the mechanical fan and now electric fan.


If the temps stay in range but the dash temp is going wonky, it's electrical. I'm running into a minor electrical issue on mine, that's seemingly related to the 14 gauge charge wire off the alternator running back in the loom (dunno wtf they were thinking running a tiny wire like that even on low amperage, and it doesn't even directly go to the battery). In my case, I noticed the passenger headlight was dim and the heater motor is intermittent, so I'll need to look at the wiring.


Dunno what '89 was like compared to my '82, but if it is electrical, it might have fooled the PO into thinking it had overheating issues and might be easy for you to fix.
 

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Yes that is a good idea to test the electrical. I actually drove the truck for 15-20 minutes with a diagnostic tool from O'Reilly and was hoping for it to overheat to check the temp, but didn't happen so I thought the truck was fixed. It was actually just after installing new parts so I was like ok good!

I will try again now. This time I will probably run a wire from the engine into the vehicle and hook up an ohmmeter to it. I found tables so I can cross reference temp with resistance.
 

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Mew Nember
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Keep in mind, the sensor could be wonky.



If you suspect electrical, can put your phone on record (self mode/ front camera works if it has one) or just set it up w/o recording, and point front camera at dash and mount it on the column or something. With engine running, watch it through the windshield and try moving wires in the main loom. See if it reacts on-screen.



On my '82, I moved the wiring loom directly after the alt charge wire connection behind the alt, and the dim headlight corrected. GL.
 

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Discussion Starter #7
Got some news!

I hooked up the ohmmeter to the sensor and went for a big ride (I was doing some hard accelerations also). The temperature on the ohmmeter makes sense and I was around 200 F. The funny thing is that I was using the regular cluster to drive but I was stopping tho check the ohmmeter. Regular cluster stayed at 200 and didn't move one bit.

Now I hope that I only have to figure out one thing:

If the cable ( I moved it a bit is the problem)
If I had a huge air bubble (or deposits)in the cooling system. I am also suspecting this since the the coolant tank went lower and the radiator was topped just good( it was low in the past few days and I topped it)
 
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