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I bought a Ford with an unknown amount of miles. A 94 Ford ranger 2.3. runs better then you would expect, accept the coolant temperature. The first thing I did to fix the problem was flush the system, put fresh coolant back in and change the thermostat. I thought that would fix the problem because the old thermostat was stuck open. But the coolant temperature still was not reaching normal temperature. I then tested the temperature sensor but both the wire leads and the sensor were working fine.

A few days ago a hose from the engine block to the heater core blow off spilling coolant all over the road. Fortunately I was only going to couple miles down the road so I pressed on. Now despite my coolant leaking pretty bad my coolant temp rose to about normal operating temperature and that was after stopping at red light, getting on the interstate, stopping at another light.

I fixed that problem by plugging the lines that ran to the heater core. And the I flushed the system and added more coolant.

And then yesterday my serpentine belt broke driving down the road obviously stop turning the water pump and my engine coolant temp shut up.

After all of that I know every is working. I've run out of answers. And with a Texas summer coming up I don't want a fidgety engine cooling system.

  • Can you post a picture of the coolant needle when the engine has warmed up (say, after 30 minutes of driving)? – Hari Ganti Mar 23 '17 at 22:20
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How did you test your heat sensor? It's entirely possible that it's just reading wrongly. I'd replace it regardless because they're not expensive.

What's concerning to me is that it's possible that it's been reading below normal operating temp when in actuality it was scorching... that would then cause more problems.

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If the engine temperature does not reach operating range the obvious problem would be the thermostat stuck open or coolant to rich. You already replaced the thermostat but you may have put another bad one in. You can check it yourself by putting the thermostat in a pan of hot water to make sure it opens at the right temperature.

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    Unless it was a scrapyard part, it seems unlikely he'd have another bad thermostat... Also, the coolant ratio doesn't affect heat transfer to a significant extent on most vehicles, barring racing or heavy towing. If it did affect anything, though, it would imply he doesn't have enough coolant, since pure water provides better heat transfer to the environment. – Hari Ganti Mar 23 '17 at 22:22
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What about using one of these to follow the coolant path?

http://www.tmart.com/BENETECH-GM320-Infrared-Thermometer-50-320_p210715.html?cc=USD&fixed_price=us_us&gclid=CjwKEAjw_uvHBRDUkumF0tLFp3cSJACAIHMYfMQmHaQHv1kOed3CVVEjz1jjm-xhLzIurPtMGIVfhBoCydrw_wcB

These tools are super useful for all things heating and cooling related.

I've seen water pump issues cause unexpected cooling symptoms but it's not worth changing until you have some facts to work from.

I would also +1 to the idea of manually checking the new thermostat in hot water to make sure it opens and closes correctly.

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