What causes my temperature to rise 3/4 the way before fan turns on

Tiny
METHODMAN01
  • MEMBER
  • 1991 PLYMOUTH ACCLAIM
  • 2.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 81,000 MILES
Good morning, I hope this email finds you well, I am contacting you today in hopes that you can enlighten or give me your personal opinion. I own a 1994 Plymouth acclaim and I just bought a 1991 Plymouth acclaim that was sitting down without being driven for 13 years. I replaced all the fluids, but the car temperature keeps rising to 3/4 before the fan turns only when the vehicle is parked or stopped in traffic. I had a new radiator installed, new water pump, new radiator cap, new thermostat 160 degrees, had both temperature sensors installed new, a new radiator fan relay, and bled the system. The car runs great and it keeps cold when driving on highway, but my concern is that the temperature rises to 3/4 before the fan turns on and it cools the engine. Also the I had a mechanic check the head gasket and he said it was good as there was no white smoke coming out of the tail pipe, no water was on the oil, and it didn't have that many miles. The reason for my concern is because my 1994 Plymouth acclaim temperature never rises above 1/2. Do you happen to have any ideas on what the problem could be? The only possible thing left to do is to change the fan, but the fan does turn on with the AC on, and on its own just it waits till the temperature rises to 3/4 the way. Thanks in advanced for all your help.
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Thursday, April 9th, 2020 AT 8:29 AM

6 Replies

Tiny
ASEMASTER6371
  • EXPERT
Good morning,

A 160 thermostat is wrong. It needs a 195 thermostat for the engine to operate correctly with fuel mapping.

The temperature the fan kicks in is 208 degrees. That is preset within the ECM. It will turn off the fan at 175 degrees.

What brand coolant sensor did you use? That is the signal the ECM watches for turning on the fan.

I attached the description of the system and how it operates.

Roy
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Thursday, April 9th, 2020 AT 8:41 AM
Tiny
METHODMAN01
  • MEMBER
Well, I've previously installed a thermostat of 195 and a 180 and it ran hotter than it does now. Now the other Plymouth acclaim I have which is a 1994 has a 160 thermostat and it runs cold all the time with the fan turning on around 1/2 the temperature which does not allow the temperature to rise above 1/2. That's why I think something is wrong with this 1991 Plymouth acclaim. The brand for the thermostats I've used are Murray.
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Thursday, April 9th, 2020 AT 8:52 AM
Tiny
METHODMAN01
  • MEMBER
Now for the coolant temperatures I used MasterPro for Ignition 1 and Ignition 2 temperature switch sensors.
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Thursday, April 9th, 2020 AT 8:55 AM
Tiny
ASEMASTER6371
  • EXPERT
I would start by replacing the coolant sensors with the original brand as there sensitivity is different than the aftermarkets.

As far as the running hot with the thermostats, did your guy do a leak down test on the cylinders for the head gasket? Just checking the oil and looking for smoke is not a diagnostic. I did dozens of these heads from cracks that never showed smoke or coolant in the oil.

Roy
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Thursday, April 9th, 2020 AT 9:00 AM
Tiny
METHODMAN01
  • MEMBER
Yes, he did check each cylinder and we haven't lost any coolant. What is the original brand for these sensors?
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Thursday, April 9th, 2020 AT 12:04 PM
Tiny
ASEMASTER6371
  • EXPERT
Mopar. Parts stores will carry this brand but it is the top of the line and more expensive.

Roy
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Thursday, April 9th, 2020 AT 12:07 PM

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