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Old March 24th, 2020, 13:36
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streetpirate streetpirate is offline
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'87 always runs cold?

'87 always runs cold?




I bought a REM to diagnose this and I'm stumped. The dash gauge and the signal from the cts show that the coolant only ever gets to 160-170.

I put in a new thermostat and tested the old one and it opened near 195 where it was supposed to with no change in the running temp of the engine.

The radiator and water pump were recently replaced. I can't think this has anything to do with it but I never noticed cool running before that. The jeep rarely gets driven.

The REM shows the system running in closed loop from cold, never shows open loop during warm up. I thought the cts had to show at least 130 for the system to run in closed loop?

It failed DEQ showing it was running slightly rich, but due to virus DEQ is shut down for a while and I can't try again.




My thoughts were that it was stuck in open loop because the cts was showing cold, therefore running a little rich and failing emissions. It's odd that the dash sender and the cts both show running cold, that should be impossible if the thermostat is operating. I used my trusty Harbor Freight laser thermometer on the thermostat housing and upper rad hose (gets hot so I'm assuming the thermostat opens) and the surface temps are in the 140-160 range.




So the cts must be bad? But then why is it running rich while in closed loop? Why does it always show closed loop even when cold?

Im a little stumped and wanted to see if anybody has any ideas before I start throwing parts at it. Thanks.
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Old March 24th, 2020, 14:11
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lazyxj lazyxj is offline
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Re: '87 always runs cold?

Have you verified the temperature gauge's accuracy?
I used an infrared thermometer, aimed at the thermostat housing to take a reading, when the engine is hot.
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Old March 24th, 2020, 14:47
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Saudade Saudade is offline
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Re: '87 always runs cold?

Here's a link to testing the Renix sensors.

http://www.lunghd.com/Tech_Articles/...iagnostics.htm

The guage uses a different temp sensor located at the back of the head. Make sure the contacts are clean.

What radiator did you put into it?
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Old March 24th, 2020, 16:07
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Re: '87 always runs cold?

So I have a REM (renix engine monitor) that displays the sensor values that the computer sees, so both the cts and the gauge senders are reading around 165 fully warmed up. The radiator is a close-to-oem as I can get copper brass one, cost twice as much as the cheapo aluminum plastic parts store ones bought through a local radiator shop(apparently there is only one manufacturer in the US still making copper brass rads).



I have checked thermostat housing surface temps with an infared thermometer and still seeing 160-170, its a cheap one but always reads pretty accurate when I test it against a known temp.



water pump is a regular one from rockauto, only other thing Ive done recently is the oil pump.



I really want to assume it's the cts, but the fact the dash gauge reads the same from a different sensor makes me question that.

What about always running in closed loop? failing rich on emissions? according to the engine monitor the o2 is behaving normal.
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I'd have to say a hand sledge or an angle grinder is the most useful tool though. You can do anything from brutalize your fingers to breaking everything around the thing you're trying to hit/cut with them.
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Old March 25th, 2020, 05:38
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Re: '87 always runs cold?

It should run in open loop when cold.

I wouldn't doubt you got a faulty stat.
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Old March 25th, 2020, 14:42
BALTANAKT BALTANAKT is offline
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Re: '87 always runs cold?

I have had the same problem for two years. Tried 5-6 different t-stats. True Mopars are no longer available. Tried blocking off 3/4ths of the radiator. No change.

In my case, it warms up to middle on the indicator, t-stat opens, temp drops to 160, then raises up half a mark below middle. Sometimes lower depending on outdoor temps.

My theory is the water pump is pushing too much water.
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Old March 25th, 2020, 17:04
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Re: '87 always runs cold?

You might want to try adding a restrictor.

http://gojeep.willyshotrod.com/Howto...Restrictor.htm
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Old March 26th, 2020, 12:21
GravyDavey GravyDavey is offline
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Re: '87 always runs cold?

Interesting. I suspect that I might have the same problem. Haven't had any time to mess around with it, but I think I'll try the restrictor when I get the chance.
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Old March 27th, 2020, 11:40
BALTANAKT BALTANAKT is offline
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Re: '87 always runs cold?

Please post up the results if you try the restrictor.
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