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Order of operations: coolant temp issues


spmls

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I've got a new to me '98 3.0L with 150k on it. Temperature gauge on the cluster has never really crossed the low end of the "normal operating range", even when climbing steep highways in California (not that cold outside). I've checked the sender wire and gauge (full deflections when disconnected and then grounded to engine block), replaced the sender with a new Motorcraft, and the situation has not changed.

I plugged in the OBD and drove around for a bit, and the temperature there never seemed to get above 60°. Got back, engine certainly felt warm. Upper radiator hose was much warmer than the lower one.

Another symptom: Cabin air doesn't every blow in cool outside air. Once the engine is on, if the fans are on, even full cold (without a/c on), there's still hot air coming in.

So should I start with replacing the thermostat (is it stuck open)? Or with a new coolant temp sensor, or do I have bigger issues?

Thanks.
 


Rock Auto 5% Discount Code: 7FA902352B4C01: April 5th, 2021

Uncle Gump

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I think I would start with an ECT sensor... but I would use a mechanics thermometer to see what temp the coolant actually is.

As for the cabin air blowing hot in the cold position... that sure sounds like a blend door issue. It's fairly common on these trucks and I know mine just went out. It's stuck on HOT but until it get warmer outside (currently -2 degrees) I'm OK with it being stuck on HOT.
 

Orca

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Welcome to the forums!
I plugged in the OBD and drove around for a bit, and the temperature there never seemed to get above 60°. Got back, engine certainly felt warm.
Something here doesn't make sense to me. Are you reporting ECT (Engine Coolant Temperature) from the scantool as 60 degrees Fahrenheit?!? Or is that Celsius (the default units as it's reported by the vehicle)?

When the engine is "cold" from not having been run for many hours, does the reported scantool ECT match the ambient outdoor air temperature (within reason)? When the engine is still cold, you might also want to check the "Intake Air Temperature" (IAT, also reported by default in Celsius) report from the scantool against the ambient air temperature, as a further "sanity check".
So should I start with replacing the thermostat (is it stuck open)?
Determining if the thermostat is stuck open should be relatively easy. In fact, I just made a post about this in another thread, in case that helps.

EDIT: for clarity of meaning
 
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Dirtman

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I'm with that whale guy, you cant have the engine temp be 60F AND have hot air blowing from the heater... the air from the heater can't be hotter than the engine lol.
 

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Thanks Orca. Yes 60° Celcius! If I have a 195° F (91° C) thermostat installed, this is still 30° C too low. Looking at the ECT graph, the temps gradually rise and then stabilize around 60° C, there doesn't ever appear to be a drop in temp that would indicate the thermostat going from closed to open. And as you suggested in the other thread, I checked the return line and it gradually warms.

Have a new 195F motorad thermostat and gasket maker on hand so I'll give that a go this weekend. Don't know if that would also fix my hot cabin air issue, but we'll see. May have to replace the blend door as Uncle Gump said.
 

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Yes, the two are unrelated

Someone may have put in a 160deg or 180degF T-stat, or yes it could be leaking a bit
60degC is 140degF which is of course low after full warm up, 185degF(85degC) would be expected with 195degF t-stat, as shown on computer(ETC sensor data)
Ford Temp gauge has 200-205degF as center line, so just below 1/2 would be expected after full warm up from Temp Sender on engine

Blend door was a common issue on 1995 and up Rangers, and Fords in general
Adjust the TEMP knob and feel if the temp of air changes, if not Blend door is not moving
The blend door is between Fan and heater core(in essence), it routes air from the fan either thru the heater core or around the heater core, the TEMP knob controls the electric Actuator that moves the blend door to route some or all of the air thru or around the heater core
 

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Thanks Orca. Yes 60° Celcius!
Ah, good... that makes more sense! Thanks for clarifying. I feared we might not hear from you again. ;)

Good plan to change the thermostat. You've now got 2 good bits of evidence in favor of it being stuck open, so I think your plan is wise, FWIW.

Good luck and please keep us posted on your results!
 

Dirtman

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Get the band aids ready, you will be skinning your knuckles getting the blend door motor out...
 

Shadowrider6661

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You may have already checked this but, as far as the excess interior heat, is the vacuum ball that controls the heater working right ? I had the same problem awhile back and that fixed the excess heat. I'm just throwing ideas out there, you never know what might help.
 

Dirtman

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You may have already checked this but, as far as the excess interior heat, is the vacuum ball that controls the heater working right ? I had the same problem awhile back and that fixed the excess heat. I'm just throwing ideas out there, you never know what might help.
On 95+ trucks the vacuum ball only powers the vent actuators (Forward, floor, defrost). The actual temperature is controlled by the electric blend door motor. If there was an issue with vacuum the vents would simply get stuck blowing from the defroster, but you would still be able to adjust the temp from cold to hot.
 

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My apologies, my blend door and temperature control operates by vacuum. I may have an unusual setup, who knows !
 

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Heater core shut off in engine bay is vacuum controlled but its not a temp control its either an open or closed valve
Its closed(vacuum present) when OFF or MAX AC is selected in the Cab, and open(no vacuum) in all other settings

Ranger Blend door was cable operated thru 1994, used Sliders on the climate control to move the temp cable
In 1995 Ford switched to electric actuator for blend door, and a Temp Knob to control that actuator

The vents, i.e. defrost, panel, floor, are vacuum operated in all years BUT up to 1994 the vacuum control was cable operated, via slider on climate control
From 1995 and up a knob selected vacuum routing to vent "motors"
 

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Ok, pulled the old thermostat this evening and installed a new one. Waiting overnight to refill and test it out.

Turns out someone put in a 71° C/160° F thermostat (left one, picture below) at some point. I now have a 90° C/195° F in there, so we'll see what happens.

The old one didn't appear to be stuck open when I popped off the housing, and it doesn't seem to hang up when I press on it now 🤷

55945
 

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A JIGGLY HOLE!

Does the new 195 t stat have a jiggly hole? (The lil thing on the side that lets air out)
 

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Glad to hear that your problem seems to be solved now! Of course, some road-test results would be even more interesting (hint, hint :)).
The old one didn't appear to be stuck open when I popped off the housing, and it doesn't seem to hang up when I press on it now🤷
It's been a few years since I last replaced a stuck-open thermostat, but I don't recall any signs that the old thermostat had been stuck open upon visual inspection after I'd replaced it. But the replacement solved the problem ever since then. And the graph of ECT with the new thermostat shows a drop when it opens, whereas the old thermostat didn't.

Thanks for the update!
 


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