Chasing Idle/Temp issue after many parts replacements '93 4.0 ohv

[franklin2]

temp gauge is still dancing back and forth between O and L...wont stay put longer than 1 minute. gonna bypass the heater core and try that.

I hate factory gauges, especially the ones with no meaningful numbers. I have seen a lot of money and time wasted on what a erroneous factory gauge said.

Have you tried a infrared gun to check the temps? Are there any other signs that the engine has a cooling problem besides the gauge?

 

[RonD]

Have you tried Grounding the temp sender wire?
Should be a black/blue stripe wire

Gauge should go to HOT and stay steady, then start engine, see if it also stays steady, just testing if its an electrical issue

 

[Eddo Rogue]

I hate factory gauges, especially the ones with no meaningful numbers. I have seen a lot of money and time wasted on what a erroneous factory gauge said.

Have you tried a infrared gun to check the temps? Are there any other signs that the engine has a cooling problem besides the gauge?

I agree, but could be worse, some cars have just an idiot light, or nothing. I dont see any other signs of a cooling problem other than the gauge...Thats not a bad idea I do have an infrared thermo...I may install an auxillary temp gauge that has numbers as well

 

[Eddo Rogue]

Have you tried Grounding the temp sender wire?
Should be a black/blue stripe wire

Gauge should go to HOT and stay steady, then start engine, see if it also stays steady, just testing if its an electrical issue

I have not but thanks for the suggestion, it wouldn't hurt to try that so I probably will.

 

[Eddo Rogue]

On 4.0l OHV engine, just above thermostat housing on the intake manifold is a heater hose, thats the high point of engine cooling system, so as you refill via radiator air will flow out of that hose until engine/heads are full, no air

 

[Eddo Rogue]

On 4.0l OHV engine, just above thermostat housing on the intake manifold is a heater hose, thats the high point of engine cooling system, so as you refill via radiator air will flow out of that hose until engine/heads are full, no air

found it thanks

 

[Eddo Rogue]

Update: I reconnected the mysteriously detached egr vacuum lines, and bypassed the heater core and test drove. This seemed to help steady the temp a little but the gauge is still moving around. I left it running at first while pulling the hoses off the core and noticed the outlet line was flowing much less than the inlet...and looked a little cruddy. New heater core is on the way.

Besides that I think maybe the thermostat needs to "break in" because it seems the more I drive the less erratic my temp gauge gets. Bypassing the heater core did help, but not solve.

 

[RonD]

You mentioned that before, "break-in period", there is no break-in period for a thermostat, its just a cylinder with wax inside, wax heats up pushes valve open, cools down and closes valve
As an engine warms up and thermostat first starts to open the cold coolant in the radiator will come in and thermostat will close again
After about 10min of driving the system will reach an equilibrium, and temp will stabilize, going up a longer hill should increase temp a bit, or pulling a load temp should go up

Ranger temp gauge uses 210degF as 1/2 way, so after full warm up temp gauge should be just below 1/2, 190-195deg
Its quite normal for temp to go up to 225deg when under load, uphill or having a load, so just above 1/2

Found this 1 min video on how thermostat works:

 

[Eddo Rogue]

You mentioned that before, "break-in period", there is no break-in period for a thermostat, its just a cylinder with wax inside, wax heats up pushes valve open, cools down and closes valve
As an engine warms up and thermostat first starts to open the cold coolant in the radiator will come in and thermostat will close again
After about 10min of driving the system will reach an equilibrium, and temp will stabilize, going up a longer hill should increase temp a bit, or pulling a load temp should go up

Ranger temp gauge uses 210degF as 1/2 way, so after full warm up temp gauge should be just below 1/2, 190-195deg
Its quite normal for temp to go up to 225deg when under load, uphill or having a load, so just above 1/2

Found this 1 min video on how thermostat works:

Good info, awesome video.

 

[Eddo Rogue]

Another update: seems bypassing the heater core did the trick! The temp gauge now hovers right around the middle, and only varies slightly based on driving conditions. Waiting for new heater core now....

Idle is also back to normal since taping the throttle plate hole shut, so I will probably swap out the whole throttle body

 

[Eddo Rogue]

Also Thanks everyone for all the responses, and great info! This place and you guys are awesome!

 

[RonD]

Good stuff

 

[Eddo Rogue]

Hey everyone thanks again for all the replies. I did most of them lol. heres and update.

I did a day trip to a dry lake bed, about 300 miles round trip (including off road play driving). Here's how it went.

Idle was smooth and steady and not too high or low (about 1250 cold, 800ish idle, 700ish w/ ac on)
I still have tape over the throttle body hole though...My heater cycling affects idle, not sure if thats normal.

My one piece driveshaft swap really smoothed out the highway vibrations from before.

Temp gauge finally settled, and moved accordingly (slightly higher when going uphill w/ ac full blast).

Next is Efan swap, exhaust upgrade (making it myself), and addressing my throttle body.

Also gonna rewire the dome light and go LED. I ripped it out trying to get the bulbs pulled, because I couldn't get it to turn off with the door staying open, and my door jamb button holder rig didnt work. It never worked right anyways, the switch did weird things besides on/off...Plus I usually have a personal dome light (head lamp).

Not to hijack my own thread, but open to ideas on this dome light situation...my searching only turned up how to fix the more common issue of when it stays on permanently. mine turns off fine when the door is shut, its just erratic and wont shut off when the door is open, unaffected by the switch and knob

Also is it normal for the heater to affect my idle? it changes when I cycle the heater on/off...

 

[RonD]

Things seem to be looking better

When Defrost OR AC is selected the AC is on, thats about the only connection that should effect idle RPMs

So if Defrost is selected then "heater" on/off would effect idle RPMs

I think the blower motor(fan) is always on unless you turn it off, blower is an electrical load and if motor is drawing more amps than it should it could cause higher load on alternator which might effect RPMs

 

[Eddo Rogue]

Things seem to be looking better

When Defrost OR AC is selected the AC is on, thats about the only connection that should effect idle RPMs

So if Defrost is selected then "heater" on/off would effect idle RPMs

I think the blower motor(fan) is always on unless you turn it off, blower is an electrical load and if motor is drawing more amps than it should it could cause higher load on alternator which might effect RPMs

Looking better indeed! Yes, it is during defrost selection... I've always preferred the heat coming out of the defrost vents, keeps me and the windshield warm, instead of cooking my face and feet. Thanks RonD, I feel better now lol