Another overheating thread

[efjayatee]

You used a turkey probe....lol

Its a bit of work but you can cut the upper rad hose and put a temp sensor in between the hose to get a better measurement. But your scangauge2 should be reliable.

 

[mindcrash]

You used a turkey probe....lol

Its a bit of work but you can cut the upper rad hose and put a temp sensor in between the hose to get a better measurement. But your scangauge2 should be reliable.

Yeah I know, not the most precise instrument, but I’m pulling my hair out here lol. I trust the scangauge, it’s the sensor that I question because of all the work that’s been done otherwise to refurbish the cooling system.

If I were to get an actual thermocouple would testing that pipe be a good way to confirm?

 

[efjayatee]

You would want the temp sensor to be immersed in the coolant. Getting the temp of the hose or metal pipe isn't a great way.

You could also replace the ECT sensor that is located on the side of the block next to the knock sensors.

When i did the HG, I replaced the 2 knock sensors, ECT sensor, fusible link, EFI, TPS......pretty much sll the sensors, including the fan clutch from Redline & 15k viscosity oil.

 

[TheBussman]

I've seen a sensor be off by about that much before, made me think it was overheating when it wasn't. a thermometer touching a clean aluminum cyl head or coolant outlet should be with 10 degrees, i use a thermal camera now.

 

[Mark W]

A while back I brokered a deal on an FJ60 for the daughter of one of our Mud members here when she came to Alaska for the summer right after she graduated college. It is actually a pretty long and interesting story but I'll stick to the sorta kinda relevant part for now.

A couple of years after she purchased it here in Alaska she drove it down the Alaska Highway. Her dad had designated me her "Alaska Dad" at the time, so when I got a call not *too* late the first night I answered immediately. She had only made it to Tok (just over 350 miles)that day and was stopped (stuck?) there with an overheat problem.

I headed out right away with tools, prime suspect parts (Thermostat, fan assembly, coolant and the like), and a sleeping bag. I know the road and have driven it lots, so I made good time and rolled in about 6 hours later and tossed my bag on the picnic table at the campsite she had found (right in town even) and caught a couple hours of shut eye.

She's a smart girl (graduated college at ... 22 IIRC... with TWO degrees and is a dentist now) and she is not a timid girl (last person to summit Denali for the season a couple of years ago now) so I knew from the get go I could trust her (admittedly amateur) evaluation of the situation, but of course I was gonna check it all out anyway.

Checked the coolant levels, checked the fan clutch, checked the thermostat... all good... test drove it and watched the temp gauge climb. Seemingly pretty quickly. I had been using the hand held gauge all along, but we really had not run it long enough before the test drive to even really warm it up. We jumped out and started checking all the interesting points (back of head, middle of head, front of head upper and lower rad hoses, rad itself, thermostat housing, water pump, bypass hose, heater hoses... pretty much everywhere.

(Now this is a 2F we are talking about now, but the lesson applies...)

Every point I checked was nominal and perfectly appropriate for the conditions the rig was being operated under.

IT WAS NOT OVERHEATING, regardless of what the gauge had been and WAS now telling her.

I just realized as I am typing this that I never found out if it was the sending unit or the gauge that was lying to her. Since this happened her father has swapped a 2H into the rig for her and so far it has not made it back up. I *think* it was the sending unit... not sure right at the moment.

But, I had not brought a sending unit or a gauge with me. No matter how many spare parts you carry it is always gonna be the one you left behind that you need.
I did not make a 700+ mile round trip to get the two pieces.

We stopped in the NAPA. If you are coming to or leaving Alaska by road you WILL go through Tok. It may be a small place... but they have a NAPA!

We picked up a handheld infrared temp sensor (the only one in stock/in town) so that she did not have to take mine with her. She headed off down the highway for Illinois with her new tool in hand. For the first day... first couple of days.. she stopped a lot to confirm that the gauge was lying and that everything was in fact copacetic. As time passed she got more comfortable and did not check it nearly as much. And the daily check in phone call switched to the other end of the trip.



So... another overly long story from Mark.

My only point is... if the engine is not showing other overheating symptoms besides what the gauge(s) are telling you... don't rule out that they may be lying. Sending units can fail too, not just the actual dash gauge.

Pick up a handheld infrared sensor. Probably find one in any parts store or big box hardware store for under $30. It is a very handy tool.


Mark...

 

[landtank]

Sorry if this has been mentioned but if you wheel in the dirt you should power wash your radiator regularly.

 

[mindcrash]

Sorry if this has been mentioned but if you wheel in the dirt you should power wash your radiator regularly.

Radiator is brand new, no dirt to speak of yet. But thank you!

 

[Kernal]

"---could the water temp sensor be bad?"

IME, yes. Replaced the ECU/EFI temp sensor (Sensor, Water Temperature for EFI 89422-35010) in my stock 97 model and the scan tool temp reading went from 180'F to 190'F (flat road, no load). So in that situation the original sensor was reading low and the actual temp was 10'F higher.

 

[alia176]

Ok, i'll do couple of WAGs and see what works.

So, you're radiator is brand new and you now have 30k CST fan clutch fluid (it's a band aid, not needed in DEN) and you're still pegging the heatOmeter.

You should have serious air flow, and you have a new head gasket. The HG project is an interesting variable to me. Since the work was done by a shop, I wonder if they skipped a step. Since you aren't losing coolant, at least your HG isn't leaking again.

I trust your OBD-II water temp reading, but if your A/C is cutting off while this is happening, then your Scangauge is telling the truth. I think a/c cuts of at 216 or 220 deg but don't quote me on that.

Using an IR thermometer, please pull over when this overheating is happening and tell us the radiator inlet and outlet hose temp. If you can shine the IR temp gun on the metal pipe rather than the rubber hose, that'd be mobetta. There needs to be a large amount of delta between the two hoses so that we know the radiator is pulling the heat out of the engine. I want to know that delta temp.

I wonder if you're getting air flow through the A/C condenser and then through your radiator? By any chance is your a/c condenser full of dirt/debris and the fins are clogged? I bought one of these cleaning wands for cleaning the radiator and the a/c condenser.

As someone might have pointed out previously, is the "jiggle" hole up top, as in 12 o'clock on the thermostat and is it installed correctly? Since you didn't do the work, mistake could've been made easily by the tech not paying attention.

Anyway, let us know what you find out.

 

[mindcrash]

I haven't gotten to the thermostat yet as I'm waiting on a new one to arrive, for the cost I thought I would just replace it. I also ordered a new ECU coolant sensor. I will also get the radiator cleaning wand linked previously because it can't hurt to spray the A/C condenser as I'm sure it's original as well.

In the meantime I got ahold of an infrared camera and did some recording today. The scangauge was reporting 184 when these measurements were taken.

Upper radiator inlet - rubber hose: 170.1
Upper radiator inlet - metal pipe: 171.3
Lower radiator outlet - rubber hose: 148.1
Lower radiator outlet - thermostat housing: 149.2
Radiator (taken at top of radiator itself): 172.4

So is ~13 degree difference between the inlet pipes and the exterior of the radiator an acceptable delta from the temperature the sensor is reporting?

 

[Marvelicious]

"---could the water temp sensor be bad?"

IME, yes. Replaced the ECU/EFI temp sensor (Sensor, Water Temperature for EFI 89422-35010) in my stock 97 model and the scan tool temp reading went from 180'F to 190'F (flat road, no load). So in that situation the original sensor was reading low and the actual temp was 10'F higher.

Just out of curiosity, how did you determine which temp was actually accurate, or did you assume that the new sensor is correct?

 

[Mark W]

Just out of curiosity, how did you determine which temp was actually accurate, or did you assume that the new sensor is correct?

I haven't gotten to the thermostat yet as I'm waiting on a new one to arrive, for the cost I thought I would just replace it. I also ordered a new ECU coolant sensor. I will also get the radiator cleaning wand linked previously because it can't hurt to spray the A/C condenser as I'm sure it's original as well.

In the meantime I got ahold of an infrared camera and did some recording today. The scangauge was reporting 184 when these measurements were taken.

Upper radiator inlet - rubber hose: 170.1
Upper radiator inlet - metal pipe: 171.3
Lower radiator outlet - rubber hose: 148.1
Lower radiator outlet - thermostat housing: 149.2
Radiator (taken at top of radiator itself): 172.4

So is ~13 degree difference between the inlet pipes and the exterior of the radiator an acceptable delta from the temperature the sensor is reporting?

That seems about right... normal, nominal to me. The ECU temp sensor is in the middle of the head (more or less) on the left hand side. The back of the head is generally the hottest area of the engine. That is why the heater hose feeds from there. I checked air temp from the heater after a vigorous core cleaning once and had 210+ degree air coming out I a m sure the coolant was warmer that that.... while the engine was running with no real load, just "on the thermostat". The thermostat maintains a constant "appropriate" temperature but that temp IS NOT universal all the way across every point in the engine.
Coolant gets pushed into the block from the pump and *most* of it flows toward the back of the block and up into the head before coming forward, but not all of it. Various passages along the way allow some to move into the head without making the entire trip. So... the front of the engine is cooler than the rear and the thermostat, the outlet and the coolant reaching the radiator is gonna be cooler than the back... AND the middle of the head.

That is the reasoning behind checking various points on the engine when trying to ascertain what is going on when you have cooling issues. After you have looked at a few engines this way, you pick up a feel for what to expect to see at the different locations.


Mark...

 

[CrabCake]

On my 94, I have the ZF scan tool that plugs into my OBD1 port and reads the temp from the OEM sensor that feeds the ECU plus the Koso gauge that I plumbed into the upper radiator pipe (tapped in the aluminum outlet right next to the block). I can see 8-10 degree differences in the 2...that said, the OEM sensor seems to only read in +/- 4 degree increments whereas the Koso is by degree (and always cooler than the block temp).

Highest temp that I've ever had was 212-214 on the OEM sensor under load on hard hills, but usually hangs around 208 which still makes me twitchy! My setup was recently refreshed within the last couple of years including the landtank blue hub/modified version that I just bought as a finished unit from him, whooshes a lot more than the OEM at any temp, but really didn't make much difference in overall temp readings.

 

[ceylonfj40nut]

Does your AC cut off when engine cuts off? Are your belts tight? Did you burp your engine properly? Did you do a test to see if you have a headgasket issue using radiator fluid test?

 

[mindcrash]

Does your AC cut off when engine cuts off? Are your belts tight? Did you burp your engine properly? Did you do a test to see if you have a headgasket issue using radiator fluid test?

Yes, yes, yes, no....but I did have the oil tested by Blackstone after my oil change a couple of months ago and no problems noted.

 

[Broski]

If you’re AC is cutting out that would indicate you are overheating

 

[MissahPapaJ]

If you’re AC is cutting out that would indicate you are overheating

Correct me if I’m wrong but if the sensor is bad or at least off in resistance spec it’s gonna tell the ECU to cut A/C cause it’s set to certain parameters. I think I would test the ECU sensor to make sure it’s actually seeing correct resistance at the particular temps. The gauge sensor is just relaying information to the cab but the ECU sensor is keeping everything else in harmony on the engine side. And that’s the sensor that a scan gauge gets info from.

 

[Broski]

Correct me if I’m wrong but if the sensor is bad or at least off in resistance spec it’s gonna tell the ECU to cut A/C cause it’s set to certain parameters. I think I would test the ECU sensor to make sure it’s actually seeing correct resistance at the particular temps. The gauge sensor is just relaying information to the cab but the ECU sensor is keeping everything else in harmony on the engine side. And that’s the sensor that a scan gauge gets info from.

Most likely true and why I run a market gauge

 

[Dirtyfingers]

Hey there, I am new here, made an account for this thread, as well as for the fact that i just bought a 95' LC myself, when you did your rebuild, did you make sure to remove all FME? (Foreign material exclusion, for those that don't know). this would require removing everything you've done to rebuild. start with the water pump and make sure it doesn't have any FME clogging flow.

I am only suggesting this out of experience. I had a team of sailors that we were reinstalling the jacket water cooling on a main engine on the ship. One section of it, we did not remove the FME and stopped cooling flow during testing.

 

[Kernal]

"---how did you determine which temp was actually accurate (old versus replacement temp sensor)---"

IIRC I checked the resistance of both the original 30 year old EFI/ECT temp sensor and a new NGK sensor. The old sensor read somewhat higher (ohms) compared to the new sensor (~same temp) so not a hard failure but a potential drift in resistance. I did not however test the old sensor at multiple temps so IDK if it was better or worse at those other temps. Either way, we know higher resistance than it should be in that sensor causes the ECU to "think" (see/read) that the engine is cold(er) than it actually is.

I was not however chasing the same situation as the topic of this thread, I was tracking down the cause of a high idle (950-1100) along with intermittent bucking while driving at a steady ~ 45mph. After hooking up a scan tool to the OBDII port I watched the TPS signal drop/change abruptly at the same time as the (engine) bucking. So I replaced both the TPS and the EFI/ECT temp sensor at the same time, problems fixed, no bucking, more stable idle back to the correct rpms, acceleration that "felt" better (smoother/stronger), and the higher temp OBD II readings under the same conditions.

FWIW