Weird Overheating Issue

[Antznyopantz]

Tl;dr

Dummy gauge topped out at high. Scangauge at 164.

Setup:

'99 with 197k miles.

Had it out of service for a few years working on extensive body repairs and paint. It was my first paint job. Awesome. Came out sweet.

Reassembled the vehicle including the interior, dash, gauge cluster etc.

Gave it a tune up. Replaced the radiator out of caution.

On its maiden voyage to work car was overheating - temp gauge climbed in Toyota fashion, topping out quick - minutes from home. Did not seem to show any difference between stop/idle and going down a freeway on a cool day (low 70's maybe?) - or with heater on.

Suspected the thermostat so replaced that and the water pump this past weekend. It was all only 20k miles old- but it had been several years. Whatever. Had the parts on hand. Water pump looked great. Thermostat had several white calcification pebbles from the coolant on it so I thought perhaps that was the problem.

Buttoned everything up. Cranked it up. Sounded great.

Still overheating.

Here's where is gets weird:

Hooked my scangauge II up to the car and the water temps were at 164.

OK - so is the engine overheating? If not - why is the dummy gauge telling me it is? Is the sensor bad?

Will likely do a leakdown test tomorrow - but I don't think it's a HG issue.

Any ideas helpful. Thank you guys!

 

[thegipper]

If you weren't having any symptoms of overheating other than the needle gauge saying so, I'd say your coolant temp sensor may have gone bad or you have air in the system.

 

[Wedgy]

You could try a temp gun on the radiator fins and see what it reads, hot water comes in the top. Won't be exact but you might get an idea of what temps you are running. I would start with the coolant sensor as stated.
12:1 Infrared Laser Thermometer

 

[Endlessblockades]

164 degrees? Brrrrr, I'm confused, but I won't miss an opportunity to say: Use an OEM T-Stat with the jiggle valve at 6 O'clock! There, I feel better. Worked wonders for me - hope you get the issue sorted soon.

 

[Bad Luck]

There are two different/separate coolant temp sensor. One for the ECM and one for the instrument cluster gauge. The scangauge gets the coolant temp from the ECM. The instrument cluster gets the coolant temp from the other temp sensor.

EDIT: Added info. "FSM lists 2 sensors, one is located at front of engine next to the fuel rail cross overpipe ,this one goes to the computer.The second one tells the dash gauge the temperature, location not supplied by FSM.It indeed is at rear of engine as some have correctly implied,the main engine wiring harness is directly over it and surrounded by heater hoses and vacumn lines.I have only seen it thru a mirror! Thanks for the help" from this post: https://www.toyota-4runner.org/1830207-post13.html

 

[gamefreakgc]

Two different sensors. The ECT (engine coolant temperature sensor) sensor is located in the front of the engine under the intake plenum on the lower intake manifold. Close to the knock sensor harness pigtail connection, there's two connections there and one is for the ECT. This sends data to the ECU.

The second sensor, sometimes called the engine coolant temperature sender, is a single wire sensor on the water bypass section on the back of the engine near the firewall. Like mentioned you'll need a mirror to even see it. It has an odd "clip" type connector that isn't used anywhere else in the engine or the entire vehicle, for that matter. It's very easy to tear down the top end and miss this connector altogether as the lead from the engine harness is very short. Can be damaged or utterly forgotten on re-assembly. Make sure this connection is secure. If yes, replace the sender. If no, double check the dash cluster is connected securely as you just had it apart and are now having issues.

 

[Antznyopantz]

Update:

Replaced the rear sensor. Cranked it up. Gauge read "high" long before the scangauge made it to 180.

At scangauge 183 the thermostat opened right on time.

Tried another entire dash gauge cluster. Temp gauge almost immediately went up to "high" and stayed there.

It is reasonable to assume that the Scangauge, cluster, and sensor are good.

I allowed the vehicle to run with the radiator cap off and the heater on for a good 20 minutes at least. It was on jackstands with the nose elevated. There were no bubbles coming from the radiator. Top temp on the scangauge was 188 if memory serves.

Any ideas appreciated. Thanks!

 

[Bad Luck]

Replaced the rear sensor. Cranked it up. Gauge read "high" long before the scangauge made it to 180.

At scangauge 183 the thermostat opened right on time.

Tried another entire dash gauge cluster. Temp gauge almost immediately went up to "high" and stayed there.

It is reasonable to assume that the Scangauge, cluster, and sensor are good.

I allowed the vehicle to run with the radiator cap off and the heater on for a good 20 minutes at least. It was on jackstands with the nose elevated. There were no bubbles coming from the radiator. Top temp on the scangauge was 188 if memory serves.

Any ideas appreciated. Thanks!

I would assume the scangauge and ecm temp sensor are good. What does the instrument cluster show if you unplug the other sensor?

 

[Antznyopantz]

By "unplug" I am assuming you mean to unplug the wire from the sensor in the rear of the engine. My guess is that without signal it should go cold. It will be interesting if not!

I'll go try and report back.

 

[repo]

You tried with an entire new cluster from the same year or just a new board? It sounds like something on the back of the board maybe, a burnt out component maybe. Different years have different boards too. Or a ground problem maybe?

 

[Antznyopantz]

I would assume the scangauge and ecm temp sensor are good. What does the instrument cluster show if you unplug the other sensor?

I unplugged the rear sensor to the gauge cluster . The temp gauge read normal - smack in the middle and did not move. I tried it with both cluster gauges. Same result.

I also managed to rip the wire out of the paddle connector for my trouble.

I'll add it to the list. :bravo::banana:

 

[Antznyopantz]

You tried with an entire new cluster from the same year or just a new board? It sounds like something on the back of the board maybe, a burnt out component maybe. Different years have different boards too. Or a ground problem maybe?

I tried another entire cluster from the same year. I bought a parts car a bit ago. It has saved me time and money like wow.

The ground problem idea is interesting. Any clue where this one grounds to?

 

[repo]

I tried another entire cluster from the same year. I bought a parts car a bit ago. It has saved me time and money like wow.

The ground problem idea is interesting. Any clue where this one grounds to?

It should say in the FSM somewhere. I dunno. But should be an easier thing to check first than trying to replace that other sensor from the sounds of things.

 

[repo]

I tried another entire cluster from the same year. I bought a parts car a bit ago. It has saved me time and money like wow.

The ground problem idea is interesting. Any clue where this one grounds to?

Google "EWD471U parts pdf" for diagram.

Edit: The second sensor (gauge sender) IS the the ground as far as I can tell so nevermind ha. The one at the back of block. It should have one green wire coming out. "W 2" on the diagram. If its grounding on something else it would register the dash gauge at max. So I'd say its prob the wire coming out of that thing is damaged or loose.

 

[Antznyopantz]

With the ECT gauge reading in the correct range - how likely is it that this is a head gasket issue?

I noticed today that the overflow bottle looks lower than yesterday. I've been losing coolant monkeying with it with the cap off, but I don't know how much...

Thanks yall!

 

[nissanh]

Still got air traps

The missing coolant might have replaced any air bubbles inside the engine.

 

[Antznyopantz]

Problem solved.

I had previously reseated the gauge needle when I replaced the background to the gauge cluster. I put it at the "L" while the factory had put the needle going all the way to the bottom. That little bit at the bottom made a huge difference.

I did use a second gauge cluster to verify the first, but I'll give you one guess who had reseated that needle as well. :embarassed:

Lucky I had a third one on hand that had not been corrupted. It read just below center of the gauge. Perfect

Yeah I feel a little foolish.

It was an old-timer at my local auto parts store that insisted that the engine was not overheating and that having two bad gauges was entirely possible. The other clue was that the gauge went to halfway when I unplugged it. I don't know if that is what is supposed to happen - but it got my mind to the answer.

Anyway. Thank you guys so much for your help! I sincerely appreciate all the brain power!

 

[repo]

Problem solved.

I had previously reseated the gauge needle when I replaced the background to the gauge cluster. I put it at the "L" while the factory had put the needle going all the way to the bottom. That little bit at the bottom made a huge difference.

I did use a second gauge cluster to verify the first, but I'll give you one guess who had reseated that needle as well. :embarassed:

Lucky I had a third one on hand that had not been corrupted. It read just below center of the gauge. Perfect

Yeah I feel a little foolish.

It was an old-timer at my local auto parts store that insisted that the engine was not overheating and that having two bad gauges was entirely possible. The other clue was that the gauge went to halfway when I unplugged it. I don't know if that is what is supposed to happen - but it got my mind to the answer.

Anyway. Thank you guys so much for your help! I sincerely appreciate all the brain power!

Ha I did that also to get rid of bubbles in the backing behind the tach. I had to try and pin the needle in the right spot while looking at the info from the OBD2. It's still off slightly. Glad you got it figured out.