Sporadic Overheating Issue? (solution ongoing)

Need your thoughts! Yesterday after 40 minutes of driving I got out of my 4R, left it idling for 10 minutes, got back in and smelled something hot from my vents (ac was on) maybe like hot plastic or rubber, and looked down to see my temp gauge sitting at 3/4. Not climbing just sitting at 3/4. Outside temp was 75-80°. No notable performance issues of any kind preceding this so it was confusing to me. After turning it off & opening the hood: no oil or coolant spray anywhere, coolant levels are good, both hoses feel warm/hot, serp belt looks good, dipstick oil looks healthy no odd color or smell or levels. So then I restart to first check the fan it looks good, and use my BT OBD reader which is giving me no concern codes or anything. Again, engine temp parks at 3/4 no climbing so I want to drive to find out if it’s a fan issue: so then as I put it in Drive the temp drops straight to 1/2(just barely below) where it’s normally operating. Yes, before I drive that happens and then I drive away. And my wife and I go to a few more places and I’m seeing if the issue will replicate by idling or anything and I cannot make it replicate. Now this morning coolant reservoir levels have dropped to about half-full. Any ideas?

bonus info if you made it this far: our last 3 days had been 9 hour drives and this was our first day in our destination. So 3 days of intense use long days on highway and then on this light use day at our destination this happens? Seems odd to me. Also, two days before our trip I noticed our AC having trouble keeping up sometimes after idling too long in hot weather +85. This is the part really has me wondering if the radiator fan isn’t slowly starting to go?

 

When you put it in Drive and the temperature dropped tells me that it was the transmission fluid. Not sure what is the point of leaving it idling so long? If the air conditioner cannot keep the cabin cool because of hot transmission fluid, what is the point of leaving the truck running?

 

Hmm good thought. I’ll keep note of that. The air conditioner can keep up almost all the time and was still blowing cold here. Reason for idle here was simply getting out to talk to a friend and then conversation runs on and I didn’t think to turn it off because I’ve never dealt with overheating. Any cause for transmission getting hot like that? Not a terribly hot day, no mountain driving, and hadn’t been driving for more than an hour.

 

I may have seen on YouTube in a video by The Car Care Nut (a Toyota Master Mechanic) Things Never To Do where he talks about things not to do with an automatic transmission. Others may chime in here, but the transmission needs fluid circulation for cooling. In Park or Neutral the fluid circulation may be reduced, so the temperature in the fluid rises, especially after a long freeway drive or extended idling period.

 

I would check the coolant level.

 

Coolant levels are referenced in post. And as per transmission I’m open to the possibility, but it would be incredibly odd after 3 days of long drives with plenty of idling without overheating. I’ll add that to my watchlist certainly though.

 

Missed the coolant part.

I don't know why Toyota didn't add trans coolers to these but freeway driving would only produce a ton of heat if you are gear hunting or driving with the convertor unlocked. All I can say is keep an eye on it. The issue could be electrical as well like a bad sensor or connection.

 

Coolant level will fluctuate depending on hot/cold engine. How many miles? I would pressure test cooling system and look for leaks. Off the top of my head-bad water pump, fan clutch going bad.

 

Check out this video and then reinspect the fan clutch.

https://m.youtube.com/watch?v=vgWJN4EEl-U

 

Thank you for all this input^ I just finished an hour on the interstate and temps were solid and I stopped to check coolant levels at 30 minutes and just now at the end of the drive and its remaining pretty much identical right at about half-full reservoir. Before yesterdays episode it was always right at the Full line anytime I checked so looks like I used up some coolant with that episode but now stabilized again? I’ll continue to keep an eye on it and update.

 

https://www.4runners.com/threads/a-...in-a-4runner-limited.8250/page-16#post-173786

 

I’m so sorry be that lazy internet guy, but I’m camping with intermittent service opportunities is there something specific I should be reading looking for in this thread/page. If the answer is “read the whole thing lazy internet guy” then I’ll do my best asap. Edited: read the part of the random overheat and my radiator face does have some bug build up but definitely nothing big, however you just put “go to hand wash car wash” for the first thing on my to-do list when I have the chance and I will absolutely make a point to clean out the radiator face.

 

Possible it could be debris, but it would be more consistent I would think. How many miles?

 

Maybe a sticky thermostat.

Other possibilities;
leak in cooling system
blockage in the cooling system (airflow or internal)
intermittently bad fan clutch
belt slipping maybe due to a bad tensioner

Once it gets hot outside my 4 Runner idles at least an hour every day, sometimes much more.

 

This seems similar to where I’m at in my guesswork until it repeats itself or I take it in for proper diagnoses.

 

two days since the initial “overheat” - yesterday never idled for long and no issues at all - today I was gently attempting to replicate the issue so I drove about 10 minutes (up to temp), left it idling for 10 minutes while I ran an errand and left my wife to oversee the temp, I came back no issues but the AC wasn’t blowing as cold. Drove a couple streets to my next errand and left idling 10 more minutes and came back to see the temp slightly above half way. Started driving again and after two minutes we were back at standard temps. outside temp was 80-85°. It’s really making me think the fan is having trouble keeping up… will likely go for a diagnosis once I have the ability. Also want to clean the radiator face from thousands of miles worth of highway bug&debris.

 

Did you test the fan clutch for play and free spin?

 

I didn’t yet, but I will do that once it cools down again. Thanks for the tip to check that!

 

At the risk of sounding like an idiot, is 3/4 on the gauge really "overheating"? I mean, temperatures fluctuate, hence the gauge existing in the first place, and unless the engine was literally overheating I personally would not worry about this apparent one time deal. If it is a problem you'll know it soon enough and if it isn't a problem you will drive yourself crazy trying to diagnose it and interpret micro changes on the gauge.

 

Agreed; if it doesn't get into the red section, it's not really a problem.

Or, you could take the opposite approach and buy an Ultragauge, and continuously monitor engine and trans tenps, and wonder why it's 189 instead of 185, or 181, or 195, and really drive yourself crazy.

 

I agree with you, I did use "overheat" with quotes just a couple comments prior because yes not until it hits the red. That said, in my view if I've got any machine/equipment acting abnormally I tend to pay attention. Hence, if my 4R always operates at temp just below half on the gauge and then it decides to run up near 3/4 for no apparent reasonable cause and especially in conjunction with other symptoms (a/c issue) then I've got flags. But that's just me! I've driven plenty of beaters that have had known issues (actually a '94 chevy blazer would regularly run hot, no biggie, add more water lol) but this is the nicest vehicle I've ever owned and if it behaves irregularly I pay attention. Largely in hopes that I can track down the issue myself, also if needed I can explain and replicate the issues for a mechanic to make life easy. Posting on here is helpful in case anyone says "oh I had this exact thing happen - here was my answer"

 

I have a scangauge and can tell you that the water temperature gauge on the truck doesn't move at all between 180-195. I'm guessing you'd have to be close to 210 or more for it to start moving the needle to the 3/4 range like the OP saw.

 

After reading this it brings to mind something I experienced on a different vehicle and thought it might be helpful. But first, a question: Are you the original owner, and if so, has the water pump ever been replaced? If so, was it a factory Toyota water pump or aftermarket purchase somewhere else than Toyota?

I say this because on a different vehicle I owned, I had to replace a water pump purchased from the aftermarket due to circumstances and lousy timing because of a major holiday weekend. I needed the car to get to work, and the dealer parts counter was closed on the actual holiday. The aftermarket pump was purchased from a retailer like Auto Zone or similar. When comparing the removed pump impeller with the aftermarket pump impeller, the OEM pump impeller was substantially larger in diameter and the impeller "blades" that push the coolant had a much smaller area. With the aftermarket pump installed, the cooling system performed okay as long as the car was moving and engine RPMs were high enough to move enough coolant. But when the car was not moving with the engine idling, the temperature would rise after some minutes, and keep rising until the car was moving enough with higher engine RPMs to move more coolant.

I fixed this problem by going back to an OEM water pump a few days later.

 

I was able to run the impromptu fan clutch test (UPDATE after solution: I now wonder if either A) I did this cold so I got resistance? or B) if I just don’t have enough experience because my mechanic who works quite a bit on older trucks guaranteed me it’s the fan clutch which now seems to have solved the problem and he said he can just tell by feel with fan clutches after doing so many) and I still get plenty of resistance so I’m lowering that on my list for the time being. Now your water pump story has me very interested because I’m the 2nd owner and I don’t know that it’s been replaced but I’m at 180k so it’s possible. I’ll do some more checking on this over the next couple days and circle back.

 

OP, you said you checked with your OBD2 BT to see if there were any codes.....does it not also display the engine coolant temperature, mine does and it's not an expensive one?

If so why didn't you check it to see what the temperature was on it??

Check the bottom of the waterpump for the "weep" hole to see if it's/wet/ has been leaking, all water pumps have a weep hole on the bottom of the shaft part of the housing, coolant coming out of the weep hole is the first sign of a waterpump going bad, i.e. it's the shaft seal that usually goes bad before the shaft bearing, when the seal goes bad coolant will come out of the weep hole.

 

This just happened to me. When idling, gauge would creep up but not go into red. AC was not keeping cool. When I would drive, needle dropped down to halfway point and AC was working fine. Took it in and there was debris accumulation I want to say in the coolant but could be wrong. I do know it wasn't a part or anything mechanical that needed replacing. Anyhow, it was stopping the airflow while in idle but when moving, air was moving so it was cooling. Cost was around $600. Didn't sound like a hard fix, I'm just not a mechanic. Whatever it was, it worked. Hope that helps.

 

I’m hoping this is my final update. Fan clutch has been replaced (there was no specific YT vid so I made one) and we’ve had a few 90° days already to test the idle heat build up issue… no problems so far! This issue started mid-June last year and by the end of August I would get nervous if I went to a drive through above ~80° because the temperature would start creeping up if I had to wait. So I feel somewhat confident that the issue is resolved now that I can consistently idle in 85+ temps in direct sun with no apparent issues.

will update this thread if for any reason the issue returns!

 

Thank you for coming back and updating what you found.

 

Weeellll, I was hoping this thread was dead... but today in a parking lot, a sunny 85º day, the engine temp started slowly creeping upward to about 2/3rds on the gauge and with one quick loop around the parking lot the temperature dropped again no problem. Few minutes home, pop the hood & crawlin' under, I see no leaking on the engine to indicate water pump seeping, coolant overflow levels are perfect so it's not inhaling it (head gasket) &/or leaking it bc there's also no leaking around radiator seams or anything. Truly mysterious still, a bit bummed. Only two other symptoms I can suspect as real possibilities right now: my coolant is near due for change (but I don't think that's the issue) oorrr thermostat is partially failing? It doesn't seem likely or common, but a sticky thermostat spring could be the culprit here to explain it being intermittent. Because it's so affordable & easy I'll go for the thermostat first and continue to monitor. If that doesn't solve it then I'll probably do water pump and no matter what I'll do coolant flush soon anyhow.

 

Thermostat is definitely something to check.