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2007 Voodoo blue FJ cruiser
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Discussion Starter #1 (Edited)
I’ve been using this forum for years, and finally I’ve found a problem that a previous post can’t fix! (Trust me I’ve read through all the overheating threads I could find).

My problem is this: the FJ overheats when driving at high speeds (ie, over 70mph). It’s an old FJ, a 2007 with 250,000 miles. This is its second engine, but this engine has been working fine for a few years now with no issues. It usually stays at about 190-199F. (I have an ultra gauge) It will stay about this range until I reach 75mph, then after a little while at that speed the temp will quickly spike to over 235F.

I first replaced the thermostat. No change.
A coolant pressure test showed the water pump is slightly leaking, so I replaced the water pump. No change
My bank 1 catalytic converter has been throwing codes for the last several months, so I thought the engine temp may be due to backpressure from a collapsed cat. Replaced that. No change.
I then tried cleaning the radiator. No change.
I then replaced the radiator. No change.

I’m now pretty deep, both in money and time, into this trying to figure out what the problem is. Do any of you guys have any ideas? I’m no mechanic, but I can’t think of anything else to go to: possibly it’s a serious engine issue of some kind? Maybe a cracked head gasket?

Any and all opinions, positive and negative feedback, is welcome!

UPDATE / SYNOPSIS:
(6/18/2020)

Things I've done so far:
1st replaced thermostat. No change
2nd replaced water pump. No change
3rd replaced radiator cap. No change
4th cleaned radiator. No change
5th replaced radiator. No change
6th replaced previously known broken catalytic converter. No change
7th replaced fan clutch. No change.
8th replacing headgasket currently.. (???)

System has been burped several times for air. Never any serious amounts of air in the system.

Old coolant has been replaced by all new

Oil is in good condition, 2500-3000 miles old (amber and clear, like bourbon)

Not the original engine, but oem from a wrecked FJ. “New” engine had 60,000 miles on it when installed, I’ve put 40,000 on it since with no issues.

No engine, cooling system or drivetrain modifications besides a tranny cooler.

I am running 285/75r17s, and have an ARB with some lights. So some engine load/air blocking, but nothing crazy by any means.

Mechanic believes its a head gasket issue. Overflow tank appears not to drain back into the engine. Only gets hot at high(ish) rpms over 3,000. (ie going down the interstate at 75-80). Under normal driving conditions, around town, no overheating has occurred yet

Rechecked thermostat, no change, nothing wrong there.

HEAD GASKET APPEARS TO BE THE ISSUE
Shop pulled the heads, noted they are warped and the gasket is in pretty degraded shape. Our theory is the replacement engine sat unused for several years, and the gasket rotted and cracked from not being ran, pressurized, and used. Currently the truck is being worked on and the heads are at the machine shop.

TIMELINE
problem first appeared while towing, temp hit 203F
Next day hit 209F
Next week consistently hit 218F
Hit 230F, took to mechanic first time.
After cats had been replaced, took the FJ back and it promptly overheated again, this time after working fine for a day or two, temp spiked quickly from 199F to 240F in a matter of a minute. Pulled over and returned to mechanic, now considering head gasket replacement, selling the truck if the problem can’t be located.
Engine overheated for a 3rd time, symptoms more inline with a headgasket issue. Currently the shop is testing more in-depth for a blown headgasket.
Shop confirmed headgasket is leaking, the heads have been pulled and are being machined and a new gasket is being put on. I’ll update after I get it back and drive some.
 

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Could your timing be off a bit? I had a timing chain off by a link and it would get hot fast. Maybe drive no faster than 70mph?? I find mpg really sucks once im over 70 mph anyway :)
 

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Replace the thermostatic clutch on the cooling fan. After a failed thermostat, this is the next-most-likely thing to fail at 250K miles.

A water pump will eventually start to leak as the seal fails, or get noisy and then 'wobbly' as the bearing fails, but it will continue to pump water (unless it has a plastic impeller that disintegrates).

Grossly incorrect ignition timing or grossly lean mixture can also be factors, but both are unlikely with the ignition and fuel injection systems used on this engine.

A failed head gasket is potentially another cause ... do you see white smoke on initial startup with a cold engine, or a continuous loss of coolant?

Replacing the water pump, catalytic converter, and radiator were just costly blind guesses without any evidence indicating that they were defective in any way.
 

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2007 Voodoo blue FJ cruiser
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Discussion Starter #4
The water pump was known to be leaking, and I have been pulling error code 0420 for a bad cat for some time now, so I replaced those hoping to fix the problem but knowing that if it didn’t, I’d be knocking other problems off the list. The thermostat and the radiator were indeed guesses tho! Lol

It doesn’t seem to be a head gasket, there is no coolant in the oil and no smoke. I might try some of that stuff you put in the coolant to see if there is exhaust gases in it, as another check.

I’ll defiantly look into the fan clutch. Is there any symptoms of one that might give it away as the clutch? I read here, if it spins freely it’s a sign it’s bad?

Another bit of information: after replacing the radiator and water pump, the problem did seem to go away, for a day. But it came back very suddenly. I was cruising down the interstate, convinced I had fixed the problem, then out of no where after driving at 70 for 30 minutes, it spiked from 195F to 240F. I wonder if when I replaced the water pump, the higher coolant pressure caused by no leaks in the pump caused something else to blow out. I’ll check when I get home from work.

(and yes, maybe I should just drive slower than 70 lol) as for the timing chain, it’s very possible. It is not the original engine, after all. Tho I would need a mechanic to look into that- tearing my engine down is a little above my ability!
 

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Replace the thermostatic clutch on the cooling fan. After a failed thermostat, this is the next-most-likely thing to fail at 250K miles.

A water pump will eventually start to leak as the seal fails, or get noisy and then 'wobbly' as the bearing fails, but it will continue to pump water (unless it has a plastic impeller that disintegrates).

Grossly incorrect ignition timing or grossly lean mixture can also be factors, but both are unlikely with the ignition and fuel injection systems used on this engine.

A failed head gasket is potentially another cause ... do you see white smoke on initial startup with a cold engine, or a continuous loss of coolant?

Replacing the water pump, catalytic converter, and radiator were just costly blind guesses without any evidence indicating that they were defective in any way.
If the clutch on the fan failed and at higher speed how would it fail. If frozen my experience has been a very noisy fan noise but large volume of air still getting through radiator. If it failed to engage would that not be a problem at low speed with less air not going through radiator.
 

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A free-spinning fan when the engine is cold is confirmation that the thermostatic clutch has lost its silicone fluid.

Normally at a COLD startup, if you just let the engine run for 2 minutes at high idle, at first you will hear a very significant amount of fan airflow noise (roaring), as the fan clutch is locked up and the fan is turning at full pulley speed. Within a minute that roaring noise should suddenly diminish as the clutch starts slipping, and fan speed drops.

If your timing chain had 'jumped a tooth', you would have the CEL turned on and a full instrument panel of warning lights.

How many miles do you have on the air/fuel and oxygen sensors? If more than 85-120K miles, it's far more likely that a worn out exhaust gas sensor (~$100) was the real root cause of your P0420 ODB code, not a 'failed' cat. The information provided to the ECU on catalytic converter efficiency is only as good as the sensors that are measuring the composition of the exhaust gas.
 

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If the clutch on the fan failed and at higher speed how would it fail. If frozen my experience has been a very noisy fan noise but large volume of air still getting through radiator. If it failed to engage would that not be a problem at low speed with less air not going through radiator.
I've never seen a fan clutch fail in a 'locked-up' mode, only in the 'continuous slip' mode due to loss of fluid, or bearing failure where the entire fan wobbled.

Agreed, this case is a little unusual because with a fan clutch failure it's more common to overheat at extended idle, rather than at high speed where you should be getting plenty of ram air flow.

Replacing the fan clutch was suggested because it's a known high-mileage failure, it's inexpensive, and it's very easy to replace.

One underlying assumption here is that during radiator replacement the OP verified that the AC condenser was completely clear of accumulated debris and was not restricting airflow in any way.
 

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I've never seen a fan clutch fail in a 'locked-up' mode, only in the 'continuous slip' mode due to loss of fluid, or bearing failure where the entire fan wobbled.

Agreed, this case is a little unusual because with a fan clutch failure it's more common to overheat at extended idle, rather than at high speed where you should be getting plenty of ram air flow.

Replacing the fan clutch was suggested because it's a known high-mileage failure, it's inexpensive, and it's very easy to replace.

One underlying assumption here is that during radiator replacement the OP verified that the AC condenser was completely clear of accumulated debris and was not restricting airflow in any way.
Wonder if he could control the temp somewhat by turning on the heater?
 

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Fan clutch wouldn't matter at 75 mph... I would say radiator, as I had a vehicle that got hotter the faster it went - which I found odd - but a new radiator fixed it entirely. But you say you've replaced the radiator....
 

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2007 Voodoo blue FJ cruiser
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Discussion Starter #10 (Edited)
I had my cats efficiency checked by a trusted shop, and they did show a somewhat significant drop. So they were at least going bad (if not bad already). And for me, moving to a state that has emissions tests might be in my future so I wanted cats that work! Hence replacing the cats. It was this overheating issue that finally persuaded me to push forward and fix them.

I looked over the AC condenser and it appeared to be clean. I also haven’t been in deep mud recently and there isn’t any real reason for it to be dirty, but it’s always a possibility. I do have a transmission cooler, but that’s been on there for years and has never caused any issues before.

One of my co-workers, who’s a drag racing guy, mentioned he’s seen the interior of coolant hoses become frayed and develop flaps of rubber that can bend back and impede coolant flow at certain speeds. Seems pretty far fetched, but possibly something like this may be at fault? It would be hilarious if I chased this problem all over creation and it turns out being a coolant hose. I’m might look into that next.

The heater does work, and it does help lower temps somewhat when I have it on full blast.

The FJ is at the shop right now, I’ll keep you guys updated!
 

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Yeah, if you are certain that the AC condenser is clear and the thermostat is good, then looking for any restriction in the hoses (or any other place in the cooling system) is another thing to check.

Are these still the original hoses at 250K miles? If so, change them out!

The new thermostat was a Toyota OEM part?

Have you changed coolant at any point in the last few years? 50:50 Toyota red:distilled water?

I haven't seen coolant delaminate a hose and fold a big flap into the interior, but I have seen the interior of hoses deteriorate and 'crumble', shedding small chunks of rubber into the system. Usually in the end of the hose where the hot coolant first exits the block.

I'd reverse-flush the system into a big bucket, looking for any type of debris that might get flushed out, and then replace the hoses & new coolant.
 

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Wonder if he could control the temp somewhat by turning on the heater?
That will work to a limited extent, seeing as the heater core is only about 10% if the size of the radiator, but would be SUPREMELY uncomfortable!

I can remember my dad doing this 60 years ago with a brand new Ford Falcon station wagon as we climbed up the grade to Big Pine Lodge in the Sierras above Bishop. Engine was running very hot (but not boiling over). I was in the front passenger seat, and even though I pulled my legs up onto the seat, it was hotter than hell. I remember asking him why he had the heater on when it was 80F outside.
 

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Discussion Starter #13
Yeah, if you are certain that the AC condenser is clear and the thermostat is good, then looking for any restriction in the hoses (or any other place in the cooling system) is another thing to check.

Are these still the original hoses at 250K miles? If so, change them out!

The new thermostat was a Toyota OEM part?

Have you changed coolant at any point in the last few years? 50:50 Toyota red:distilled water?

I haven't seen coolant delaminate a hose and fold a big flap into the interior, but I have seen the interior of hoses deteriorate and 'crumble', shedding small chunks of rubber into the system. Usually in the end of the hose where the hot coolant first exits the block.

I'd reverse-flush the system into a big bucket, looking for any type of debris that might get flushed out, and then replace the hoses & new coolant.
Thanks! unless the previous owner changed them, they probably are! I’ll look at them and change them out.

As for changing coolant, I have a few times but I’ve never used OEM concentrate, I’ve always used pink premix for Japanese cars (but not made by Toyota). It’s never troubled me before but I’ll try the OEM stuff.

The thermostat was not Toyota OEM. I can confirm that. Possibly this new one failed on me? If that does end up being the problem, this is a perfect case study of why you should always go OEM lol
 

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just shooting in the dark here, but wondering if there is some type of airflow issue since it happens above 70 mph. Is the radiator shroud in place? Did you change anything in the front end around the radiators that would change the airflow from the OEM radiator setup. Does it overheat if you go 70 mph while in 4th gear versus 5th gear?
 

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I wasn't suggesting that the coolant brand could be an issue, just the difference in heat transfer capacity of a 50:50 mix vs straight glycol. Your pink Asian-vehicle compatible coolant mix should be fine.

I would have a slight concern with the non-OEM thermostat, just to ensure that it is physically the identical size & shape as the OEM part, has the same opening temperature rating, was installed in the correct orientation, doesn't hang up on any part of the thermostat housing, etc.

But the overheating problem existed BEFORE any of the cooling system parts were replaced, correct?

The slightly unusual 'reversed' symptoms (cools OK at idle, only overheats at higher speeds/loads) hints at an airflow or coolant flowrate problem.
 

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That will work to a limited extent, seeing as the heater core is only about 10% if the size of the radiator, but would be SUPREMELY uncomfortable!

I can remember my dad doing this 60 years ago with a brand new Ford Falcon station wagon as we climbed up the grade to Big Pine Lodge in the Sierras above Bishop. Engine was running very hot (but not boiling over). I was in the front passenger seat, and even though I pulled my legs up onto the seat, it was hotter than hell. I remember asking him why he had the heater on when it was 80F outside.

Heat transfer rate is proportional to the heat difference; if you're overheating, turning the heater on will pull a lot more heat out of the system than if you switch it on at a normal temperature.

I had to run the heater at full-tilt with the windows open in direct sunlight uphill in the San Juan mountains one year, with people behind me and nowhere to pull off and stop. Can confirm that using the heater as a last-ditch cooling solution works but is SUPREMELY uncomfortable.

If you try this and it works to decrease the temperature, you know that some parts of the coolant system are working fine: the part that's inside the engine block and in the heater (this probably includes the coolant fluid). That (probably) leaves just the main radiator, the fan, the thermostat, and its hoses as possible culprits. Maybe the pump? I don't know if the heater system has a separate pump from the main system.
 

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Discussion Starter #17
just shooting in the dark here, but wondering if there is some type of airflow issue since it happens above 70 mph. Is the radiator shroud in place? Did you change anything in the front end around the radiators that would change the airflow from the OEM radiator setup. Does it overheat if you go 70 mph while in 4th gear versus 5th gear?
I do have an ARB bumper. I wonder if this restricts airflow enough to cause any issues? I’ve never heard of that being a problem but who knows. Maybe I’ll take the rock guard off and see if it helps anything.
I wasn't suggesting that the coolant brand could be an issue, just the difference in heat transfer capacity of a 50:50 mix vs straight glycol. Your pink Asian-vehicle compatible coolant mix should be fine.

I would have a slight concern with the non-OEM thermostat, just to ensure that it is physically the identical size & shape as the OEM part, has the same opening temperature rating, was installed in the correct orientation, doesn't hang up on any part of the thermostat housing, etc.

But the overheating problem existed BEFORE any of the cooling system parts were replaced, correct?

The slightly unusual 'reversed' symptoms (cools OK at idle, only overheats at higher speeds/loads) hints at an airflow or coolant flowrate problem.
I’ll take a look at the thermostat and make sure. It appeared identical to me, but I very well may have missed something. The problem did exist before I replaced any components, which makes me think that the thermostat wasn’t bad in the first place and the new one also isn’t bad. It’s just not that as a problem.

As for flow problems, that does seem like the issue. The fact that it stays at normal temps during city driving and other conditions hints that it maybe be a choke point somewhere that only effects operation during extremes.

Currently the truck is at my mechanics having a coolant pressure test done, I’ll have news on it hopefully tmrw.
 

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Cooling system pressure test would only detect leaks. You don't have any visible external coolant leakage, correct?

What other symptoms of true overheating are you seeing? Visible steam from the reservoir?

Are you absolutely certain that the cooling system is actually overheating?

Any chance that your coolant temperature sender is going bad, and providing a bogus output to the temp gauge?

Swapping out the sender is relatively cheap and easy, and at 250K miles, the original sender has thousands of heating/cooling cycles on it.
 

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I'm going to second the airflow question.
You say you have an ARB bumper, but what else do you have mounted up front?
  • Lights?
  • Winch?
  • What grille is on it?
  • Number plate?
  • Grille badges/other grille bling?

Do you have anything on the roof?
What grade oil, and how fresh is it?
Do you have an oil cooler?
Any engine mods?
Can you take a photo directly from the front?

Last question - You're on your second engine - what did the first one die of?
 
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