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There is a sweet aftermarket radiator with extra capacity that is on my mod list.

Under armor traps heat and can cause overheating in the engine compartment, especially if moving slowly.

Exhaust also can cause issues. We have 4 cats that create a lot of heat. Alabama has no smog checks. Looking forward to yanking them out and cooling down the engine and driveline spaces.
 

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2007 Voodoo blue FJ cruiser
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Discussion Starter #22
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.
i have no visible symptoms. Only my ultra gauge and my dash gauge. The shop replaced the sensor and it still has been overheating. They’re completely stumped as much as we are. They did notice the overflow reservoir was very full, and they’re wondering if it’s overflowing but the reservoir is clogged and isn’t letting coolant back into the engine. So today they’re breaking into that and looking.


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?
I have an ARB with a front plate, no winch. I have two lights ontop the bumper, as well as the stone guard, stock grill with no bling. Nothing crazy.

I do have stuff on the roof, including a shovel and some lights, on the stock rack. The oil has less than 3000 miles on it, and I use valvoline synthetic. I’ve been anal about changing oil.

the old engine died of a serpentine belt breaking, and overheating. I was on the highway and by the time my dash lights came on, it was too late- I was stuck in downtown Louisville on I-64 during rush hour, and by the time I limped to an offramp to pull over (there’s no breakdown lanes) it had caused the block to warp. I never noticed the temp gauge go up until the lights came on. It sounds stupid because it was, on my part. I glance at the gauges constantly now lol!
 

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2007 Voodoo blue FJ cruiser
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Discussion Starter #23
0BCCC17A-B1DC-4F42-859E-232792147F70.jpeg
C4E8448E-4D22-4FC0-ABD5-5EBD34FCA4C8.jpeg

here’s the front end.
as for engine mods, I have none. I also don’t have an aftermarket oil cooler or anything.
 

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OK, both your instrument panel temperature gauge and your ultragauge are receiving their input from the same temperature sensor.

But you don't have any other signs of overt engine overheating, correct?

Do you have a non-contact IR thermometer that you can use to read the temperature of the thermostat housing, and the top radiator tank?

If you have a small diameter thermocouple you can loosen one of the radiator hose clamps, slide the TC into the hose, re-tighten the clamp and make a direct measurement of coolant temperature ... but not everyone has thermocouples laying around.

The high coolant level in the reservoir is a concern ... that can be one of the symptoms of a head gasket leak. Did you perform the test for hydrocarbon gas in the coolant?

What was the origin of the #2 engine? Factory new, or a 'used' engine?
 

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You
View attachment 1131772 View attachment 1131773
here’s the front end.
as for engine mods, I have none. I also don’t have an aftermarket oil cooler or anything.
You might be surprised how much of a wind shadow things like bumper lights create (try accelerating to 70mph, then put you hand a foot behind your wing mirror, then move it off to the side) the square bumper, the lights will be creating a pressure wave and seriously blocking airflow thru the grille. I'm gonna guess that if you take those lights and that plate off your problem is going to go away.
I had bumper mounted lights and noticed that the dust pattern on the grille was massively affected by them. At the same time, I moved my number plate so it wasn't blocking the lower vent.
The lights won't make any difference at low speed, but at high speed, the difference will be significant.
Give it a try and report back.
 

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OP, please confirm what I think you said initially: that your FJ ran fine for YEARS with the replacement engine, without any overheating, and that no modifications of any kind were made to the vehicle around the time that the overheating (at least according to the temperature gauge) first showed up.
 

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Old radiator hoses can callapse or to make it harder to find only callapse on the suction side of the pump while the pump is pumping a lot of water. One post said try to take out the thermostat and drive. That would be the first thing I would try along with really checking the hoses, especially the suction hose. With the thermostat out if you can see the suction hose rev the motor and see if it collapses. Also don't rule out exhaust, you have new converters but what about the rest of the exhaust. Look for Anything that could be restricting exhaust flow. Plugged mufflers smashed pipes. At 70mph air flow should not be the issue. You said a quick spike in temp. That keeps me going back to a hose. The hoses should be firm not soft. Hope you find your gremlin.
 

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Discussion Starter #28
You

You might be surprised how much of a wind shadow things like bumper lights create (try accelerating to 70mph, then put you hand a foot behind your wing mirror, then move it off to the side) the square bumper, the lights will be creating a pressure wave and seriously blocking airflow thru the grille. I'm gonna guess that if you take those lights and that plate off your problem is going to go away.
I had bumper mounted lights and noticed that the dust pattern on the grille was massively affected by them. At the same time, I moved my number plate so it wasn't blocking the lower vent.
The lights won't make any difference at low speed, but at high speed, the difference will be significant.
Give it a try and report back.
Will do, as soon as I get a chance! My mechanics are still giving it a look over
OP, please confirm what I think you said initially: that your FJ ran fine for YEARS with the replacement engine, without any overheating, and that no modifications of any kind were made to the vehicle around the time that the overheating (at least according to the temperature gauge) first showed up.
Yep! It ran perfectly fine for years. I’ve owned it since 2015, and the new engine has 75k miles on it.
Old radiator hoses can callapse or to make it harder to find only callapse on the suction side of the pump while the pump is pumping a lot of water. One post said try to take out the thermostat and drive. That would be the first thing I would try along with really checking the hoses, especially the suction hose. With the thermostat out if you can see the suction hose rev the motor and see if it collapses. Also don't rule out exhaust, you have new converters but what about the rest of the exhaust. Look for Anything that could be restricting exhaust flow. Plugged mufflers smashed pipes. At 70mph air flow should not be the issue. You said a quick spike in temp. That keeps me going back to a hose. The hoses should be firm not soft. Hope you find your gremlin.
It very well could be the hoses- I’ve heard that exact same thing from a few people. I’m in the process of replacing those right now. I’ll report back this afternoon when I get it back from the shop, if they found anything out!
 

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Will do, as soon as I get a chance! My mechanics are still giving it a look over


Yep! It ran perfectly fine for years. I’ve owned it since 2015, and the new engine has 75k miles on it.


It very well could be the hoses- I’ve heard that exact same thing from a few people. I’m in the process of replacing those right now. I’ll report back this afternoon when I get it back from the shop, if they found anything out!
Please have your shop SAVE the old hoses so IF they are confirmed to be the cause of the overheating, we can see exactly how they failed internally, while showing no external signs of distress.
 

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Discussion Starter #30
Please have your shop SAVE the old hoses so IF they are confirmed to be the cause of the overheating, we can see exactly how they failed internally, while showing no external signs of distress.
Will do! I’ll let you guys know as soon as I do. Turns out, no news today. I should have some info tmrw afternoon
 

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You say after the radiator change it worked fine for a day?
Did you drive it 70+ on this day and all worked as designed?
 

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Discussion Starter #33
You say after the radiator change it worked fine for a day?
Did you drive it 70+ on this day and all worked as designed?
It appeared to work fine- for awhile. I probably got 40 miles of highway driving on it before it got hot again. I was going about 75 on the interstate.
 

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This is were detailed and accurate notes on what had been tried/done and results help narrow down the problem.
My guess is something is restricting the coolant flow. I know that is a broad statement but from what you have posted thats what appears logical.
Guessing only and these kind of problems can sometimes be more than one issue.
 

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Discussion Starter #35
Okay, I have a slight update.

I got the FJ back from the mechanic, and he is completely stumped. So stumped, that he has waved the majority of the labor costs for all the work he’s done for me. He suspects it might be a head gasket issue, literally only because that’s the last part left to be changed. He was very clear with me that he doesn’t know, and a head gasket might get us nowhere. He did say he checked all the hoses, and found nothing wrong with them. He didn’t replace them tho. He said they all seemed fine, and probably weren’t the original hoses. I may just replace them myself this weekend for kicks and giggles. He also put 200 miles on the truck test driving it, and they couldn’t replicate the issue. I’m still pretty nervous about it because the issue is still at large with no definite fix. He recommended selling the thing and getting out from under it, because the truck may not be worth dumping another 2k in for a head gasket replacement. I’m mechanically inclined, but I have neither the tools, the time, the know-how, or the confidence to tear into my head gaskets.

I drove it for 50 miles today on the highway, no overheating. I travelled at 70 mph the whole time, never got up above 75 where the overheating issues happen.

Im pretty uncertain as to what my next step should be. What would you guys do if you were in my position? The truck has 251,000 miles on it, but is in PRISTINE condition (besides this problem) -I’ve babied it and taken amazing care of it. I’m not sure what I could sell it for, but the idea of getting my hands on a newer FJ and dumping this headache seems pretty attractive right now. I just can’t justify replacing the headgasket on a whim without being sure that’s the problem.
 

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Did you ever remove the thermostat? Maybe there is another way to see how hot it is really getting to confirm what you think? After market bigger radiator? Just a few thoughts...

<>< <>< <>< <*((^(((><
 

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OK, both your instrument panel temperature gauge and your ultragauge are receiving their input from the same temperature sensor.

But you don't have any other signs of overt engine overheating, correct?

Do you have a non-contact IR thermometer that you can use to read the temperature of the thermostat housing, and the top radiator tank?
THIS.

Drive and reproduce the issue, then pull over ASAP and use that thermometer to gauge and inspect the temperatures of everything you can think of involved engine temperature - hit the radiator cap, the coolant tank, the hoses, the transmission, the transmission cooler... and different locations on each. Write down the date, time, location, temperature, and what you did on the road to cause it. Good guesses have failed, so you just need to accumulate data and allow a pattern to emerge. That, and sanity-checking your temperature sensor.

Reflective surfaces are hard to get a good IR temperature reading on; you typically have to pay a lot more for an IR thermometer that can handle shiny surfaces. They'll report wrong temperatures if they aren't capable of handling reflective surfaces. Consider getting a reasonably-priced "probe" thermometer, too, with a probe on a long lead that you can stick up against shiny surfaces.

I had an overheating problem that was "mysterious" like this once upon a time, that defied coolant flushes, hose inspection, thermostat replace, etc. I went through many mechanic visits and corresponded with a Toyota Master Tech. In my case, it was clogged radiator fins. Since you've got a relatively-new radiator and that didn't change the issue, that's probably not the problem. But, the way that the clogged radiator fins manifested in overheating is interesting:

Only the bottom part of my radiator on my automatic-transmission FJ Cruiser was clogged. Specifically, mud had been baked into clay around the fins - so washing the radiator without removing it ran clean, so I thought it was OK... but essentially the fins were ceramic coated, crippling their ability to dissipate heat. This mostly corresponded to the entire transmission cooler (integrated into the bottom of the radiator assembly); the part of the radiator that cooled engine coolant worked fine. So what happened is the transmission would heat up and be unable to dump any heat, so the transmission fluid would just heat and heat and heat up... and when running through the radiator, it wouldn't conduct heat away into the air, but it would conduct heat through the radiator into the engine coolant. My clogged transmission cooler was putting heat into my engine coolant, through the engine radiator.

You mention "you have a transmission cooler" but it's never been a problem. Do you have an Automatic or a Manual FJ? Regardless, when you are measuring everything's temperature, be sure to include all your radiators - transmission, A/C, and engine - in your temperature tests.

You may need to pull out all of the parts and inspect them yourself, if multiple mechanic trips aren't figuring it out. If you do this, take multiple pictures from different angles of each part after you remove it, and store those photos somewhere with the date. Worry about that after you've got a set of thermometers and have measured everything during an overheat event.

Also consider: Updating the original post in this thread with a nice summary of everything you've tried and what the result was, so that as the thread goes on and on folks - yourself and other forum members - don't lose track of what you have and haven't tried.
 

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Discussion Starter #39 (Edited)
THIS.

Drive and reproduce the issue, then pull over ASAP and use that thermometer to gauge and inspect the temperatures of everything you can think of involved engine temperature - hit the radiator cap, the coolant tank, the hoses, the transmission, the transmission cooler... and different locations on each. Write down the date, time, location, temperature, and what you did on the road to cause it. Good guesses have failed, so you just need to accumulate data and allow a pattern to emerge. That, and sanity-checking your temperature sensor.

Reflective surfaces are hard to get a good IR temperature reading on; you typically have to pay a lot more for an IR thermometer that can handle shiny surfaces. They'll report wrong temperatures if they aren't capable of handling reflective surfaces. Consider getting a reasonably-priced "probe" thermometer, too, with a probe on a long lead that you can stick up against shiny surfaces.

I had an overheating problem that was "mysterious" like this once upon a time, that defied coolant flushes, hose inspection, thermostat replace, etc. I went through many mechanic visits and corresponded with a Toyota Master Tech. In my case, it was clogged radiator fins. Since you've got a relatively-new radiator and that didn't change the issue, that's probably not the problem. But, the way that the clogged radiator fins manifested in overheating is interesting:

Only the bottom part of my radiator on my automatic-transmission FJ Cruiser was clogged. Specifically, mud had been baked into clay around the fins - so washing the radiator without removing it ran clean, so I thought it was OK... but essentially the fins were ceramic coated, crippling their ability to dissipate heat. This mostly corresponded to the entire transmission cooler (integrated into the bottom of the radiator assembly); the part of the radiator that cooled engine coolant worked fine. So what happened is the transmission would heat up and be unable to dump any heat, so the transmission fluid would just heat and heat and heat up... and when running through the radiator, it wouldn't conduct heat away into the air, but it would conduct heat through the radiator into the engine coolant. My clogged transmission cooler was putting heat into my engine coolant, through the engine radiator.

You mention "you have a transmission cooler" but it's never been a problem. Do you have an Automatic or a Manual FJ? Regardless, when you are measuring everything's temperature, be sure to include all your radiators - transmission, A/C, and engine - in your temperature tests.

You may need to pull out all of the parts and inspect them yourself, if multiple mechanic trips aren't figuring it out. If you do this, take multiple pictures from different angles of each part after you remove it, and store those photos somewhere with the date. Worry about that after you've got a set of thermometers and have measured everything during an overheat event.

Also consider: Updating the original post in this thread with a nice summary of everything you've tried and what the result was, so that as the thread goes on and on folks - yourself and other forum members - don't lose track of what you have and haven't tried.
Thanks! That’s a really good idea. I have an ir thermometer, I’ll throw that in and try to get it to replicate the problem. It is an automatic transmission.

After letting the FJ cool down, I went out at lunch and inspected everything. My oil is fine (Amber and clear- like bourbon)
My coolant overflow tank is almost completely full. When I left my home this morning it wasn’t quite as full. It’s raised about 1/2 inch.
I opened my radiator cap and noticed I couldn’t see any coolant. The radiator cap is located on an L shaped tube that empties into the radiator, and I couldn’t see any fluid up to the level of the bend. The top radiator hose is very squishy- I easily crease it all the way closer, and almost ball my fist around it. The bottom hose is pretty stiff, not at all like the top hose.

I noticed that there was coolant everywhere, probably draining from the coolant overflow tank’s overflow valve.

EDIT:
UPDATED ORIGINAL POST WITH ALL CURRENT PROGRESS.

I will keep updating the original post as I get developments, and with what I end up doing to fix this.
 

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I noticed that there was coolant everywhere, probably draining from the coolant overflow tank’s overflow valve.
"Probably"

But you took photos then cleaned it all off, so that you'll be able to tell if there are any new coolant "leaks," right? ;)

problem first appeared while towing, temp hit 203F
Only gets hot at high(ish) rpms over 3,000.
These clues say to me to make sure you have checked the transmission, transmission fluid, and transmission cooler well enough... From reading the summary and timeline, it looks like you haven't really dug into those yet. Your transmission cooler isn't gunked up or anything (inside or outside), right?

Automatic Transmission FJs have a portion of the main engine radiator dedicated to cooling the transmission - the little hoses out the bottom of the radiator. If you have an aftermarket transmission cooler, someone had to have disconnected those and... done something. Added your transmission cooler inline? Bypassed the original transmission cooler altogether? You mentioned you had your radiator replaced as part of this. Who did that? I don't suppose you have photos after your transmission cooler install and before the radiator replace just to double-check that the radiator replace didn't change anything out from underneath your assumptions about the transmission cooler?
 
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