Full size Toyota owners- Overheating question-
 

So Figured I'd post this here since there are a lot of Toyota owners here on RCC.

I've got a '99 4Runner ( 225,000 miles) and it recently developed an overheating problem. I was planning to replace the water pump and thermostat as I think that one or both of those things are the issue.

But after letting the vehicle sit for a month or so over the winter, I started it ( jumped it/ dead battery) and noticed that it was as if the transmission was slipping.

I've never had any issues with the transmission and I don't think that there is anything wrong with it now but any idea what's going on here? When I engaged it into Drive and Reverse, it slipped as if it was low on trans fluid. It doesn't 'feel' like an issue with the actual transmission.

So any words of wisdom here? Could the fact that the vehicle wasn't driven for a while have caused it to act like this? Trans fluid level appears fine but I'm just wondering if somewhere between the vehicle sitting for a long period of time and/ or combined with the possibly faulty thermostat and/ or water pump, if this might somehow have an effect on the engagement of the transmission?

Any ideas here?

Re: Full size Toyota owners- Overheating question-
 

Those trucks are infamous for the coolant and trans fluid mixing together because the trans cooler is built into the rad.


another thing to consider, that since the truck was over heating, the also means the trans fluid running through the rad was more then likely getting hotter then it should have been and if it hasnt been properly maintained over the years that could done some damage.


whats the fluid look like overall?

Re: Full size Toyota owners- Overheating question-
 

Always start with easy and inexpensive maintenance items; check all fluid levels (oil, coolant, transmission), thermostat (pay attention to temperature ratings), change coolant, flush the cooling system, replace hoses, check sensors (temperature, O2, air flow meter, or other than may effect air:fuel mixture)

Re: Full size Toyota owners- Overheating question-
 

Thank y'all both greatly.

Fluid visually looks reddish-brown... more red than brown but I'd be lying if I said it looked fresh. I haven't started looking at sensors nor have I flushed or replaced any fluids recently. Aside from regular oil changes, the vehicle has not been maintained very well. Last year I topped off the tranny fluid because it was a bit low... not severely low... just down a little from the 'full' line. Coolant was also a bit low last year so I added a 50/50 Dexron... OEM specd.

I'll add to this that a couple years ago the engine was running hot to the point that one of the hoses blew ( vacuum hose? heater core bypass?). It's a black plastic housing or module that's attached to the middle/ top of the engine bay on the firewall. *Image shown below* I replaced the hose and refilled with coolant and it was seemingly fine after that... until late last year when the temp gauge again showed the vehicle running hot. It never red-lined but that may not be here or there. At that time I looked at that module/ housing and noticed it was weeping/ dripping fluid... not sure if water or coolant.

I'm trying to not put too much money into this vehicle being that it's got fairly high mileage and I've been debating selling it prior to all of this anyway. I don't mind replacing the water pump ( and was going to replace the thermostat at the same time while I was in there) but if it looks like there may be a transmission issue, I may decide to let this girl go... idk.



https://i.postimg.cc/cLnnBp5Q/IMG-3732.jpg

Re: Full size Toyota owners- Overheating question-
 

Automotive tech here.

First and foremost, replace thermostat.. that's the first and most common cause of running hot.

Water pump, take the belt off and make sure the pully isn't loose (bad bearings) or leaking. If neither of those then like NOT the cause since toyota doesn't use the stupid coolants US brand do (GM products. Dexcool)

Pull the radiator cap and make sure there is no brown or milky build up. That's a sign of transmission fluid leaking into the radiator.

Make sure all belts are TIGHT, so none are slipping.

Check the clutch fan: first with engine cold it should move with a little resistance. Start engine let run for a minute, should here a roar from the fan for a minute or too till the fluid in it warms slightly.

Let the engine run and make sure fan is moving air good. Once the engine is warmed up to running temp, it should be blowing air pretty good. Shut engine off. Try to move fan again by hand, should have a good amount of resistance.

If the fan spins really free at point or not moving a lot of air (hear the mild roar) clutch is bad.

As for transmission, try driving it a fair bit, should come back if fluid is truly in good shape. But if any moisture or wrong fluid got put in, transmission may need fluid changed or be toast. Transmission fluid should have always been changed at no more than every 100k, more preferably around every 50k.

All that said, if you have been overheating it repetitively then you may have blown a head gasket.

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Re: Full size Toyota owners- Overheating question-
 

the toyota V6 also has a tendancy to blow headgaskets i have done more than my share of gaskets on those rigs my freind got his yota for free cause of the headgaskets it was cheaper to replace the motor than have some one do the gaskets on it lol go figure

Re: Full size Toyota owners- Overheating question-
 

Not for no reason they don't. I'm in 2 different toyota clubs, plenty with 250k+where the motors have 0 issues. Blown head gaskets are 95% owner caused, not an engine failure. Caused due to excessive over heating which happens on any aluminum head engine.

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Re: Full size Toyota owners- Overheating question-
 

Really appreciate the replies. I'm sort of on the fence with this one right now but I think I'm leaning towards letting it go. I won't be able to get much money for it without being able to even let someone drive it for more than about 10-15 minutes before it overheats. I know that I can get $500 for it. Guy wants to buy it for that and flat-bed it home. But I don't like the thoughts of potentially sinking much money into this vehicle at this point.

I've done plenty of work on vehicles over the years... shade-tree level I guess. But chasing issues with this one isn't appealing to me at the moment. I'm getting old and not in the best shape for doing too much wrenching these days depending on the scope of the job. If I thought that all would be good after installing a new water pump and thermostat, I'd do it. But knowing that there could be additional issues makes that tough to rationalize.

And to add to that I can only do so much here in my garage anyway due to space limitations. If I thought it was just a water pump or thermostat, I'd have done those by now. But I dunno... sometimes hard to justify chasing down repairs on an old heap. The engine has had a slight knock for a while now as well, leading me to believe that there really could be bigger issues.

Re: Full size Toyota owners- Overheating question-
 

for the record, I am a former Toyota tech, and while Toyota engines are notorious for their reliability and mileage conquests they are not without faults. the 3.4 is a great engine, however, in my experience after they crest that 225-250k mark I have certainly seen my fair share of them blow head gaskets...and it wasnt from people over heating them, they just went. Ive also seen 3.4s with 380k on them and the owners never done anything but change fluids and maybe 1 timing belt...


The water pump on your engine isnt as simple as something like a SBC, youre gonna have to pull the timing belt apart... its not a hard job, but if youve never done one it may be be some what difficult.


With that said, I would at the least do a compression test, or IMO even better would be a leak down test and thatll tell you a lot about the health of the engine. If your already on the edge of fixing it I woudnt waste the time and money on the T belt, pump, t stat if you arent going to check for a possible blown HG first.



Also, DO NOT sell that thing for 500$...if its clean and rust free youd be selling yourself short.

Re: Full size Toyota owners- Overheating question-
 

spoken like a yota owner lol

i always saw them around 150-200k for what ever reason and the only reason i saw them at all is cause they couldent aford to have a mechanic do the job and mostly cause they just bought the truck and got screwed by the po

having a rod knock and over heating sounds like it would be cheaper to do a motor swap my buddy payed 1500 for his rebuilt long block and 1500 to have it installed the same shop wanted 3k to do the headgaskets going with the new motor would atleast have a warrentyy with it

if you sold it for 500 it would be a great deal for sameone who can work on them if paying someone im guessing you could find a running driving rig for less than 3500 so maybe not such a great deal for some one who has to pay to have the work done

Re: Full size Toyota owners- Overheating question-
 

a vary simple head gasket test pop the radiator cap is the water right at the bottom of the cap if yes your probably fine if no there is a air leak some were go to step 2 with radiator cap off run the truck to operating temp fill the radiator to the top and look for bubbles if its a head gasket there will be a steady stream of small bubbles and will kinda froth up after a while
while its not 100% its a pretty good indicator theres a head gasket issue personaly ive never seen bubbles with out a blow gasket and it dosent cost anything to do the test or take any special tools just alittle time and might sway your decision to keep or sell the rig

Re: Full size Toyota owners- Overheating question-
 

Actually only ever owned 1 toyota, my current one that I bought about a yr ago. 2021 Tacoma.

But been under the hood since I could stand on a step ladder to help my dad. Been my career for over 20 yrs. I see ever brand, make, model out there. Working on a 86 El Camino atm.

Numbers, toyotas are no more prone to it. One may see them more often because the owners run them hot, especially if your located in the south west. But still comes down to owner stupidty. Head gaskets blowing that involve overheating are pretty much nill for them blowing and causing the issue unless external seepage caused it to go low. They are a result of the problem, not the cause. Few engines out there have issues where headgaskets are shit (actually more interface and alloy issues like old Northstar engines).

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Re: Full size Toyota owners- Overheating question-
 

1 of my subaru has 300k on it and just poped the gaskets because the radiator cap failed

still has the factory hash marks in the cylinders too so if

Re: Full size Toyota owners- Overheating question-
 

Alright... You guys have given me enough great info for me to feel better about how I need to move forward with this one. I'll decide today if I want to comp-test this engine and evaluate it's condition. I'll check the radiator level again and check for bubbles after getting it up to temp. Although I won't have much time as once it hits op-temp it'll head for the red line QUICKLY after that... like within a minute it'll go from normal temps to HOT. I'll al;so look into the suggestions like checking for milky fluid, belt tension, etc. I won't be able to drive it a fair bit though cause after idling for maybe all of 10 minutes, it has to be shut off. Same on the thermostat... I don't want to replace it unless I'm doing the water pump at the same time.

Okay... Thanks again guys for taking the time to throw your input into this one. Y'all have been a great deal of help.