CamYZ125

Ok guys (and gals!), it's actually my brother's 91 4runner 4x4 3.0l AT that is having problems. It has been overheating recently. In order to fix this, we have gone throught quite a few things. First we went to flush the system and replace the thermostat. Turns out the previous owner actually gutted the tstat so that it would be a complete flow-through... obviously to hide an overheating problem. Flushed the system and found quite a bit of junk. Decided to replace the radiator so as to ensure no clogs. Still overheats. Thought it could be the water pump- just had that replaced... still overheats!!

It will overheat quicker with a functional tstat in it, but still overheats with the original gutted one in there too...

I'm kinda out of ideas here! No oil in the coolant, no coolant in the oil... new waterpump and radiator..

Anyone got any ideas?? Thanks in advance...

tc

Fan working?

Air bubbles trapped in the cooling system?

Radiator cap holding pressure?

Good coolant/water ratio?

terryjmatthew

Weren't fan clutches bad about going out on 2ND Gens?

** Seems like I remember replacing mine on my 94 **

terryjmatthew

Try to turn the fan manually w/ the engine at operating temp (With engine off obviously!)

If it is working properly, it should be hard to turn. If there is no resistance- that might be your problem.

tc

Yeah, there's the clutch problem, also the bearing in the bracket on the 3.0. There see to have been a lot of posts about fan problems recently...

NOTE: if is the bracket, you might want to look at changing the timing belt while you're at it - you're halfway there by the time you get that bracket off...

terryjmatthew

Remembering back on it, seems like that part cost an arm-and-a-leg!(For what it is)
Something to the tune of $200-$300.00?

tc

Crazy expensive from the stealer (those prices are in the ballpark IIRC), but are available on ebay (new) and other sources for like $70

Epic Ed

Holy smokes, have I been in your shoes a lot. I have a long, rich history of over-heating issues with my damn 3.0. A few questions first:

- Have you had any head gasket work done recently? If so, it is famously easy to get the gaskets on backwards and accidently plug the holes for water flow.

- Does it heat up immediately? As soon as the vehicle gets warm enough to go to the normal temp, does it go all the way to hot? If so thencheck the water flow from the radiator -- both upper and lower radiator hoses. One may be collapsing and impeeding water flow.

The fan and fan cluth are good areas to examine, but you're more likely to notice this after driving around for a while and getting stuck in traffic or in some situation where air moving freely through the engine compartment isn't enough to keep it cool (ie., long uphill stretches).

From what you've indicated it sounds like it heats up pretty quick. I'm wondering if it goes all the way to the red (if you'd let it) regardless of driving circumstances? Or if it starts creeping toward hot and the temp varies with how you are driving? For example, if its over heating with the A/C on, but cools down if it's not on?

Ed

MorphiasX

I dont think the bearing in the fan pulley bracket would cause it to overheat. I am currently in the process of changing the fan pulley bracket on my truck (the truck is chillin in the garage waiting for the part). My truck didnt overheat at all with this problem though, the pulley was just loose, and the fan jumped around causing a popcorn-like sound, bringing my attention to it.

Have you checked the oil level? I had overheating problems when my PCV valve went out, and allowed all of my oil to get burned over a weekend of wheeling, causing me to overheat on the trip home.

CamYZ125

First of all, thanks for all of the replies so quickly! I really appreciate it.

Just talked to my brother to get more info on how it's overheating, and here's what he had to say:

With a functional thermostat in, it will idle fine without overheating (not sure for how long tho, no one has let it idle for more than 5-10 min). However, as soon as it starts to be driven, the temp will rise to the red, and it will shut down... steam and all.

With no thermostat in, it will take a little while to warm up (obviously), and for the most part if driven at speed, it will remain fine. However, if the vehicle comes to a stop, the temp will then begin to rise. I guess there's an overheat protection built into the computer?? Because according to my brother, it will then begin to change the idle, and actually want to just stall itself out. Also, he mentioned that sometimes when driving with no thermostat in, the temp will rise up towards the red, and then all of the sudden shoot back down into the normal range..

Now, what's been replaced thus far: Radiator, radiator cap, water pump, timing belt, fan clutch, and attemped new tstat.

The previous owner's claimed to have replaced the head gasket, and we were thinking that it could have been put on wrong and is blocking the water jackets too..

However, if that's the case, then it's interesting to me that the temp will rise up and then suddenly drop back down when there's no tstat in it.

Any more thoughts?

Epic Ed

Wow, that's a weird one. I'd say put the working tstat in and diagnose from there. Ultimately, you want it to not over heat with all good working parts so i'd replace the stuff you know doesn't function as designed, and address the resulting symptoms.

Also, if this engine has gone to the red already there a very good chance the head gasket is already blown. Mine blew one time and it didn't even reach the red. The blocked water jacket scenario doesn't quite fit if the temp drops back down after approaching the red, but combined with the fact the it has gone to the red at least once, I'd pull the heads and check stuff out.

Ed

suprathepeg

Hmm othere then a plugged hose somewhere I'd be willing to bet its nothing to do with the cooling system. Sounds like its not flowing enough coolant through the system and there is a block somewhere.

4runnermt

hows the heater working? Maybe a plugged heater core? Just an idea....

CamYZ125

Heater works good. I just learned that after they replaced the fan clutch, it seems to be holding temp good without the thermostat in, even at idle. However, with it in, it still over heats. I've read on here about a dual valve tstat, one that could perhaps help prevent air blockage at the tstat? Do you guys think that would be worth looking into?

Epic Ed

It should run normal with a normal tstat under normal driving conditions. If looking to prevent a problem that only happens in your vehicle under extreme driving conditions, then you can look into extra cooling fans, 2-stage thermostats, and a new radiator core.

Ed

93X-Cab Mon

Greetings Mon!! I was experiencing an overheating problem with the normal temp on the surface streets however, on the freeway, it'll climb up near the red, wiggle abit, then drop down to normal temp. Scary!! 1) replaced the t-stat, no improvement. 2) replaced fan clutch, no improvement. 3) replaced radiator with new and drilled an 1/8" dia. hole in face of t-stat. Success!! Thank you everyone who contributes to this forum, it does help very much!!

Sea-Yaaaaa!!

lemonpeppertuna

I'm experiencing the same situation, fine city driving, but gets REAL high on the freeway, esp. uphill. do you think that the same solution would work for a 22re? or does anyone have any other suggestions?
thanks, guys.
-josh

Tempy T4R

Im having the same problem. Just replaced the t-stat - there was a gutted tstat in there before.

After replacing it when the truck warmed up the idle died down to 400rpm or so. I pushed the idle back up, and it maintains good idle and good mid-range temp. at idle. As soon as I start to drive it, the temp goes up to almost the red but not quite, soon as I put it in neutral the needle will fall back down.

Brand new T-stat, it ran fine before with the gutted one, but woulnd't reach full temperature making it not shift into OD>....any ideas? Any help is appreciated

SCYOTA

I would think that the HG may be going. Your needle climbs up to red and then drops back to normal. Will it keep doing that? That is a sign of air in your cooling system. The pump will stop moving coolant. Then your coolant temp starts to heat up. Once the pump starts moving the coolant again the your temp will drop back to normal. Have you tried to burp the system? Maybe you just have some air trapped in there from changing the t-stat and water pump. My bet would be that the combustion is blowing by the head gasket into the cooling system.

ozziesironmanoffroad

check the thermostat to see if its opening properly. when i replaced mine, it would come close to overheating, but id turn it off b4 it could. checked the thermostat, put it in boiling water, didnt work. took 3 thermostats to get one that worked. (from the stealer). sometimes you just get faulty tstats. that may be your problem. to find out if your head gasket is going, do a compression and leak down test.