Hopin some of you 3.0 liter guys can help me out with this one. To make a long story short, my buddies truck had a dead cylinder so after some investigation we determined one of the exhaust valves was gone. Anyways, put the new heads on which was a job to say the least. The heads were remans from National Cylinder Head or something like that from Kentucky. Got it all back together which was just like taking it apart only worse haha. The truck has a new radiator which was installed about 2 months before the head swap.

Once we got it all together fired it up and a few little button up details we missed like a vacuum leak or two. Got that all straight and was setting the timing and all that. I noticed that the temp gauge was creeping up some. Well the truck got a lil hotter than I like so we shut it down. Now it won't hardly over heat idling but it will driving down the road or revving it between 1500-2500 rpms. At 3500 and above it will cool back off to normal operating temp. Groundspeed seems irrelevant but engine speed seems to matter greatly.

List of parts replaced since this issue started:

New thermostat
New fan clutch
Radiator only two months old


I just put the new fan clutch on it today. Really thought that was gonna take care of it because the last time we drove the truck, I got it a lil hot and we stopped, stuck a screwdriver on the fan and brought it to a halt with no problem. Well the new fan clutch didn't fix it. I've tried burping all the air out of the system. One thing I did notice after running it with the new fan clutch was that the top radiator hose and top tank were scalding hot but the bottom hose and tank were only lukewarm. I could hold my hand on them for an extended period of time with no new blisters on my hand. The only explanation for this I can come up tih is that coolant is not making the full circle thru the engine. My question is why? I don't much about a 3.0 liter but they have alot of small coolant lines and various other contraptions on the intake around the top of the motor. If anybody has any ideas I'd greatly appreciate it. Maybe I'm missing something. I'm waiting on the truck to cool down and I'm goin to go stick a gutted thermostat in it and see if the problem persists.

 

Just got done putting the gutted thermostat in and now the SOB runs normal operating temp no matter what you do to it. I have to say I'm more confused now than when I started. We have tried atleast two different t-stats plus the gutted one and the only one it likes is the gutted one. I don't like that as a permanent solution though.

 

How's you water pump?

 

I was having a similar problem. I bought my 90 4runner from a guy who just rebuilt the motor, he said he was running it without a thermostat so I thought that was weird. I put a new thermostat in and it overheated within about 5-10 minutes. After changing the radiator, fan clutch and testing the thermostat (to make sure it was opening) we determined that it was a bad head gasket....Ripped the motor apart and it turns out he put the Left gasket on the right side and the right gasket on the left side. This caused a coolant hole to be covered on the driver side. Put on new Toyota gaskets, etc., and the 4runner runs great now.

I hope this isn't your problem but it sounds like it is.

Good luck!

 

Yeah that's kind of the point I'm getting to with it. I really hope its not. Unfortunately I was at work when he put both the heads on it so idk for sure. We looked at the old headgaskets and it looks like it would be hard to confuse them but who knows. I told him to buy a 22R haha. Anyways, it runs great and its driveable with the gutted thermostat so the hell with it. Its got 240,000 thousand miles on it and he only paid a thousand bucks for it like 3 or 4 years ago so he's definitely got his monies worth out of it. Its just strange that it will do ok with no themostat if a coolant port is blocked. Changing the thermostat isn't goin to unblock it unfortunately....wish it could be that easy but oh well. The head gaskets are a right big project on that truck.

 

If you look at the back of the motor on the passenger side. You can see if there is excessive material sticking out. if there is they are backwards.

 

Did you drill out a small hole in any of your thermostats? that little brass plunger type thing in the rim lets some fluid bypass when the stat is closed but isnt enough IMHO. I drilled mine out to about a 3/16 inch hole. This was a tip passed on to me by my machine shop that did my heads. The guy that runs it does alot of toyota's and really knows his stuff. also when you burp the system take off one of the hoses at the back of the block. the one for the heater is what I use.

I then take off the upper radiator hose and hold it up and start pouring it in. worked good for me that way. I'd burped it several times after my rebuild and this still got air to come out.

GOOD LUCK!

 

That's where my 4Runner is. Thermostat = overheat. No thermostat just fine. The only downside is that it takes longer to warm up to operating temp, and with an automatic it won't shift into OD until it does.

 

Did you "Burp" the cooling system. If you raise the front of the truck and fill system thru the upper radiator hose you usually got all the air out of the system.

 

The is also the "backward-cut" gasket phenomenon. I don't know if that would cause it, but it's disconcerting.

 

I tried burping all the air several times with no luck. I haven't noticed the gasket sticking out of the back to far and I think that would've caught my eye but ill look again. The new thermostat he bought didn't have a weephole in it so that may be causing the problem. The weird thing was the difference in temp between the top and bottom tanks and hoses on the radiator with the thermostat in it. Now they run about the same temp. Drove it 120 miles with no issues on Sunday. Gonna get a new thermostat from Toyota this week and try that. Other than that screw it, hopefully he will blow it up so we can swap in a 3.4 or a 4bt Cummins. That 3.0 ain't worth the aluminum they used to build it in my opinion. The truck has 240,000 on it so we'll run it til it won't go no more. Thanks for the help and opinions guys.

 

The 4BT is a heavy engine...I'm not sure how the chassis would like it.

 

I've had this same problem on my '91 for 2 years. Back to the gutted-thermostat again. I did the timing-belt and I thought I'd found the problem with the timing-belt and water pump were very oily due to bad front main seal (why would the PO replace the cam-seals and not the nasty, leaky front main it's way easier ??) After cleaning everything and putting in a new thermostat with a me-drilled 3/16" hole at 12-oclock everthing was fine, for about 10 minutes then 'HOT' !!

I also did the 'fill through top-radiator hose trick' on this forum even tried it running (who's bright idea was this the top hose is the motor-OUTLET so the pump pumps all the water all over your belts and then the fan blows it into your face !) but nothing has worked. Head Gaskets are next, then I mays sell 'er not sure yet...

Perhaps someone could recommend a very strong engine-flush as I have the green anti-freeze and rust. I read on here that red is the one you need now I need to lose the block-rust...

 

I've done this about 6 times and it is not working for me... I may try the one with the heater-hose at the back of the motor being dis-connected next.. This sucks...

 

Still having no issues on the gutted thermostat so screw it...I think he's gonna let it ride. I might try a dual stage thermostat from Toyota but other than that I am baffled.

 

My own rig is doing that as well. No misses, no oil in coolant, no coolant in oil. The only sign of a head-gasket problem at all is the test where you put the new radiator cap on, then put the overflow tube into a jar of water and I can see regular small bubbles coming up, that tells me I have a minor leak. The way I see it, the bubbles go to the thermostat-bulb and hang-up (even with a 3/16" hole) and it closes after about 10 minutes or so of running around.. Mine is gutted now also, I'm thinking hard about selling 'er....

 

whats that saying if you fix it long enough you will break it id just enjoy it maybe its fond of the old thermo