runs hot on the highway

[snap-on]

I have no real temp gauge in my truck yet :( (got one in the 4runner)

some quick history, back in 2001? the second HG blew on my 3vze. At the time i had to have my truck for a reliable DD so i bit the bullet and had a Jasper dropped in. Its bored .30 over as part of there rebuild. For the year before the HG blew the temp ran dead nuts center gauge, never moved.... The 4runner the temp guage runs dead nuts center no matter what (dispite 40 deg changes in the real temp gauge i have plumbed in)

Ever sence the Jasper install its run about a full needles past center ONLY on the interstate.

I can sit at idle all day long or crawling along a trail with the AC blasting away and never break the middle of the gauge. Jump on the intersate and try doing 75 and i start riseing quickly.

If i turn the heat on full i can manage to get it to drop back to "normal" but recently it seems to be getting worse.

Popular thought is fan clutch is dieing a slow death..... you concer?

[MTL_4runner]

Popular thought is fan clutch is dieing a slow death..... you concur?


No, if it was the fan clutch it would be exactly the reverse (overheat at idle, fine on the highway).

What new parts were put on the rebuilt engine when you did it? waterpump? radiator? coolant level ok?
My guess right now is that it's one of those things causing your issue.

[snap-on]

ummmmm water pump was new.... radiator was replaced by me some time ago (cant remember if it was before or after the new motor.

coolant level is fine ive checked and rechecked it many times thinking that was my issue. Disinclined to think its the water pump as ive got good heat and you would think it would manifest its self as being a problem idle also.

The thought on the fan clutch was as the speed increases on the interstate, the wind pushing against the fan makes it slow down (ie its not locking up hard) i can run 60 all day long at mid temp 65 is one needle over, 70 is 2.. 75 is 3/4 + warm on the gauge at which point i start freeking out and either slow down and or flip on full heat.

towing or not, loaded or not, makes no diffrence.

[MTL_4runner]

Hmmmmm, so everything is more or less new now.

Did you install the HG's or did a shop do it? I know on the 3.0L there is a way to put the headgaskets on backwards that will block coolant passages and also cause a similar issue to what you are talking about. I would change the thermostat again just because it's cheap and easy to eliminate (be sure to install with jiggle valve at 12 o'clock to remove air from the system), but the issue may be more involved than I initially thought. Also note how fast the coolant comes out, if it's a trickle and continues to run for a little while, you'll know for sure my guess below is right.

I hate to say it, but it is possible the HG's are on backwards. The fact that the temp is just above halfway at idle (the temp on a motor that is running well should always be less than halfway on the temp gauge) and then climbs steadily as you work the engine harder at speed and all this came right after your engine work was done, really seals the deal for me. This is a common problem that's easy to make and even experienced mechanics sometimes make the mistake. I've heard of them being swapped, having 2 left or 2 right side gaskets, you name it, but it all sounds all too familair to what you're describing.

If you have a borescope you can pull the thermostat and look up into the block to verify if the cooling passage is clear. You can also use a coathanger wire to check but it can be harder since you don't have visual confirmation of what you're running into.Either method only confirms the accidental swapping or if you installed 2 left side gaskets (if you have 2 right side gaskets you'll and only one head is overheating, then you'd need to pull the heads to verify).

[snap-on]

guys note the dates.... ive run the jasper (built by jasper) for 6? years now...it has over a 100K on it and runs strong.

this is a cooling issue ONLY when traveling on the interstate. Every possible concievalbe combination of driving condtions ive put it through. the only time the temp creeps is cruseing on the interstate.

[MTL_4runner]

I saw the timeline but it still doesn't sit right with me that your gauges were solidly at the halfway point before the engine was put in, then after the rebuilt engine went it, the gauges showed the engine ran hotter than before and that it crept up with speed.

You can test the fan clutch like this:
http://www.barneymc.com/toy_root/techneek/fan_clch.htm

If it tests bad you could replace (go to the dealer or get a used OEM one, the aftermarket ones are usually NG) or rebuild the fan clutch and see if that was the ticket ( http://www.4runnerforo.com/phpBB2es/viewtopic.php?t=89 translate using babelfish). Most of the time highway speeds provide more airflow than the fan could so the fact that the fan isn't engaging usually would show up while idling for long periods of time with the AC cranked or rock crawling offroad (ie where the engine gets little air movement from the speed of the vehicle). You could also go ahead and do the Taurus mod since it's probably about the same cost or less than buying a new OEM clutch from the dealer.

[dcg9381]

I can't see the avaitar you've got very well, but do you have a winch in front of the radiator?

[Piett]

Have you gotten a build-up of mud or other crud obstructing air flow through the lower part of your radiator? At low speeds the fans moves enough through the top but at higher speeds you need the cooling of the entire radiator which might be slightly obstructed.

[Piett]

Snap-on,
When did you add the tranny-cooler?

[snap-on]

no tranny cooler on my 5speed truck... added the tranny cooler to the 4runner with an A340H after i did the rebuild on it.... it runs great...

ya the avitar pic sucks.... if i can get someone to tell me how not to get it to resize it, it would look right.

and yes the ARB bar does block some of the radiator...

[blink]

Did you try replacing the radiator cap or the thermostat? Might be something as simple as that.

[YotaJunky]

Have you tried running it without the thermostat? If it still overheats, I'm guessing that you've got a circulation problem somewhere in your cooling system.