ZUK

iTrader: (1)

More thoughts after re-reading your post.......everything you describe just seems to point to a water flow issue....most likely the radiator...but you say it's a new KOYO. Still points to it. If, as you say, the condensor or radiator is not blocked by mud or leaves then WIND(air flow) is not a problem on the highway....and it points to waterflow and the eye is back on the radiator. That's why removing the t-stat is a good idea for testing.


another thought....what if the lower radiator hose is collapsing when it gets warm? That would limit waterflow....

But I read in your original post that the t-stat has been replaced TWICE with oem.....and the lower rad hose also replaced(with a thick quality hose I assume).......so we are back to the radiator.

ZUK

iTrader: (1)

I'm thinking something is not quite right with that new Koyo radiator.
My 01 Taco has the 3.4L with auto.....and I replaced my oversized original radiator with a 4" shorter one designed for the 2wd models with the 4 cyl engine.
no overheating issues thanks to the info supplied by my scangauge2
see this......
https://www.yotatech.com/forums/f152...l#post52234256

the1998-sr5

Thanks for all the input so far.

I have checked the hoses when this happens and it does not appear to be a hose collapsing.
Would you guys say trying another new radiator is my best bet at this point (even though mine is new)? Other than the Koyo- are there any performance radiators that would cost a bit more but cool better?
I know the pinion bearing makes some noise- there is no play in it, but I can hear it- could this be significant?

Also- does anyone know for sure if the scanguage could monitor trans temp on a 1998?

Finally- the trans lines still run through the radiator in series with the B&M trans cooler. I have never changed the tans fluid- it is dirty, but not filthy or burnt- is it possible the trans could be hot and causing the engine to get hot?
I was afraid to change it because the guy I bought it from did not know when it was changed last- trans shifts fine today.
Would shutting the overdrive off on hills increase heat generated or decrease heat generated?

It just kind of boggles my mind that the heater solves this, I mean how much extra cooling can the heater core accomplish- I'm tempted to redirect the vents outside of the cabin

Marc

I don't think the scangauge can monitor transmission temps on anything older than 2000.

RAD4Runner

I like this temp gauge. IIRC Ronny Dahl (4wheeling western australia) uses it or similar:

75w90mantraN

Definitely change out the old trans fluid. Hot temps, hot tranny, inclines (guess is overdrive off COULD decrease temps, depends on how much rpm after), could tax the radiators workload, though that trans cooler should help. Assuming no leaks. You must be doing some serious wheeling! Anything else that can contribute to your issue? Towing? Big wheels? No engine light coming back on?

75w90mantraN

Maybe at least changing the coolant out after the long trip or if its been over 2 yrs / 24k mi (ballpark guess on recommended figures) with Toy coolant would help. Worth mentioning, but I assume you may have already done that. Haven't looked up Koyo rad. If its made in Japan, its reassuring. No blockages...ok.

These 4runners, I forget if OP said his was supercharged, are not fast hill climbers. I let the engine take its time and use lower gears. Have driven mine in desert heat, towing the Accord in 1 hr plus drives through some of the hills and mountain passes of SoCal and never overheated. Stock cooling system.

Coolant level rises when engine is operating. Never seen it boiling. Which makes me wonder the condition of the coolant, and the conditions the engine is dealing with.

Again, that trans fluid. May need a couple drain and refills over the next several months, since its still the same since purchase. And it's a good idea to go over anything else that may be due for the engine. Lot of things, if left to their own devices, can contribute to more stress on the engine. Hope this situation gets better for you. Let us know how you do.