Having a Tundra in my auto collection, a few folks over at tundrasolutions with the 4.7 V8, who have never replaced the tensioner, but have high miles (200,000 +) have had their timing belts break due to the failure of the tensioner. And since that engine is an interference one, when the TB snaps, things break.

So it looks to be mechanically prohibative to replace the tensioner every TB change then unless one is putting high miles on their 3.4 yearly. I don't see why not to. Qyota, if you tackle this, take pics.

 

On the trip home yesterday, I never got it all the way up to 215. I did see 205-208 for a while though. What I noticed was that even with engine rpm up (say 3k for example) and going uphill....my coolant temp wouldn't really climb until I turned the O/D off. Strange huh.

As soon as I clicked the O/D off, my trans temp would start falling, and my coolant temp would start rising. My trans would settle into about 170 range, and the coolant would climb from 190 up to about 208. Which seems strange, because the RPM and vehicle speed were the same....I'd click the O/D off when I was traveling at a speed that the engine could still stay in high gear and be running 3.5K RPM.

So:

RPM 3.5K with O/D on = 190 coolant temp, 190 ATF temp

RPM 3.5K with O/D off = 208 coolant temp, 170 ATF temp

 

This one has me perplexed....

I am going to drive the 4 runner into work tomorrow with O/D off just to see.
I'll report from there if anything is noteworthy.

I towed a 3200lb boat/trailer/the works last summer with O/D off, A/C blasting, and I never saw the coolant temp rise past 195 on the freeway as well as at the moronic stop and go public boat landing traffic.....

 

I can't think of much to say about that either.

 

Mine behaves much the same way, quicksilvr. There is no rhyme or reason to the water temp. I'll be traveling on a flat road in O/D with the cruise set at 55mph, on a 20-degree day, and the temp will range from 202-206 with no input from me, and no more effort for the road grade/condition.

Wouldn't a failing tensioner make some noise? Same for the water pump?

It wasn't always like this. I noticed the change shortly after towing a small pop-up camper early last summer on a relatively hot day (upper 80s). Nothing go too hot, but the temp has read higher ever since then.

 

With the 25 mile commute into work here today, with O/D off and crusing at 3200 RPMs, 191-193 coolant temp at 60 degrees, except idiling in traffic where it reached 197 momentarily. A new fan clutch may be needed this year.

Quickslvr, Qyota: have either one of y'all ever tested the thermostat in the pan per Mt. Goat's pics? Kinda neat to see it open, but never perform the test of a used tstat in a pan that you or love one uses for daily cooking or there will be trouble in the house

 

Haven't tested, but will be replacing soon anyway.

 

I cruise at half of that!

 

get a electric fan if you want cooler temps.. and have it set up to a switch in the cab.. so i can be turned on when you wan it on... or you could get a secondary fan switch and just plug it some where into a coolant plug or just make a coustom setup with some pipe and and your coolant hose and some hose clamps...

heat is a killer of a engine... keep it cool with a set of electrical fans...

 

When one drives the 295 beltway in DC, it sometimes feels as if one needs to constantly keep 3200 RPMs in order to get away from the idiot drivers; in reality it was ~2200.

 

Same temps with the o/d off, maybe a couple of degrees cooler.

I'm itching to do my timing belt job. I hope I get a refund from uncle sam.

 

Nope. But I've got a bunch of stuff slated for this spring. Coolant flush with a new t-stat is on that list. I'll test the old one then.

Yesterday and today, during my normal driving (a 25 mile loop around my metro area) my coolant was 188-190 the whole time. I've never seen it close to 200 except during this recent trip to Colorado. And I also noticed that my overflow tank got emptied after this trip......pretty sure the excess heat pushed all the extra out the top. I had the overflow tank overfilled to start.

 

E-fans are nice, but there is a root cause of these vehicles running "too hot", when really they should be closer to the opening temp of the t-stat. Adding a fan is a bandaid.