the1998sr5

It seems that someone had a similar problem on t4r.org, but it is an old thread and I have not gotten any responses.

1998t4r, 170k, new cat & exhaust, new Koyo radiator last year, new radiator cap.

MY 4 runner has run above normal temp twice now at the same section of trail (stokes forest NJ). It is about a 1/4 mile section of trail with several steep sections, but nothing crazy. For reference, I could make it up in 2wd, but it would spin in a few spots (no diff lock).

This happened a month ago and my local shop said poor exhaust flow, so I got a new exhaust (820$), this did not solve the problem.

I do not let it get in the red, but it is significantly north of the normal middle spot on the guage. Coolant resivior is usually 2 inches below below full line cold, and at full line at normal temp. When the truck starts to get hot it gets way full-perhaps 4 inches above the line and it gurgles when I kill the engine.

I have tested the fan using the folded magazine method and it seems to grab well ( I cant stop it) and the oil and trans fluid look normal. I did ask my local shop about the color of the coolant because I was concerned about milkshake (even though I have a new koyo). When I bought the truck it had red, but they put green in the new radiator. In the resivior it looks green on top and red on the bottom?? Shop said it is likely some of the old coolant, and it does not look like a trans/ antifreeze mix.

No check engine lights, no overheating on the rest of the trail, no overheating on the 70 mile drive home, or city driving. Just uphill, offroad. Unfortunately- this is a problem for me because I like to hit the trails. I do not beat on this truck - hardly ever gets above 3k rpm and I do not bog it either.

Any ideas on where I should start?

YotaWoRx

Remove the thermostat and test it with a kitchen thermometer in a pot of water on the stove. It should open fully at above the temperature stamped on the thermostat. Also perform a cylinder leak down test to make sure the head gaskets are ok.

JasonYota

iTrader: (1)

Have you verified the temp with a inferred temp gun? It's good to know what it's doing before taking it apart and throwing new parts at it.

the1998sr5

I have not verified the temp with a temp gun.
Where should I take the temp reading?
I'll likely need to field test this on the trail, as that is the only time I have seen it get above normal.

Does anyone else's 3.4L ever deviate from the normal operating temp under load?


I did have it compression tested about 6 months ago (before this happened), and it was good (I forget the exact PSI per cylinder, but none were low)- I guess I could check this once more.

Would a faulty thermostat only cause an issue in this unique situation?
I'd also like to note that I was up this trail about one year ago and it did not get hot- to further verify that something is definitely awry.

JasonYota

iTrader: (1)

If get readings at the upper hose coming out of the motor on the metal part. Thermo housing and upper and lower hose readings. Cylinder head temp, exhaust manifold temp, just all over.
Also if you have access to an OBD2 reader you can see the actual coolant temp through the ECU. There is one sensor that shows that reading and one sensor that goes to the gauge on the dash.

the1998sr5

What temp would you say is Danger Zone?

wyoming9

iTrader: (1)

Being it only does it on the trail and you have a auto Tranny I would bet your not getting enough air through the radiator .

Could be something like your fan clutch you said you checked.

Could just be the rpm is to slow to pull enough air as your crawling up the hill. Do you have any idea of the rpm`s your at. Low range Low gear perhaps??

I run the all metal 3row radiator on both my 3.4 engines.

I don`t do low rpm loaded heavy unless it is sitting in traffic because of stunt driver mistakes or road destruction and all mine are manual transmission. I have never noticed any cooling problems

Stuck thermostat would be pretty much all the time .As cheap as the Stant products have become I went back to Toyota Thermostats.

The offer is always open !!

the1998sr5

I'm glad you mentioned low gear vs high gear (4wd). That thought crossed my mind as well. Perhaps I should be in 4lo right now? Unfortunately I babied it up the same section in lo and I got the same result that I did in hi.

The RPM range is 1500-2000, perhaps crossing the 2 here and there on the obstacles.

I'm considering doing a few things at once, but I am not 100% sure on this yet.
I'm thinking:
-external trans cooler, trans oil change (I was on the fence about this because the guy I bought it from did not know when it was last changed)
-new tstat, new fan clutch
-coolant system flush, or new radiator if I get a good paycheck.

It's a catch 22, because I don't mind spending this money if I am going to run cool afterwards, but I'd be in a tough spot if I still have the same problem.

wyoming9

iTrader: (1)

Just what are the specs on that radiator?? It was new correct??It is not filled with mud or bugs

Not being a auto trans person I don`t know if the transmission could be dumping enough heat into the cooler to cause lack of engine cooling.

A stand alone cooler never hurts.

All the hoses in good shape or have been replaced not long ago like with the new radiator?? All mine are new

a infrared temp gun to see if you have blockages in the radiator or a scanner to read real time engine temps

Although that might be a pain bouncing along in the woods without a copilot to hold it.

the1998sr5

My radiator is a Koyo 1998a, I believe. It was highly recommended on this forum.

My Auto fluid is dirty, not mud filthy or burnt, but its far from pristine
Could that be causing the trans to run hot enough to heat the coolant in the radiator? It shifts fine.

Another idea is the AC condenser, could it be that that is dirty and blocking the radiator? I took a look at it and it is dirty, but not caked with mud or anything crazy.

I am going to pick up a temp gun and a scanner. Since no mechanic is going to come up the trail with me I am likely going to figure this out on my own (and with the help of the forum!)

Texas_Ace

It makes sense that it would only have this issue off-road going up hill, there is virtually no airflow over the rad and a lot of heat being pumped into the coolant by the engine.

Highly doubtful that the trans is causing the issue although getting an external cooler is still a VERY good idea for the trans life.

Clogged airflow over the radiator is something to check for sure if you off road a lot.

Also you have the fan shroud on right?

If all that checks out then start simple, do a complete radiator system flush. Get the heavy duty flush and clean that sucker out. Rinse the system a few times after this with water to clean everything out.

Then refill with coolant and toss in a bottle of water wetter.

See how things go after that.

If you still have issues then start messing with the expensive stuff.

the1998sr5

Thanks for the response Texas, I do have the fan shroud on.

I'm all for starting with the cheap stuff first! When you say heavy duty flush, are you talking about bringing it to a shop and having it flushed with the machine.
Any ideas on what to ask when qualifying that they are going to use the right process?

Texas_Ace

No, just go to the parts store and get the heavy duty flush bottle. They generally have the basic flush and then the "heavy duty" (they are basically the same thing in reality, the HD stuff simply uses more of it and the instructions are different having you leaving it in the system longer).

Takes time as you have to get the system hot and then flush it out a few times as well but you can do a perfectly fine job in the driveway.