Hey guys- looking for some advice.
I've had several mechanics look at this and not be able to help much.

1998 4 runner sr5 194k 4wd v6

I have an overheating issue that is driving me crazy. I've had the truck for 5 years and it started doing this about 2 years back. I've changed the following since I've owned the truck- new koyo radiator- also added B&M external trans cooler, coil packs, plugs wires, thermostat, fan clutch, new exhaust from the manifold back, radiator cap (twice-OEM from toyota), top/bottom radiator hoses. I've had it compression tested and block tested - good compression and passed every test. Timing belt/ water pump done at 150k.

I am from NJ and recently relocated to AZ in November- this is part of why the problem is concerning as we approach 110 degree weather in the summer. 1stly- this is not an issue that has happened to me very often-for the most part I've only seen the truck get hot in situations like off roading up steep terrain, long steep sections of highway, and days above 85 degrees with the A/C on. In these situations thus far, I've been able to blast the heat and have the needle drop down to normal. Now- that I'm in AZ- I don't think blasting the heat is going to be sustainable. I know how terrible overheating is for an engine so I always keep an eye on the gauge and take immediate action to not run it hot.

I drove this truck from NJ to AZ in 43 hours with only a small break in St. Louis- the truck did not start to get hot once!
Just today, I was about an hour into a drive from Scottsdale to Lake Roosevelt and in the mountains I saw the needle heading towards the red and I blasted the heat and was able to carry on during my trip.
I dirtbike and camp often and I need to be able to depend on the truck to get me out into the mountains- I'm almost at the point where I'm ready to give up on this truck for a newer model.

Curious what advice surfaces here in terms of diagnosing/ fixing this.
That said- also curious what people think about a band aide style fix- for instance, could I throw in a high performance radiator or something of that nature? I know these trucks shouldn't run hot but the fact that putting the heat on helps so much leads me to believe maybe a better radiator might give me the extra cooling I need.

 

If your a bike guy like i am, I run water wetter or engine ice in all of my race bikes. I also add a half gallon to each of my vehicles.

I have also used a product called slick 50 in the past. I don't know if they still sell it. My 86 ran so cool for two years that I couldn't even get heat out of the vents

 

Are you sure your gauge is working properly.
Have you hooked a scanner or bluetooth reader to it to check temps?

 

Thanks, it is definitely overheating- not just a gauge issue. When I pop the hood the overflow coolant tank is much higher than normal/starting to boil.
I've also bought a temp gun and the truck gets hot.

 

How's the shroud?
How sure are you that the clutch fan you got is good?
https://www.yotatech.com/forums/f199...l#post52229129

 

Shroud is good- fan clutch works well.

 

I know this is simple but I only say it because my buddy's 4runner severely overheated because of this. Make sure the front and rear of the radiator is free from any dirt which could prevent airflow and check to see if you have any brake drag at all. His temp gauge was pegged at the top just because of those small things.

 

Thanks- the radiator is clean, I also checked the AC condenser and everything looks clean- no blockages that would prevent airflow.

 

Won't a clogged cat converter cause that overheating?

 

The cats are brand new- I had the entire exhaust from the manifolds back done.

 

How about trying a 160 thermostat as an experiment?

 

I'd be open to trying a 160 degree t-stat. Let me ask this- would it make sense to simply pull my t-stat- or run a gutted/open all the time t-stat?
If there is a specific 160 degree version you think would fit- please, let me know.

Thanks!

 

Also, in response to the Water Wetter suggestion- I am currently running 2 bottles of water wetter.

On a side note- I use it in my bikes too

 

Napa has a

 

It would be better to take a thermostat with a normal opening temperature like 193 or 195 degrees and drill a hole in it. Usually start with a 1/16" hole and gradually try a larger hole or more holes. If you drill too many holes or too large of a hole, your engine will never reach normal operating temperature, especially in cooler weather. You don't want to run too hot or too cold. I like to find a sweet normal operating range, which can vary with the engine/vehicle. For example 180 to 200 can be a good range for some engines. Drilling a hole in the thermostat can be helpful in the summer time in Scottsdale, not so much for N.J. in the winter time. Also a larger thermostat or a thermostat designed for a bigger engine may allow for more flow when it opens. You may find a superstat that will fit your engine.

 

I wonder if the dual-stage thermostat is applicable to O.P.'s truck.
Like this one from LC Engineering for the 22R-E...

 

Someone who is more familiar with Toyota engines may be able to comment about this, I 'd be a little hesitant to guess since the 22RE is smaller in displacement. There may be another Toyota engine with larger displacement like the 1uz with a thermostat that will physically fit and has more flow when fully open. A thermostat that is not officially listed to work with this v6 may fit fine and flow better, it is just a matter of finding the right one. I think the superstats flow better than the regular Stant stat, the superstat has a larger pellet.

 

I get this feeling that it's something very simple but it's evading all of us so far.
I'd like to recommend getting a real temperature monitoring source that gives accurate numbers....scangauge2.

http://www.ebay.com/itm/SCANGAUGE-II...IAAOSw~gRVpckM


Plugs into your obd2 port and monitors water temps. You will be amazed at how your oem gauge is fooling you....
how when the scangauge shows 220 degrees and your oem gauge says everything is perfectly normal.

And if you have an auto you can probably monitor the tranny fluid temps with the correct pid code which is searchable on the forums.
I monitor my tranny fluid temps on my 01 Taco just fine

Also, agree on removing the t-stat all together and see if it still overheats....would tell you if you had a sticking t-stat or one that was limiting water flow for some reason.
Would take a long time to warm up I suspect. But being summer is almost here in AZ means that your engine will be "warmed up" all the time.

 

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.

 

If you want to experiment with drilling small holes, this thermostat looks like a good bet. It is the only warmer stat I found listed for a 3.4 1998 4Runner. It is 192 F stat. If nothing else you could end up with a stat that works well just for summer time use or a stat to use for flushing the cooling system. You will be surprised how much difference drilling a small hole or holes will make.