99 4runner Overheating in sand washes

[KingJew_1902]

Alright guys, need some pointers.

First shake down trip for my 99 4runner this past week for Thanksgiving after 2 years of piecing it together and actually finding time for the desert again.

The rig:
3.4 V6 rebuilt 13k miles ago (or 2yrs ago)
New radiator installed same time as eng rebuild
4wd
BTF +4.5 LT kit
Custom 4 linked rear end
4.88 gearing
Metric 35’s

Camped in Ocotillo Wells off Pole line Rd
Had fun running around in the hard pack but as soon as i get into the washes it would start to overheat after a few miles running it hard. I kept it in 4Hi, trying to keep up with a can am sxs and 4 dirtbikes.

I had some some issues with battery mount allowing the battery to shift, broke a ground wire. Noticed a rough idle so I checked plug boots. 3 werent fully seated. Fixed each of these issues. After the idle issue ai split from the group and hit the hwy back to camp.

After getting back to camp i found the air intake hose that connects directly to the throttle body wasnt fully seated. Fixed that hoping it was running lean and caused the overheating.

Next day all seemed well until I started hitting the sand washes again. Then a repeat of getting hot.

I was thinking maybe a larger radiator and electric fans could help but is there other things I should look at to alleviate the OH issue?

 

[desert_steve]

How bad was it overheating? Were you reading the actual temp (OBDII port) or going off the dash?

Simple stuff 1st: Check the coolant level (is it full and topped-off/burped after the rebuild and new radiator?), rad cap (is it old? Sealing? Holding pressure?), thermostat (did you replace it during the rebuild? Did it get installed correctly?), etc.

 

[KingJew_1902]

How bad was it overheating? Were you reading the actual temp (OBDII port) or going off the dash?

Simple stuff 1st: Check the coolant level (is it full and topped-off/burped after the rebuild and new radiator?), rad cap (is it old? Sealing? Holding pressure?), thermostat (did you replace it during the rebuild? Did it get installed correctly?), etc.

So the needle went 3/4 maybe slightly higher from redline on the dash. I threw the heater on high to save it from going further into red. Needle normally sits at half way.

Coolant level was still full after checking.
Just did a head gasket and top end in Oct 2023 after oreillys thermostat failed.
Replaced the rad cap about 6 months ago.
I didnt burp the radiator, im assuming the engine shop did it.

 

[Giant Geoff]

That is standard. I air down to 19-22psi for the desert to help with traction and the chatter!

 

[cbrewer22]

does trans fluid go into radiator on those.

 

[KingJew_1902]

does trans fluid go into radiator on those.

I believe it does.

 

[84Prerunner]

Don’t do electric fans. It should have no issue staying cool if all stock stuff is working correctly.
Need to get an actual number on how hot it’s getting, anything under 225 is nothing to worry about.
I run 25% red coolant, 75% water, stock radiator and fan setup. Can bounce off the rev limiter all day in the sand without issue.

 

[96f-u250]

Lets see a pic of the front bumper and skid plate and whats blocking your radiator.

 

[KingJew_1902]

Lets see a pic of the front bumper and skid plate and whats blocking your radiator.

 

[Dezert4Runner]

4hi offroad tends to make the auto trans in these vehicles work pretty hard, especially with large tires and soft sand. The trans cooler is built into the radiator, so bypassing it with a standalone one would help with the strain on the cooling system. Also, these vehicles have known issues when the radiators get old and getting the pink milkshake from trans fluid mixing, so bypassing it helps avoid major trans failure too. Replacing the radiator like you already did makes this less of a worry of course.

Air in the cooling system, bad rad cap, failing t/stat or fan clutch could all cause overheating under the right circumstances and also not come into play under normal driving. T-stat being installed with the jiggle valve at 6 o’clock is correct and will run cooler than if it’s installed 12 o’clock. The 3 mounting bolts are triangular in orientation so you can definitely install it incorrectly if you’re not careful. Been documented with the 5vz-fe on other Toyota based forums for years. Usually around 5 degrees difference from what I recall.

Without being plugged into the obd2 seeing live data, the temps could be within tolerance and just be elevated which is normal under those conditions. I would start to get nervous over 210 myself, but the 5 speed trans and j shift t-case in my 2000 4Runner isn’t problematic under the same driving conditions. My experience with the stock (dummy) temp gauge is that once it shows it’s hotter than the allowable variance and it will just continue to climb and the vehicle is legit overheating at that point. I run a wifi version of the ELM 327 which monitors live data like a Scangauge and I hit 205 coming through Randsburg on highway 395 during a 112 degree summer day and my temp gauge still showed the needle in the typical spot in the middle of the gauge. I’m on 35’s with stock gearing so it was working pretty hard on some of those hills!

 

[FENDERFAB]

I would start by installing a stand alone trans cooler and not run it through the factory radiator.

 

[KingJew_1902]

I would start by installing a stand alone trans cooler and not run it through the factory radiator.

I think this is definitely part of my problem.
In addition to a stand alone trans cooler Im going to check my thermostats orientation, check the fan clutch and refill /burp the radiator myself.
I will also need to get an obd II reader for the individual temps

 

[cbrewer22]

I think this is definitely part of my problem.
In addition to a stand alone trans cooler Im going to check my thermostats orientation, check the fan clutch and refill /burp the radiator myself.
I will also need to get an obd II reader for the individual temps

If it’s driving fine and only overheating in the sand I would just look into the trans cooler. If it was a thermostats, fan clutch or air in the system it would do it more often.

 

[BigRonDog]

I had a very similar set up with a lot more added weight with skid plates, bumper, tire carrier, winch etc.. I never had any issues out there. As mentioned above, when running 4 wheel drive it always tended to add strain and get hotter than normal, but not over heat. My engine and trans was stock with the stock cooling system. I had lights and a winch on the bumper and still air flow wasn't an issue.

Sounds like you might have air in the system, but if this is only happening in the dirt than that is not likely. I do not have an answer for you, but I will reach out to the Toyota gods in my circle and see what they come up with.

 

[KingJew_1902]

I had a very similar set up with a lot more added weight with skid plates, bumper, tire carrier, winch etc.. I never had any issues out there. As mentioned above, when running 4 wheel drive it always tended to add strain and get hotter than normal, but not over heat. My engine and trans was stock with the stock cooling system. I had lights and a winch on the bumper and still air flow wasn't an issue.

Sounds like you might have air in the system, but if this is only happening in the dirt than that is not likely. I do not have an answer for you, but I will reach out to the Toyota gods in my circle and see what they come up with.

Unfortunately the sand caused the overheating. Hwy, street and hard pack dirt driving all seemed to be fine.

This weekend I'm going to spend some time to figure this out.

 

[Dezert4Runner]

Air in the system is really seeming like the culprit after knowing this vehicle was in the shop last month and the coolant was refilled. If you burp the system, remember to turn on the rear heat on the back of the center console, if yours came with it. Those heater lines could be holding a pocket of air.

 

[KingJew_1902]

Air in the system is really seeming like the culprit after knowing this vehicle was in the shop last month and the coolant was refilled. If you burp the system, remember to turn on the rear heat on the back of the center console, if yours came with it. Those heater lines could be holding a pocket of air.

The rear heater lines were rusted thru and I removed them. Ill give them a once over as well. Good call tho

 

[KingJew_1902]

Found the issue. My fan clutch is bad.
Im still going add a trans cooler for peace of mind

 

[84Prerunner]

Found the issue. My fan clutch is bad.
Im still going add a trans cooler for peace of mind

Needs to be a good sized cooler if you’re going to delete the stock heat exchanger in the radiator, not one of those $50 pep boys/summit coolers. Another cheaper option is to add a smallish cooler before the radiator. That way both coolers still function but takes a lot of load off the radiator.

 

[KingJew_1902]

Needs to be a good sized cooler if you’re going to delete the stock heat exchanger in the radiator, not one of those $50 pep boys/summit coolers. Another cheaper option is to add a smallish cooler before the radiator. That way both coolers still function but takes a lot of load off the radiator.

I was looking at the Derale trans cooler w/fan pn13900