3.4L V6 Oil Cooler O-Rings Failing: Proactive Replacement Recommended

I noticed a couple of recent threads where 3.4L V6 Taco owners were experiencing oil leaking from their oil cooler. So while my '97 Taco is on the jackstands for periodic MTX and upgrades, I ordered the O-Ring & gasket from McGeorge/Ourisman. The RWD V6 Taco has room to work on this from the bottom. But access to the oil cooler on the 4WD V6 Taco thru the rear of the L wheel well is limited. If you have someone to help, especially someone with smaller hands, their assistance would be of great value in correctly reinstalling the oil cooler. The original O-Ring on my oil cooler was completely hardened & stuck to the block. It was removed with long needle nose pliers and broke off in several pieces (below). There was absolutely no elasticity left in it. Just finished up and it was a royal PITA, mostly due to problems getting my XXL paws in thru the L wheel well to reattach the oil cooler to the engine while keeping the O-Ring in the correct position on the oil cooler. The new O-Ring kept falling out of position, so I put 4 extremely small dabs of RTV in the groove of the oil cooler to hold it in place. I let the RTV get tacky before reinstalling the oil cooler @ 43ft./lbs., which worked out well. Bottom line: The hardened original O-Ring on my '97 V6 Taco was long overdue for replacement, prone to failure at any time. Based on the extremely poor condition of the O-ring in my '97 V6 Taco, I would recommend that all 1st Gen V6 owners replace their original Oil Cooler O-Ring & gasket at their earliest opportunity if they have not already done so. Winter is upon us and that is when pressurized O-Rings/seals have routinely failed on me due to all the thermal expansion-contraction cycles coupled with high oil pressure from cold-starts. .02

EDIT: Some people with 3.4L V6 2WD Tacos have been replacing the O-Ring and gasket without draining the coolant and removing the hoses to the oil cooler. I am not sure that I could fit my hands in there to do it correctly on my 4WD Taco, but it may be an option for some of you. My oil cooler was far too filthy anyway, so had to be removed/cleaned before bolting it back on with a new O-Ring & gasket.

Original '97 O-Ring & Gasket condition was extremely poor:


'97 3.4L V6 Taco Oil Cooler Diagram with O-Ring & Gasket P/N: Check your VIN to verify P/Ns for your V6 Taco.

FSM EG189 & EG190:


New O-Ring attached to cleaned Oil Cooler with (4) extremely small dabs of Ultra Black RTV:

 

good info!
how big is tht union bolt? 19mm?

 

The bolt is 24mm, but I used a short 15/16" SAE socket with long 3/8" wobble extension which worked fine. It is pretty tight in there, at least for me (below).

Access point on '97 3.4L V6 4WD Taco:

 

oh man 24mm!!

 

24mm is quite common on these vehicles.. Rear diff drain and fill, xfer case drain and fill, etc... Gotta have a good 24mm 6 sided socket on hand.

 

You have to work around that hard brake line on the left or move it out of the way then bleed the brakes when you finish with the oil cooler. My 24mm 6 point impact socket was just too long to work well on this job, angle was getting too extreme for the wobble extension. A short socket kept the angle more workable especially for using the torque wrench. That short 15/16" SAE socket has worked all over this '97 Taco for over a quarter century, has not failed me yet.

 

The rear diff fill plug uses a 24mm

however a 15/16 had a tighter more snug feel..
less chance of rounded it....

 

Good to know. Any change a 24mm crows foot line wrench would be the right answer?

 

The problem is those old bolts with large diameter are notorious for seizing/bonding to surface.......gives even a 6 sided socket a run for its money.....

thats the reason they tell you to pull the fill plug first....before even messing with the drain one....




The really pia one is the front diff one.....the one with the allen key.....

I would get rid of that and put a rear diff 24mm one in its place...
pray it will even break loose in the first place...

 

I think you're a little OT here. I was merely mentioning that 24mm is a common size for these trucks. Didn't mean to drag what started out as a relatively informative thread into a shit show.

 

Yes. My short 15/16" SAE socket does feel tighter on drain plugs, etc. than the longer 24mm impact socket & has always worked fine for me on this Taco. The longer 24mm impact socket mostly gets used with one of the impact wrenches.

 

I appreciate this write-up. I discovered a leak on mine today.