Kind of "Mystery" Coolant leak back of engine (heat exchanger valley leak)

[Acrad]

Are you considering using the J2Hundy Gasket?

I used the gasket on my 460... so far no issues

Post in thread 'DIY Coolant Valley Leak Repair'

Feb 20, 2026

Gasket instead of FIPG for repair

Vendor: J2HundyOutfitters - https://forum.ih8mud.com/members/j2hundyoutfitters.230864/
@J2HundyOutfitters

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Discover premium off-road and overlanding gear for the Toyota Land Cruiser 200 Series and Lexus LX570 at J2Hundy Outfitters. Explore innovative products, expert advice, and custom solutions to elevate your adventures. Visit us at J2Hundy.com!

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1URFE/4.6 Valley Guard Seal

🛡️ 1URFE / 4.6 Valley Guard Seal For Lexus GX460 & LS460End the Leak. Reclaim Confidence. Drive On. Your Lexus 4.6L V8 was built for refinement, not regret — yet hidden deep in its engine valley lurks a design flaw that can sabotage it all. The factory heat exchanger cover sits atop two...

j2hundy.com

#CoolantValley #J2Hundy #Coolant #Valley #Gasket

• Acrad

Post in thread 'J2Hundy Valley Plate Leak Guard Seal'

Feb 24, 2025

If any of you know me… “knowledge without experience, is just, information.” So let’s give it a shot and see what happens. Here’s about the 30th coolant heat exchanger re-seal I’ve done. I like doing this job, I find it pretty easy and satisfying. I even plan to offer this service as a mobile job, when I’m stateside.

Background: this particular 3UR came to me after having the coolant heat exchanger plate re-sealed with 1282b about 80k miles ago. I know the Toyota master mechanic that did the job. I highly doubt he did a poor job. So here we are, customer wants...

• Taco2Cruiser

• 

 

[electro992]

Are you considering using the J2Hundy Gasket?

I used the gasket on my 460... so far no issues

I did see that and was a little tempted. In general I try to stick to OEM parts and procedures. My thought (right or wrong) is if a gasket was a better solution, Mr. T would have put one there from the start.

 

[Acrad]

I normally do as well…but overall feel OEM setup ..and IMO… is a weak design flaw…a few too many redo’s reported on the 460 with FIPG to make me comfortable with it alone.

The small OEM bead failed at around 95k miles on my ‘12…along with 3 coolant services during that time

 

[electro992]

I normally do as well…but overall feel OEM setup ..and IMO… is a weak design flaw…a few too many redo’s reported on the 460 with FIPG to make me comfortable with it alone.

The small OEM bead failed at around 95k miles on my ‘12…along with 3 coolant services during that time

@Acrad Correct me if I am wrong, but I believe what looks like a bead there is actually the squeeze out of sealant on the inside.

The J2Hundy gasket does look less prone to installation error. Looks like it is made of Durlon 8500.

@Taco2Cruiser @MTKID @lx200inAR @wknd wrlrd any updates on how your gasket installs are holding up?

 

[Acrad]

It did appear to squeeze out on the inside.

Vendor did recommend razor thin/smear of Permatex High Temp Gray RTV on gasket so I applied that.

I haven’t come across any reports of failures since this gasket was released in early 2025…other than the installation issue by a member here who apparently used wrong torque numbers.

 

[electro992]

I did some further research on the J2Hundy gasket. The manufacturer of the gasket material, Durlon, provides a chemical resistance chart for their products including the 8500 material used by J2Hundy. Toyota Super Long Life Coolant listed ingredients are ethylene glycol, diethylene gycol, sebacic acid, and potassium hydroxide. Durlon shows a "caution" rating for potassium hydroxide with Durlon 8500. I don’t know the particulars of why that rating was given, but that is enough to steer me away from the J2Hundy product.

 

[Acrad]

If there is a long term issue hopefully the trace level exposure amounts to potassium hydroxide still gives me over 100k miles before issue crops up again.

Are these charts based on immersion into 100% solution levels of said chemicals/compounds?

I see there is another company seelling one here for the 3UR

SPMS 3UR Valley Cover Gasket

The SPMS 3UR Valley Cover Gasket is a high-quality automotive gasket designed for sealing and taking place of the Toyota sealant, used from OE. Made from AFM materials, this gasket is specifically designed to fit the valley cover of the Toyota / Lexus 3UR engine. This is to ensure a secure seal...

suckerpunchmotorsports.com

 

[MTKID]

@Acrad Correct me if I am wrong, but I believe what looks like a bead there is actually the squeeze out of sealant on the inside.

The J2Hundy gasket does look less prone to installation error. Looks like it is made of Durlon 8500.

@Taco2Cruiser @MTKID @lx200inAR @wknd wrlrd any updates on how your gasket installs are holding up?

I don’t enough miles on mine to give any feedback yet

 

[bloc]

I have a bit of experience with fiber based gaskets in different applications. Very good gasket material for flanges that are designed for them. Ours are not.

 

[Acrad]

Looking around I’m seeing more interest in using these gaskets on other Lexus vehicles that utilize UR engines so we’ll have a larger sample pool of how well this will work long term. If I come across any failures I’ll report back. I imagine we are only talking a few hundred or so in use at this point since released in early 2025.

 

[electro992]

Knocked out the job this weekend and it was not bad at all. The only issue I encountered was both of the vacuum hoses that attach to the valve covers (arrows below) were brittle and cracked upon re-installation. Part numbers for these are 12263-38010 and 12262-38020.