Rednroll

A few weeks back I got a P0128 CEL code. I suspected my thermostat needed to be replaced.

I purchased the replacement thermostat online and I was assuming it would come with a thermostat housing gasket but it didn't. So I went to the local Autozone and picked up a gasket for $7.00. I told them I needed a thermostat housing gasket for a 2009 Wrangler 3.8L and they got the part for me.

However, when I went to replace my thermostat I noticed there was no original gasket. There was absolutely no gasket material between the 2 mating surfaces.
Here's what my old thermostat looked like once I removed the thermostat housing. No gasket material on the housing side as well.


I watched this install video prior, where they also noticed no gasket material and assumed that was the reason theirs was leaking.
(Jump to 10:35 where they remove the thermostat housing)

It seems to me that the 3.8L doesn't come with a thermostat housing gasket from the factory. At least it doesn't on my 2009 and whatever year JK they had in the video. What surprised me is that when I asked for a replacement thermostat housing gasket from Autozone there is obviously a replacement part available for one that doesn't seem to exist from the factory.

It looks like the way the housing seals to prevent coolant leaking is that there is a rubber ring on the thermostat that fits between the 2 mating surfaces. I decided to go ahead and install the gasket since I already purchased it but it really made me wonder if the gasket is needed or not and what's the reason there is a replacement gasket available if there seems to not have been one there from the factory?

Here's my old thermostat....yep, it looks like it needed to be replaced. One of the side brackets which holds the spring tension broke. It lasted 165K miles, so no complaints.

karls10jk

I noticed the gasket issue too. I bought it even though I read there wasn't one in there and I ended up returning the gasket. The factory stuff worked well enough for me, I didn't see a reason to add more material in there.

BoredKender

I just used the instant gasket goop when I changed mine out.

Rednroll

Thanks! I had some troubles installing the rear housing bolt. You know Murphy's law where it's always the harder to access bolt which gives you grief. It felt like it may have been cross threaded from the factory. Even trying to screw that rear bolt in without the housing, making sure it was perfectly staight going in and just threading it into the manifold threads it felt tight screwing it down. Much tighter than the front bolt which I could screw in just using my fingers.

In my case I think the extra material of the gasket may have helped me since it meant a couple threads less I needed to tighten that bolt down.

I was praying the whole time this simple repair wasn't going to turn into me having to pull the manifold to re-tap the treads, crack the plastic thermostat housing or snap that bolt.

It all seems good so far but will need to monitor for leaks over the next week because I was unsure if the rear bolt was down tight enough and was afraid to go too tight where using a torque wrench would have been futile due to the partial cross threading from the factory. I just went by feel/sight using a 10mm ratchet wrench.

ronjenx

The parts book and the service manual show no thermostat housing gasket.

If the thermostat has a rubber ring on it, installing an additional gasket will prevent that ring from sealing. It probably won't be a problem, but the parts won't be installed a designed.

Rednroll

Thank you Ronjenx, that was one of my concerns. The gasket is designed with an inner rubber ring which seems its intent is so it doesn't interfere with the ring on the thermostat. When I was at Autozone it did list a part in their system as "Original equipment part" which they didn't have in stock but I'm not finding a Mopar Part Number for the gasket, so possibly a Mopar part does not exist. So maybe the gasket is an aftermarket part only and is not required for the install and may cause interference with the thermostat rubber seal as you mention.

Here's a Mopar diagram of the thermostat/housing component assembly and I'm not seeing a gasket there as well.

Bigguy45

there is no gasket for the housing. the rubber o ring around the tstat is the seal. chrysler does this on a lot of their vehicles nowadays.

HostileJK

Felpro was making an updated gasket for the 3.8, try searching online it should have blue tracings on it. stopped my leaky bastard.


https://www.rockauto.com/en/moreinfo...1433839&jsn=13