Changed Thermostat - Now I Guess I Get To Pull Plenum Off!

[Flagship-Q]

Well damn, I changed my thermostat yesterday (stuck open, low operating temperature), and I noticed coolant in the valley under the plemium so I soaked it all up after changing it. Now it's still puddling under there and I traced it to the bottom of the thermostat housing where it mounts to the lower intake (blue O.E. RTV). I assume that I'll have to pull the plenum to reseal that, but I was wondering what else could be resealed while I have it off. Although my valve covers aren't leaking, I figured it would be a good time to do those also (never been resealed before). The under plenum hoses look in good shape but I won't entirely know their condition till I get in there. Since it's off I want to do it right the first time. Any suggestions or tips would be appreciated. Thanks alot!

[Q451990]

Your profile doesn't show the mileage - but on a 14year old Q I would replace ALL of the hoses under there. They're going to be brittle. The leak could very likely be the hoses that go between the left and right banks. I would inspect the knock sensors for cracking under magnification, and strongly consider replacing them and their harness if you're anywhere near 100K. Ohm your injectors while they're easy to get to, and check the harness and connectors for any corrosion. I would unplug everything electrical and put di-electric grease in there. Be sure to buy a case or two of brake parts cleaner (or BG throttle body cleaner) for the plenum, throttle body, rocker covers if you reseal them, EGR Valve, BPT Valve, and port. Buy some new rubber o-rings for the plenum to runner junctions - and a foot or two of fuel hose. Might as well replace the PCV valve while you're under there too.

Rocker covers have some overlap with plenum removal, but not a lot. If you decide to reseal them allow for an extra day to scrape and seal them. An angle griner with a "scrubby pad" attachment makes it a lot easier. I also like to let the RTV set up for 12-15 hours before running the engine too. I prefer the Permatex Grey over the Nissan orangy/red stuff. T3 uses BG Black, but I don't know if it's readily available.

Good luck!

Heath

[PopPop]

Sometimes the long 4-6" long 12mm bolt that is vertically installed into Thermostat Housing will leak! I think you have to remove it for easy access. If you removed this bolt it could be the guilty party!

[Q45denver]

Loctite 5900 has a pretty good reputation and is the same as Mercedes OEM. I've also tried a Permatex RTV and Nissan red. The the Nissan sealant seems much softer and more compliant when cured. I might try Hylomar next time. One of the nice things about Hylomar is that it can be put into service instantly. This is nice since you could start the car up and inspect for leaks while you have all the tools out.

[Flagship-Q]

Your profile doesn't show the mileage - but on a 14year old Q I would replace ALL of the hoses under there. They're going to be brittle. The leak could very likely be the hoses that go between the left and right banks. I would inspect the knock sensors for cracking under magnification, and strongly consider replacing them and their harness if you're anywhere near 100K. Ohm your injectors while they're easy to get to, and check the harness and connectors for any corrosion. I would unplug everything electrical and put di-electric grease in there. Be sure to buy a case or two of brake parts cleaner (or BG throttle body cleaner) for the plenum, throttle body, rocker covers if you reseal them, EGR Valve, BPT Valve, and port. Buy some new rubber o-rings for the plenum to runner junctions - and a foot or two of fuel hose. Might as well replace the PCV valve while you're under there too.

Rocker covers have some overlap with plenum removal, but not a lot. If you decide to reseal them allow for an extra day to scrape and seal them. An angle griner with a "scrubby pad" attachment makes it a lot easier. I also like to let the RTV set up for 12-15 hours before running the engine too. I prefer the Permatex Grey over the Nissan orangy/red stuff. T3 uses BG Black, but I don't know if it's readily available.

Good luck!

Heath

Thanks for all the info. The car has 102k and the front rubber hose that came out of the front of the thermostat wasn't cracked or brittle but the cover that the hose attached to was corroded so I scraped and cleaned it up (I presume that all hose connections will be like this). I Ohm'd the injectors and have to replace the #1. I have dealer documentation when the previous owner (at 97K) had the MAF, spark plugs, #3 injector, and O-rings/Collars/Gaskets replaced on the intake along with cleaning. I'm gonna do the chain guides at the same time so it'll be a whole weekend of wrenching.

[elwesso]

jus to be sure, you lathered RTV on the back side of the Tstat as well as on the cover, yes?

If your going under the plenum, you will want to have the hoses on.. the PCV hoses tend to crack.. when i did the guides for ross, i went to take a hose off with a pair of plyers and it shattered like it was glass.

[Flagship-Q]

Wes, the O.E. T-stat only seemed to have RTV on the front side (facing you between the front of the T-stat and the cover outlet). I didn't scrap any old RTV from behind the T-stat in the channel it sits in because their wasn't any there before. So to sum, I just RTV'd the front cover outlet and installed it onto the T-stat and the housing as it looks to be correct. It's not leaking from there but at the base of the housing it sits in at the manifold. I can see it seep at the mouting point (also blue RTV there aswell). I guess the only definite answer will be when I pull the plenum.