Preventative Maintenance Plan Guidance (WWYD?)

[adventurenali92]

If you haven’t already, I would do all seals related to engine oil. My 2006 LQ4 leaked oil from every seal it could through the second half of 100k range. Valve cover gaskets I did myself, known leak point and they’re super simple to do in the driveway. First time I did them it took me a whole day cuz I hadn’t done it and was taking my time and making sure I did everything right. Just swapped them again when I replaced my pickup tube o ring in late March of 2025, and valve covers were both done in like two hours. Had my previous shop do valley pan gasket, rear main seal, and oil pan gasket. Also, the o ring on pickup tube in the bottom of the engine is a known failure point causing low oil pressure. I had it replaced preventively in June of 2022 at a different shop after my previous one went out of business. bought a genuine GM pickup tube and o ring from a Chevy dealer as I wanted the correct GM parts, only for the shop to not use it. Or the correct o ring. Shop used a cheap o ring and it failed in less than 50,000 miles and barely three years. It still ran totally fine enough for me to baby it back home and get it parked in the garage, and luckily I didn’t damage my engine but I was pretty pissed to find the wrong cheap o ring on the pickup tube when I tore it all apart myself. So if you decide to do it yourself or have the job done, make sure you get the red o ring for the tube. That’s the correct one per GM. Not as difficult of a job as I originally thought it would be. I also slapped a new oil pan gasket on when I buttoned it all back up with the new o ring on the pickup tube and getting the rtv sealant on the correct places on the corners of the pan was pretty simple. Hasn’t leaked a drop oil since then thankfully.

 

[SilverSport]

GT4 is the RPO for a 3.73 gear ratio...I have it as well...I thought the LSD was G80...my Yukon Denali does not have that...perhaps they discontinued the LSD by 2005...

thanks,

Bill

 

[S33k3r]

Nope. My wife's 2005 Suburban 2500 has an LSD. I'll have to check my daughter's RPO codes on her 2005 Suburban 1500, though.

 

[SilverSport]

...I meant perhaps they discontinued the LSD for the AWD GMC Yukon Denali by 2005 since OP’ers 2003 has one and my 2005 does not (and I don’t show it was optional for 2005)...

Bill

 

[OneofFew]

I would drain the trans pan every time you do an engine oil change. That will drain about 4 qts.
My pan has a drain plug

 

[nonickatall]

I would drain the trans pan every time you do an engine oil change. That will drain about 4 qts.
My pan has a drain plug

This offers no advantage; it's far too complicated and technically inefficient, since, as you already mentioned, you can only remove 4 quarts.

You don't need to change the filter with every oil change, as it only filters out metal particles. The filter isn't designed to retain combustion residues or abrasion particles like an oil filter in the engine. Therefore, it's not necessary to open the pan every time.

It's much easier to disconnect the upper fitting on the automatic transmission's oil cooler, located on the passenger side, and attach a hose. Start the engine very briefly until no more oil comes out.

You need to collect the oil to measure how much came out. Then refill with the same amount of oil and repeat this process until fresh oil comes out. This is equivalent to a transmission flush. This completely replaces the transmission fluid. It can be done in half an hour.

Doing this every 60,000 km is sufficient. Of course, more frequent flushing won't hurt.

I'm not saying it doesn't make sense to change the transmission filter occasionally, for example, if you don't know how long it's been since it was last done. But if you change the transmission fluid every 30,000 km, for instance, you don't need to change the transmission filter every time.

 

[nonickatall]

In my opinion, an important preventative maintenance step is replacing the oil pump's O-ring, as these tend to leak eventually, causing the oil pump to draw in air, which is extremely bad for the engine. While you're at it, you should also replace the bypass valve in the oil pan, as these can also fail.

It's not a lot of work, but it's extremely important for the car's longevity.

Another thing I would do is add a liter of diesel to the engine before an oil change and drive about 20 to 30 km. This loosens all the carbon deposits. In my case, this eliminated the rattling of my hydraulic lifters and reduced my oil consumption.

Another important thing with our cars is checking the ground points and cleaning them.

And I think the most important thing, which Americans strangely don't seem to do often, is underbody rust protection. The cars themselves aren't very prone to rust in terms of bodywork, but the underbody, with its brake lines, unfortunately is.

Furthermore, it's important to clean the sunroof drains to prevent water from accumulating and leaking into the interior, and to lubricate the sunroof tracks.

Equally important is removing the door panels, treating the inside of the doors with rust protection, and lubricating the window regulator mechanisms.

 

[pronstar]

I’ve heard more than a few reputable transmission techs and builders refer to the filter as a “gravel trap” that generally needs to be cleaned/replaced once or twice in the transmission’s lifetime.

 

[nonickatall]

I’ve heard more than a few reputable transmission techs and builders refer to the filter as a “gravel trap” that generally needs to be cleaned/replaced once or twice in the transmission’s lifetime.

Yes, of course, changing the automatic transmission filter can't hurt, but it necessary to understand which different things are produced in an automatic transmission, that need to be filtered out.

Firstly, there's the wear from the friction linings, which is very fine and isn't filtered out by the filter; instead, it remains suspended in the oil and circulates through the transmission. Then there's the wear from the metal pressure plates, which is magnetic and is captured by the magnet in the oil pan.

In addition, small metal parts or shavings, for example from gears or other components, may break off. These are captured by the filter to prevent them from being sucked into the transmission by the oil pump, where they could cause damage. The filter's primary function is to filter out these larger particles and chunks.

If you want to perform perfect maintenance, it's advisable to remove the oil pan, check for significant metallic wear, change the filter, and then flush the transmission, because removing the oil pan only allows some of the oil to be removed from the transmission. The majority of the oil is located in the oil passages, the valve body, the pistons, the oil pump, the torque converter, and the oil cooler.

Since this is obviously a major undertaking and also adds up in terms of cost at a workshop, most people don't do it and leave their transmission untouched.

The maintenance that I consider far more important—namely, changing the oil—costs 10 liters of oil and half an hour of labor for our trucks. You don't even need a lift.

Changing the filter, on the other hand, is much more involved because I need a lift or a pit. I have to unscrew the oil pan, collect the oil, change the filter, and screw the oil pan back on—ideally in such a way that it's still sealed afterward.

The benefit of changing the filter is significantly less than the benefit of changing the oil.

Therefore, it's much more important to flush the transmission, and this works really well on our trucks because the lines on the oil cooler have quick-release couplings. So, you disconnect the quick-release fitting, attach a hose to the transmission hose, and briefly run the engine. This won't harm an automatic transmission.

Then you refill the removed oil and run the engine again briefly until the transmission has completely flushed its oil. This completes the transmission flush and oil change. You'll need about 10 liters of oil and half an hour.

Doing this at least every 40,000 km will greatly benefit your transmission.

If you have the time, inclination, and money, you can, of course, also change the filter every other time.

In my opinion, it's not necessary.