1999 Suburban driver - undercoat or not?

[DeadheadNM]

My 99 Suburban is rustfree, has 135k mi, and I'm the second owner. Now that I'm living in Wisconsin and expect to drive the sub occasionally during winter I'm wondering if undercoating is a good idea. I've never had a vehicle undercoated so looking for thoughts, tips, advice on whether or not it's worthwhile and if so what to look for in terms of a quality outcome. Thanks, Pete

[abig84]

I would. I brought my 86 up from the south 9 years ago 4 Chicago winters messed that thing all up, wish I would have when I got it. I just drive it in the winter anymore. I'm guessing there are places you can take it and let them do it

[greentruck]

I used to live a bit over an hour west of there in Stillwater. I would strongly recommend undercoating it. It would make me cringe when the snow starts to melt and that brine and salt slush gets into every nook and granny of that rust free truck. Tons of rust buckets rolling around over there.

[grumpyolddog]

I would oil coat it not undercoat it gear oil mixed with trans oil works great

[special-K]

The question with undercoat is does it help or hurt and the answer is yes and no. Great idea in theory, but in reality there is a chance the crud can get behind it and in those cases it traps the crud. If it was 100% absolutely sealed at all edges, left no areas unprotected, and sealed all crevices, nooks, and crannies that retain the crud then it would pretty much guarantee rust protection. I go with the flush it out at the car wash as often as possible method.I have slipped around on cake ice to do it. If the car wash is open I'm washing. Ice forms on the body as I spray, but I flush that underside as best I can. I know some freezes before it all flows out, but it doesn't allow it to pack itself in and it comes out the next time till the spring washes flush it clear. I know Maryland is milder than WI, so not sure of the car wash situation in winter.

[DeadheadNM]

Thanks for the feedback.

There are a fair number of automated drive through car washes here that I could use religiously during the winter. Maybe i should just spray heated cosmoline to the under surface this fall

[Willowrun]

Originally Posted by grumpyolddog

I would oil coat it not undercoat it gear oil mixed with trans oil works great

Do this.
I’ve been fighting rust my whole life. As a matter of fact, road salt outrages me. Anyways, I bought a few MI vehicles that have been under coated when I was young and dumb...never again. It’s just a superficial cover up of rust.
Beyond coating the undercarriage with oil or boiled linseed, also hit all seams with something like fluid film and as mentioned, religious car washes in the winter. You’ll get a few more years but the salt and brine always wins.
Anything I value as a vehicle is stored in the winter FWIW.

[DeadheadNM]

Thanks - I'll keep the winter driving to a minimum. I see square body GMs running around town regularly but as expected all have rust.

[Ironhorse]

Pete, can't help with the under coat question but just want to mention, I know exactly where you are located. Eau Claire is about 60 odd miles from Rice Lake where I was born, many, many years ago. Beautiful country in Wisconsin, rolling hills and pastures. Great fishing and hunting if inclined in that direction. Winters get cold and lots of snow as I remember. Good luck with your undercoat decision.

[Coley]

To my recollection most cars and trucks from the 70's and 80's were undercoated so in basic terms....it helps a bit but undercoating will not prevent rust out.
....it probably worked for as long as the warranty length was...lol

I am a firm believer in the Rust Check process (including the product 'Rust Check' or 'Krown' rust prevention), which I do myself for my '72 although I don't winter drive it.
It is much, much more in depth than simply spraying the bottom pan of the vehicle in 5-10 minutes...but it takes work to 'do' it to the truck.
(In Canada we obviously get a lot of snow and salt on the roads so it makes some sense to have come across some processes and products that work to keep the vehicles solid....google 'rust check' and see if it is something you might be interested in trying)
You have to be prepared to access INSIDE the doors and INSIDE the rocker panels, remove tail light assemblies, work from both inside, outside and underneath the truck.
It probably takes me 2 dirty hours to do my truck and most of that is spent on my back underneath it.
By the time I'm done I'm pretty dirty and ready for a good shower.
Most guys I know are only into washing the vehicle, which is ok but that isn't going to stop anything from rusting out unfortunately.
That said, when the 'rust checking' is done.....serious piece of mind in terms of keeping the rust away.

All good
Coley

[Travisarmenta]

Originally Posted by special-K

The question with undercoat is does it help or hurt and the answer is yes and no. Great idea in theory, but in reality there is a chance the crud can get behind it and in those cases it traps the crud. If it was 100% absolutely sealed at all edges, left no areas unprotected, and sealed all crevices, nooks, and crannies that retain the crud then it would pretty much guarantee rust protection. I go with the flush it out at the car wash as often as possible method.I have slipped around on cake ice to do it. If the car wash is open I'm washing. Ice forms on the body as I spray, but I flush that underside as best I can. I know some freezes before it all flows out, but it doesn't allow it to pack itself in and it comes out the next time till the spring washes flush it clear. I know Maryland is milder than WI, so not sure of the car wash situation in winter.

Could not agree any more. The undercoating issue, at least in the past has been Trapping the moisture and salt, once you let it sits all it does is eat away.

Once I find the time, I'm gonna crawl under both my Sub and my Jeep and Por15 every piece of metal I can.

[DeadheadNM]

Originally Posted by Ironhorse

Pete, can't help with the under coat question but just want to mention, I know exactly where you are located. Eau Claire is about 60 odd miles from Rice Lake where I was born, many, many years ago. Beautiful country in Wisconsin, rolling hills and pastures. Great fishing and hunting if inclined in that direction. Winters get cold and lots of snow as I remember. Good luck with your undercoat decision.

Come back! The countryside where we are just south of town is beautiful. I've got my fishing license and hope to have time to try turkey hunting in the fall. Lots to do here. We'll see how winter goes

I'll be in Rice Lake later this month - will think of you. I've heard from several locals that it's scenic a great place for hunting and fishing.

[DeadheadNM]

I found a local shop that does rust checking in the manner that Coley describes and uses a cosmoline compound - I'm going to drop by and chat with them. Pricey though: http://www.rustcoaters.com/home-1.html

[notsolo]

Looks like a good, quality system. Money well spent IMO...You know your truck is in good mechanical condition, unless your going to drive a beater for 6 months a year.

[Coley]

Here is an example of the 'peace of mind' within using this 'rust check' process and product.
When you are under the truck cab looking back and up at your rocker panels...you will see (2) small 1/2" long slots or perforations in the bottom on the rocker panel...where the vertical meets the sloped.
These slots allow access up and into the insides of the rocker and normally act as a drain hole for moisture, etc....although over the years they plug up with dirt, pine needles, etc.
This is where I take the rust check and its WD40 similar 'squirter straw' and shoot up inside the rocker panels...both directions, up, down, back and forth, hitting every surface INSIDE that rocker panel.
Remember...washing the outside curved section is easy...but it always rusts from the inside out, not the other way around.
Ok, that way you have applied this rust check product INSIDE the rocker where the rust is more likely to be starting or growing and you can shut it down or control it.
....this is just part of the whole process, but if you get a chance get under your truck (67-72') and check these slots out. These are job 1 in my books.
....just note tho'...you will get hit with some drip when you do these....so clean up, smile and sleep tight knowing that stuff is in there keeping the rust away.

All good
Coley