Best way to clean and remove rust under body before undercoating.

[theperfectv]

So i bought a pretty nice 2018 sierra slt premium plus with low miles at a good price last week in michigan. Well after getting it in the air i noticed that it has a lot of rust for an 18. Almost looks like the sand on the roads had sand blasted it. I want to clean everything and get the undercoating done. And possibly spray all the other parts that are not coated by the undercoating. Are there any good sprays to soak this down before pressure washing? Does anyone else have this amount of rust also?

[theperfectv]

[dieselfan1]

Too late for undercoating. IMO.

You'll just be encasing the rust and it will rot from the inside out.

How many miles are on it?

They never washed it much I bet.

If it was mine....Powerwash it to get the dirt off and spray everything with Rust Reformer

 

[newdude]

20 hours ago, theperfectv said:

So i bought a pretty nice 2018 sierra slt premium plus with low miles at a good price last week in michigan. Well after getting it in the air i noticed that it has a lot of rust for an 18. Almost looks like the sand on the roads had sand blasted it. I want to clean everything and get the undercoating done. And possibly spray all the other parts that are not coated by the undercoating. Are there any good sprays to soak this down before pressure washing? Does anyone else have this amount of rust also?

 

 

I've seen that before.  Lots.  

 

Ex Canadian truck?  These northern state dealers so NY, MI, PA, VT, CT, MASS buy trucks out of Quebec or Ontario (because exchange rates were in favor quite a bit on our end).  Lots of them come from fleet or rental companies.  I can see sand and lots of it.  Seen 2019s and 2020s that look like this too.  The way your exhaust looks is a dead giveaway for me if I'm right about it being Canadian.  The scaley and the sandy/brown colors on everything.  

 

Scan the QR barcode in the driver door jamb, that's the RPO label (SPID label) and look for Z49.  

 

GM has a procedure for re-doing the peeling wax on these trucks.  Strip the wax with a wax remover/grease remover, wire brush or big whizz wheel the frame clean, use Lloyd's pure prep, followed by Lloyd's Kryptonite and then Daubert NoxRust 121B.  The Lloyds Kryptonite bonds to the bare metal unlike a paint that can easily scrape off.  

 

Bulletin below:

 

19-NA-255 1..10 (nhtsa.gov)

Edited December 1, 2021 by newdude

[rlcole321]

I live at the beach, so I just use Ospho (phosphoric acid) to spray the under carriage. just don't get it on the paint. It comes in different strengths so get a fairly med. strength, Paint and body suppliers carry it. It converts the iron oxide to iron phosphate. It's even paintable. But you do have a lot of rust, so it may take a lot.