For crossing rivers & mudholes I wan’t to preserve my 4wd as best I can. It seems there are two types of rust coatings that are usually recommended.
The permanent hard coat type & the product that you re-apply annually. For now I wan’t to go with the later & try something like corrosion X. I just don’t really know where exactly you are suppose to spray & what areas to avoid? I’ll I know is the brakes, rims, exhaust should be avoided.
My 4wd I recently brought is about 16years old & mostly seen city roads, but there is rust in various places already like door holes where the water drains, a few places under bonnet near frame & I can’t tell under body really maybe a lite layer on some axle areas. The towball receiver inside was a bit rusted too.
Hmm… I’ve been driving 4x4’s for 40 years. I really don’t see a point to trying to rust proof them any more than any car. And I don’t see a point to rust proof a ‘city’ car either. Really, they are getting just as much water and gunk on them as a 4x4 might.
There really isn’t a need to rust proof frame members (I assume you are talking about body on frame and not a unibody). Not much you can do about body panels.
IMHO of course, it will be interesting to see other responses.
If you do this, also make sure not to get anything on the driveshaft (propeller shaft). It rotates rapidly and even small imbalances can cause unwanted vibration.
I don’t know anything about different undercoatings so I’m off topic here, but I don’t think you need to rustproof it for rivers and mud. However, rustproofing because it’s 16 years old might make sense. Your rust sounds normal though. You may be able to clean it off the body with some WD-40 and a rag. The axle and hitch are nothing to worry about. Rust doesn’t hurt big thick pieces of metal like that.
When it comes to mud, it’s really worth it to wash underneath the vehicle afterward. It’s no fun working on a vehicle when everything is covered in dried up mud. You can spray cooking spray underneath before you go offroad to make cleanup easier.
Eh. To continue my first response, I think that the OP should just relax. My '76 Chevy truck went through hell that only a young 4x4 enthusiast could give it. It’s still on the road with no problems with the under carriage.
There is really no way IMHO to cover every thing on a used car with some sort of spray. And really no point to it. Axles and frames do not rust through. They will get a little on the surface and stop rusting (a little rust prevents oxygen from getting to it).
If the OP returns, What type of vehicle, and what type of off road do you do?
You can’t rust-proof over existing panel rust. That has to be cut out and replaced. Or simply ignored. Agree with the folks above that surface rust on frame members and such is utterly immaterial and must be ignored.
Said another way, the vehicle already has the rust you’re stuck with. The sensible goal going forward is to minimize additional rusting of the only stuff that matters: body panels.
The tool you use to do that is called “wash all the dirt & road salt off regularly”. With an ordinary hose, soap, mop or rag, & bucket.
Fancy spray-on coatings might be useful on a brand new vehicle. Mostly they’re a way to sell hope to rubes.
I ruined a 1970 Dodge Ram 4X4 set o axles because I had the axles under water for long periods and did not know to drain & replace the differential oil after deep water.
How do the new 4 wheeler cover this? I thought there really was a need for a vent due to the normal change in temps inside the differential even in normal driving conditions.
I understand the whole cleaning & drying is more important. But what about in cold periods where it’s wet for days on end? Shouldn’t the majority of the underbody be coated with something if it’s going to stay wet for say 3-5days constantly?
I see videos online people preparing their 4wd for the winter. I see that these rust prevention are a waste, but only if your vehicle has a chance to dry up.