Oil undercoating before winter

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I always undercoat with bar and chain oil cut with a little bit of kerosene. The debate a buddy and me are having is I say to pressure wash the underside before, he says years of oil and dirt buildup protects more. Opinions?
 
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I think you are both right. Yes, the dirt that sticks to the fresh oil is going to help protect. My focus was like that when I went to install the trailer hitch this summer; I had to wipe it way. Underneath was a pristine unibody! However, it also collects salt. If you pressure wash off, you are going to be washing off the salt. I don't pressure wash, myself. Just spray on new oil every year.
 
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In years past I coated the seems of doors and finders with old engine oil and it worked very well.
 
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Originally Posted By: jdawg89
How does the Cherokee look?
Rockers are rusting (I have new ones). Frame is solid. I have holes drilled and also deposit oil in the "frame". With the issues I have been having with it lately, the solid "frame" is the only reason I still have it. Everything else is going to be crunchy. I bought the Cherokee used in 2010, so it already experienced a fewwinters. But wasn't very rusty at all.
 
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Originally Posted By: jdawg89
I always undercoat with bar and chain oil cut with a little bit of kerosene. The debate a buddy and me are having is I say to pressure wash the underside before, he says years of oil and dirt buildup protects more. Opinions?
I would not pressure wash it, why? Because the accumulation of the oil and dirt will highly resist wash off. Once few layers are built up, the coating will stay put for a long time and will not have to be re-coated every year.
 
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I always try to keep it Simple. I would not bother washing under my vehicle. But, one year before oil spraying (Fluid Film), I noticed a lot of dirt (1/16" - 3/16" thick) on the inside of fenders. Kind of had a 'sand dunes' pattern. I had to take a putty knife and scrape off the dried oil/dirt. The simple way was to just scrap and not wash. My vehicle is 12 years old with no rust. But it sure is messy to work under it.
 
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Originally Posted By: larryinnewyork
I always try to keep it Simple. I would not bother washing under my vehicle. But, one year before oil spraying (Fluid Film), I noticed a lot of dirt (1/16" - 3/16" thick) on the inside of fenders. Kind of had a 'sand dunes' pattern. I had to take a putty knife and scrape off the dried oil/dirt. The simple way was to just scrap and not wash. My vehicle is 12 years old with no rust. But it sure is messy to work under it.
I'd rather get greasy and dirty any day of the week than fight with rusty bolts!
 
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Originally Posted By: Miller88
Originally Posted By: larryinnewyork
I always try to keep it Simple. I would not bother washing under my vehicle. But, one year before oil spraying (Fluid Film), I noticed a lot of dirt (1/16" - 3/16" thick) on the inside of fenders. Kind of had a 'sand dunes' pattern. I had to take a putty knife and scrape off the dried oil/dirt. The simple way was to just scrap and not wash. My vehicle is 12 years old with no rust. But it sure is messy to work under it.
I'd rather get greasy and dirty any day of the week than fight with rusty bolts!
Same here. Once you break off few bolts and nuts that turn a simple job into a several hour endeavour, I'll gladly take a dirty, greasy underside. But then I work on my own cars and don't charge over $100/hour for labour, so I want as little “breakage” as possible.
 
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I have to change the front U Joints in my father's truck at some point. To do so, I need to remove the unit bearings. The truck has never been sprayed and it's rusty under there! In fact, the nuts are rusting apart ... I sprayed it with atf and acetone, next time I'm there I'll hit it with some PB Blaster. I'm planning on doing it around thanksgiving time so it should have time to do it's thing ... I hope.
 

Kestas

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Once, on a new car, I removed every fastener under the car that I could get to and treated the threads with antiseize. The few evenings I spent doing this saved me many evenings of fighting rusted bolts later on.
 
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I always undercoat with bar and chain oil cut with a little bit of kerosene. The debate a buddy and me are having is I say to pressure wash the underside before, he says years of oil and dirt buildup protects more. Opinions? But back to the 'original' question. What I have noticed is a little dirt won't hurt, and I don't worry about it. But to pressure wash the whole underside every year, that's to much work. A thin layer of dirt will just soak up the oil.
 
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A trip through a field of tall grass does a good job of cleaning the underside of a car. Seems to me about anything other than undercoat which is sprayed on gets washed off in the first big gully washer when deep puddles are driven through at speed.
 
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jdawg89

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Originally Posted By: HerrStig
A trip through a field of tall grass does a good job of cleaning the underside of a car. Seems to me about anything other than undercoat which is sprayed on gets washed off in the first big gully washer when deep puddles are driven through at speed.
Give it time to soak into the metal a bit, and not sure if you know what bar and chain oil is, but it's some nasty stuff, made to not fling
 
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The only downside I see to a layer of dirt is that in certain spots, it can act like sandpaper. Older Subarus had a plastic deflector plate between the wheel well and gas filler pipe that loved to get gritty and wear thru the pipe. I can see similar stuff happening with certain design wheel well liners and the fender lip if they got gritty.
 
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