Our oil change place (a reputable transmission shop) told us that during our oil change the aluminum oil pan had stripped due to electrolysis with the steel drain plug, and that our oil pan would need to be replaced for $1,100. However, everything I have checked online and with another mechanic indicates this is nonsense, that the only way this can occur is because of overtightening. Is it possible for electrolysis to destroy an oil pan in this situation?
Possible…but very unlikely. I’ve never seen it. Have them show you and take pictures.
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The material selection is backwards… the pan should be steel and the plug aluminum. At least the aluminum plug will strip first… and easy replacement. I’d use an aluminum plug in an aluminum pan, too.
Agree with Mike, unlikely… the pan was stripped by a moose that overtightened the plug.
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Yes.
Also known as galvanic corrosion, electrolysis happens when two dissimilar metals are directly connected causing the lesser of the two metals to corrode. For the process to occur, the two metals have to also come into contact with a conductive electrolyte.
Tester
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Would this occur in an oil pan given that there is a thin film of oil between the two metals?
Certain steels can react with aluminum under the right conditions but they are fairly close in the galvanic series so not hugely reactive. In addition, if this is the OEM plug, it likely has a passivated coating to prevent galvanic corrosion. No manufacturer would use a plug that would be expected to corrode in contact with the pan material. So as long as it’s the OEM plug it’s far more likely the thread damage is from overtightening and stretching the threads to failure or a ham fisted oil jockey cross threading the plug in a prior service.
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Very unlikely. There are hundreds (thousands?) of posts from Honda owners here, yours is the first I remember on this topic. If Honda oil plugs were corroding their oil pans, it would be a popular complaint!
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I have a 2000 Chevy S-10 with a 4.3L V6. This engine has a cast aluminum oil pan that is basically a structurally important part where the transmission mounts up and all. This truck is coming up on 23 years old in a few months and I have ALWAYS changed the oil myself with a few exceptions where I was traveling and didn’t have oil change stuff with me.
The oil pan is cast aluminum and the plug is steel. There has NEVER been an issue for me with this and I suspect the same is true for others. Most lawn mowers are the same way if they even HAVE a drain plug anymore. So many are made to be changed by tipping them over and dumping the oil out the fill or not changed at all which I think is a HORRIBLE idea. Again, I have never had a problem removing a small engine drain plug from the cast aluminum block or pan on any of these so I think their explanation is crap.
If I were you, I would take this thing to another shop and have a new hole tapped for an oversized plug and not replace the pan. I am not sure if this is possible on your Honda but would certainly be doable on my S-10 so am assuming there would be no reason you couldn’t do this.
Galvanic corrosion is definitely a thing in certain situations but I don’t think this is one you need to worry about.
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Yes.
When the old oil is drained, it contains acids.
When drain plug is reinstalled, there’s a thin coating of this old oil between the plug and the oil pan.
This acts as an electrolyte and the electrolysis occurs.
I’ve run into this problem a few times over the years.
Tester
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They stripped the drain plug, probably with an air impact tool, and now want to over change you for a new oil pan.
I would drill and tap to a larger size before spending that kind of money on a new oil pan. Flush with keroscene to get the burrs out.
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Here’s a tip- If you liberally apply petroleum jelly, axle grease or some such concoction to the drill and tap, the chips will come back out with the tool. Just drill slowly so it’s not flung off or overheated and melts away.
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No experience w/that problem on oil pans, but I think it is best practice in general to not use mixed metals that are in direct contact w/each other. I’ve had electrolysis problems in house plumbing, copper fitting in direct contact w/steel pipe, over course of 10-15 years started to leak a little. Plumber told me common practice is to insert a brass fitting between pipes of the two different metals.
If it would cost $1,100 to replace an oil pan, cheapo me, I’d be trying to come up with a less expensive solution. It’s just an oil pan after all, no moving parts. Worse case, remove the pan, clean, then put it on the work bench, and stare at it for a while, some idea will likely come to mind.
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Find a shop who can repair the pan with a Time-Sert.
Tester
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Once this problem is solved OP, be sure to insist shop installs a new washer under the drain plug each time it is removed. If they don’t keep new Honda washers in stock, buy a bunch of them next time at the Honda dealership, then give one to the tech each time. New washer helps prevent leaks, so less likely they’ll overtighten.
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Aluminum can cold weld to other aluminum. So an aluminum bolt can’t be used in an aluminum pan!
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That’s a stretch, you don’t need an air tool, probably just your above average idiot with a wrench, aluminum is easy to strip out.
If you are changing the oil once a year, that will never be a problem. But then again neither will electrolysis.
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Is this car still in the shop?
The first thing I would do is use a roll forming die, also called a thread restoring die on the existing hole. If there is still some thread left, a roll forming die will restore the threads.
Roll forming dies use pressure to restore the threads instead of cutting new threads. With roll forming dies, no metal is removed and the restored threads are actually stronger than the original cut threads.
However with aluminum pans, the original threads were probably roll formed instead of cut because it makes a much stronger thread.
But, electrolysis is not the cause of your damaged threads. I would first blame cross threading but most drain plugs have a nose on them that prevents this. But we hear about stripped oil pan drains here all the time on both aluminum and steel pans and we all know it is due to an inexperienced and/or untrained “oil change technician”. Impact wrenches are often involved.
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The car is not in the shop at this time. The mechanic was able to install what he called a temporary plug, but recommended we get the oil pan replaced soon.
Don’t replace the pan, find a shop that can repair it.
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If you look at the drain plug and it looks like a normal bolt, then it is not a temporary plug. The may have used something like a thread locker on the regular drain plug. If that is the case, I’d find a place that will roll form the threads before I did anything else. Drill and tap to the next larger drain plug would be the next choice but I’d still want the new threads roll formed instead of cut. You may have trouble finding a shop that has roll forming dies or knows how to use them though.
If you truely trust the shop you have been using, you may be able to rent a roll forming die kit, aka thread restoring kit from a local auto parts store like O’Reilly’s (my local O’Reilly’s has one in their tool loan program) and take it to the mechanic and have them do this on your next oil change. Check in advance.
Edit: using a thread restoring die on the existing threads isn’t difficult, but using one to from new threads is a little different. The main difference is the size of the hole drilled is a little larger than the hole for cutting die as the roll forming die does not remove any metal.
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