| Author |
Message |
oprn
Samba Member
Joined: November 13, 2016
Posts: 15015
Location: Western Canada
|
 Posted: Mon Oct 13, 2025 3:05 am Post subject: Case sump rot |
 |
|
I see this problem rear it's ugly head over and over on this site. It's always about "how do I fix this", how about a discussion on prevention? If we treat an engine right this should never happen.
I stole this photo from Moyock13's post. My apologies to you Sir!
In my view it is caused by running an engine too cold and not changing oil often enough. So easy to prevent this!
_________________
Our cars get old, we get old but driving an old VW never gets old! |
|
| Back to top |
|
 |
Glenn 
Mr. 010
Joined: December 25, 2001
Posts: 79984
Location: Sneaking up behind you
|
| Posted: Mon Oct 13, 2025 4:33 am Post subject: Re: Case sump rot |
|
|
Caused by water, either sitting on a wet floor or water inside by not letting the engine get hot enough to boil it off. Fewer very short drives and installing shroud flaps and thermostat will help.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare
עַם יִשְׂרָאֵל חַי |
|
| Back to top |
|
|
petrol punk
Samba Member
Joined: August 21, 2007
Posts: 1046
Location: Las Vegas, NV
|
| Posted: Mon Oct 13, 2025 9:50 am Post subject: Re: Case sump rot |
|
|
I thought this only occurred on engines that were sitting in the dirt. I didn't think it ever happened on engines in use.
_________________
36hp '56 European DeLuxe oval
'70 bug 1835cc |
|
| Back to top |
|
|
Bobs67vwagen
Samba Member
Joined: March 27, 2005
Posts: 678
Location: Eastern north carolina
|
| Posted: Mon Oct 13, 2025 10:45 am Post subject: Re: Case sump rot |
|
|
| I have a ak engine that came out of my friends 74 bug when it was totaled by a garbage truck while parked on long Island in the 1980s. I used this motor in several bugs and buses over the years and always kept fresh oil in it, and when not in use kept it in a garage on a piece of wood over cement blocks. This motor now has this deterioration on the bottom. It is really a shame as this motor has never been opened and was never driven hard and taken care of. So you can take care of them but may not be able to prevent this from happening. I agree with Glenn's theory that water will settle in the bottom of the case and eventually cause this issue. |
|
| Back to top |
|
|
U&I
Samba Member
Joined: July 09, 2024
Posts: 86
Location: Oregon
|
| Posted: Mon Oct 13, 2025 11:47 am Post subject: Re: Case sump rot |
|
|
Yes, water being denser than oil and the fact that the two do not mix allows the water to gravitate below the oil causing the bottom of the case to rot if left unchecked.
Then there is the issue of electrolysis, whereas dissimilar metals in contact with water can create rot in the weaker material, this is the theory behind the anode rod that you find in water heaters, essentially the anode is sacrificial so as not to rot the steel tank.
Anode rods can be purchased in aluminum and magnesium
This case sat on the floor boards of a Baja that took on water due to leaks, the rot is evident.
|
|
| Back to top |
|
|
Clatter
Samba Member
Joined: September 24, 2003
Posts: 7805
Location: Santa Cruz
|
| Posted: Mon Oct 13, 2025 7:15 pm Post subject: Re: Case sump rot |
|
|
| Bobs67vwagen wrote: |
| I have a ak engine that came out of my friends 74 bug when it was totaled by a garbage truck while parked on long Island in the 1980s. I used this motor in several bugs and buses over the years and always kept fresh oil in it, and when not in use kept it in a garage on a piece of wood over cement blocks. This motor now has this deterioration on the bottom. It is really a shame as this motor has never been opened and was never driven hard and taken care of. So you can take care of them but may not be able to prevent this from happening. I agree with Glenn's theory that water will settle in the bottom of the case and eventually cause this issue. |
Did this engine always have a functional thermostat and flaps when it was being used?
_________________
Bus Motor Build
I have excellent news for the world...
There is no such thing as patina.
It does not exist! |
|
| Back to top |
|
|
oprn
Samba Member
Joined: November 13, 2016
Posts: 15015
Location: Western Canada
|
| Posted: Tue Oct 14, 2025 5:00 am Post subject: Re: Case sump rot |
|
|
| petrol punk wrote: |
| I thought this only occurred on engines that were sitting in the dirt. I didn't think it ever happened on engines in use. |
No these engines are rotting from the inside. It's strictly a care and feeding problem. It happens during use. It's water in the oil combining with Sulphur in the fuel to produce Sulphuric acid, water combining with nitrogen to produce nitric acid. Once Sulphuric acid is present it is too late to boil it off. Boiling point is 638.6*F. The only recourse at that point is to dump the oil and replace it. Nitric acid boils at 181.9*F and will boil off with the water.
I have seen engines that have sat out in the weather and that is not what does this either. They have rotted out heads and seized pistons and cylinders from open valves and water going down the intake and into the exhaust ports.
_________________
Our cars get old, we get old but driving an old VW never gets old! |
|
| Back to top |
|
|
oprn
Samba Member
Joined: November 13, 2016
Posts: 15015
Location: Western Canada
|
| Posted: Tue Oct 14, 2025 5:29 am Post subject: Re: Case sump rot |
|
|
| Clatter wrote: |
| Bobs67vwagen wrote: |
| I have a ak engine that came out of my friends 74 bug when it was totaled by a garbage truck while parked on long Island in the 1980s. I used this motor in several bugs and buses over the years and always kept fresh oil in it, and when not in use kept it in a garage on a piece of wood over cement blocks. This motor now has this deterioration on the bottom. It is really a shame as this motor has never been opened and was never driven hard and taken care of. So you can take care of them but may not be able to prevent this from happening. I agree with Glenn's theory that water will settle in the bottom of the case and eventually cause this issue. |
Did this engine always have a functional thermostat and flaps when it was being used? |
^^^This is part of the problem.^^^
The other part is people who think they are being kind to these old cars by not driving them hard, by never taking them out of town on a good long highway run. You are not doing it a favor by babying your engine. Quite the opposite!
_________________
Our cars get old, we get old but driving an old VW never gets old! |
|
| Back to top |
|
|
Glenn
Mr. 010
Joined: December 25, 2001
Posts: 79984
Location: Sneaking up behind you
|
| Posted: Tue Oct 14, 2025 5:32 am Post subject: Re: Case sump rot |
|
|
| oprn wrote: |
Did this engine always have a functional thermostat and flaps when it was being used? |
^^^This is part of the problem.^^^
The other part is people who think they are being kind to these old cars by not driving them hard, by never taking them out of town on a good long highway run. You are not doing it a favor by babying your engine. Quite the opposite![/quote]
^^^^^
THIS
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare
עַם יִשְׂרָאֵל חַי |
|
| Back to top |
|
|
raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23305
Location: Oklahoma City
|
| Posted: Tue Oct 14, 2025 5:50 am Post subject: Re: Case sump rot |
|
|
| oprn wrote: |
| petrol punk wrote: |
| I thought this only occurred on engines that were sitting in the dirt. I didn't think it ever happened on engines in use. |
No these engines are rotting from the inside. It's strictly a care and feeding problem. It happens during use. It's water in the oil combining with Sulphur in the fuel to produce Sulphuric acid, water combining with nitrogen to produce nitric acid. Once Sulphuric acid is present it is too late to boil it off. Boiling point is 638.6*F. The only recourse at that point is to dump the oil and replace it. Nitric acid boils at 181.9*F and will boil off with the water.
I have seen engines that have sat out in the weather and that is not what does this either. They have rotted out heads and seized pistons and cylinders from open valves and water going down the intake and into the exhaust ports. |
You beat me to it.
Yes, water alone will eventually cause SOME heavy corrosion....but that is not what what this is.
And, as U&I mentioned, you have what is essentially an "accelerant" which is the galvanic action between the steel studs and magnesium.
Galvanic action requires an electrolyte. The water with the dilute sulfuric acid created by the sulfur in the oil breaking down added with any metallic salts present in the oil...IS....the electrolyte.
The most common metallic salts in motor oil are magnesium and calcium.
If the oil left sitting in the engine case for a long time on the shelf or in the car is also dirty....it has lots of carbon and sulfur and some moisture. Over time with ambient temp rising and falling ...will put a lot more condensation into the oil.
Thinking about this, one had to store magnesium cases for extended periods, say....out in the shed or an unheated garage....I would take the oil out, clean them well and either paint them with something (even cheap paint will really slow this down), or paint them with ATF and bag them up nearly airtight....or even that WD-40 long term protectant spray which is like cosmoline.....should work.
Ray |
|
| Back to top |
|
|
oprn
Samba Member
Joined: November 13, 2016
Posts: 15015
Location: Western Canada
|
| Posted: Tue Oct 14, 2025 6:03 am Post subject: Re: Case sump rot |
|
|
| U&I wrote: |
Then there is the issue of electrolysis, whereas dissimilar metals in contact with water can create rot in the weaker material, this is the theory behind the anode rod that you find in water heaters, essentially the anode is sacrificial so as not to rot the steel tank.
Anode rods can be purchased in aluminum and magnesium |
^^^This ^^^ and what Ray said about electrolysis is totally valid.
I am somewhat familiar with the use of sacrificial anodes in crude oil and water storage tanks. Would it, could it be used in our engines? I don't know. Just changing out that 2.5 quarts of oil seems the simpler solution.
...and of course insuring that the engine is running hot enough is the first line of defense!
_________________
Our cars get old, we get old but driving an old VW never gets old! |
|
| Back to top |
|
|
Bobs67vwagen
Samba Member
Joined: March 27, 2005
Posts: 678
Location: Eastern north carolina
|
| Posted: Tue Oct 14, 2025 6:23 am Post subject: Re: Case sump rot |
|
|
| The ak engine I referred to was totally stock with thermostat. In between uses in different vehicles it was stored with fresh oil. My original thought was that the high humidity on long Island contributed to the problem. This engine was routinely driven at highway speeds on parkways and the expressway on long Island, and in heavy traffic so it was driven aggressively enough at operating temperature to burn off moisture. Not driving it hard meant not winding out every gear to the max, or downshifting a lot to slow down as a lot of folks drive these cars. I do agree with the acid and dissimilar metal theories presented here, and I think that's what occurred when the engine was not being used and stored in the garage. |
|
| Back to top |
|
|
67rustavenger
Samba Member
Joined: February 24, 2015
Posts: 11337
Location: Oregon
|
| Posted: Tue Oct 14, 2025 6:55 am Post subject: Re: Case sump rot |
|
|
I have two spare engines here in Oregon. I store them on furniture dollies in my garage without oil in the crankcases.
Two weeks ago I tore one down for a camshaft swap. The lower case looked to be in great condition without any of the rot seen in the opening post.
I'm not sure if it is a good idea or a bad one to store engines without oil in them but, that's what I do and haven't suffered any ill affects doing so.
YMMV!
_________________
I have learned over the years.
Cheap parts are gonna disappoint you.
Buy Once, Cry Once!
There's never enough time to do it right the first time. But there's always enough time to do it thrice.
GFY's Xevin and VW_Jimbo!
2003 Astrovan? GFYS again, Xevin! 
Don't let your bad ideas remain, ideas! |
|
| Back to top |
|
|
oprn
Samba Member
Joined: November 13, 2016
Posts: 15015
Location: Western Canada
|
| Posted: Tue Oct 14, 2025 8:32 am Post subject: Re: Case sump rot |
|
|
I am leaning toward stored with new oil but stored with no oil might be ok too.
_________________
Our cars get old, we get old but driving an old VW never gets old! |
|
| Back to top |
|
|
U&I
Samba Member
Joined: July 09, 2024
Posts: 86
Location: Oregon
|
| Posted: Tue Oct 14, 2025 12:36 pm Post subject: Re: Case sump rot |
|
|
The case that I pictured was a fresh uninstalled engine sitting on the floor boards of a Baja without oil and the strainer and cover plate had not been installed, the corrosion was not limited to the bottom either, the case was painted and that did help in the areas where the paint stuck, not so much where it wasn't.
Another point on the anode rods, if there is a high mineral content in the water the wrong anode will smell like rotten eggs, sulfur.
|
|
| Back to top |
|
|
|
