I know there is a lot here on this forum on the common problem with the E500E of the "moisture in the distributor cap" problem that can cause the obvious problems that it does (uneven idling, loss of some power, running a little rough). I think I have read most everything here on this issue, as well as other forums and lots of stuff on-line.
My usage pattern for my car almost guaranteed the problem would arise. Specifically, in my case, let the car sit for 2 weeks, drive it for 15-20 mins, let it sit for 15+ minutes and then go try to drive it again. It seems like I could trigger this problem each time by just doing that usage pattern.
In any case I had read a lot on this problem over last few years and had seen various proposed solutions that seemed to have worked for others i.e. simply putting in new distributor cap, rotors, insulators; OR drilling a 4mm hole in the distributor cap so more air can flow though, or use a dremel to cut additional slots (same idea as 4mm hole); OR put a coating on the caps to try to inhibit moisture buildup; OR a combination of the above.
I know there has been discussion/debate on the source of the moisture. I think I have finally solved the problem I was experiencing and also have an opinion on the origin of the moisture problem. My goal was to try to eliminate the origin of the problem since I had replaced the distributor cap and rotors before and that seemed to have worked for a while, but then the problem eventually comes back. I started to think "it's an inherent design flaw on these cars and you just have to live with it and address it when it comes up" (or change my usage pattern which made it seem especially prone to this issue arising).
In any case here's what I did that I believe finally solved the problem, due to addressing what I believe is the root cause of the problem on these cars. I did a “belts & suspenders” approach (i.e. what others had suggested here) as well as one additional step that I think may be key:
Net: New Distributor Caps, Rotors, Insulators, but with a coating on the inside that Jono uses, plus additional slots he cut in to breathe PLUS removing old camshaft seal and replacing it with two new camshaft seals on each side.
I tried to fix this problem before with new Distributor Caps, Rotors, Insulators. The Distributor Caps and Rotors on my car had only ~1,000 miles and the moisture problem still reared its head so I had no faith that was addressing the root cause (there were supposed to be new insulators put on with the new Distributor Caps and Rotors ~1,000 mile ago, but that was an oversight, so it did not happen). When I replaced them before, they did not have the coating Jono puts on, nor the new slots he cuts in to help with airflow. When I originally put on new Distributor Caps & rotors (not the ones I just put in from Jono, but prior to that, I put in stock ones, with no coating and no extra slots to breathe) it made the problem go away for a while, but then it came back.
Take a look at the picture below of the moisture that was on the backside of the insulators (in front of the camshaft seals) - that is not bubbling of the plastic on the insulators, that is all mositure/water droplets. The car hadn't been driven in 2+ weeks, then driven ~9 miles to my mechanic where it sat in his garage overnight and this is what the back of the insulators looked like. Also, if you don't fix the root cause of the moisture, which I believe is old/worn camshaft seals causing oily mist to build up in the insulator and distributor cap, even with new insulator/cap/rotors your car will run ok for a while but the contact points in the distributor will slowly build up some mositure/corrosion and even though it may seem to run ok, having those contacts wet or with even minimal corrosion, there is no way your engine is operating at 100% of capability.
My mechanic said he was able to fit two camshaft seals on each side as I had asked and it was no problem. Importantly he said something to the effect of: "These could have been the original camshaft seals on the car. Many of these cars may be driving around with 30+ years old camshaft seals, look at the moisture on the back of your old insulators here." (see below)
I suspect worn/old camshaft seals are the root cause of the build-up (which is combined with engine heat, oily mist created by worn seals, differences in temp between outside air and engine). I suspect having extra airflow helps alleviate that problem to a degree, as well as new distributor cap, insulator, rotors, but I don't believe it eliminates the problem 100% and I think the moisture will build-up again, unless you replace the Camshaft Seals (and I suggest putting two on each side vs. factory spec of one).
Now my car feels like it idles like it has just finished the break-in period from the factory, I am really surprised at what a difference this made compared to last time, when just the distributor cap & rotors were just swapped out, last time I tried to address this issue.
I could be 100% wrong - who knows - but my sense from the idle on the car now and me trying to induce the problem again (by replicating same usage pattern over and over again) and not being able to, makes me believe it's finally been solved.
My usage pattern for my car almost guaranteed the problem would arise. Specifically, in my case, let the car sit for 2 weeks, drive it for 15-20 mins, let it sit for 15+ minutes and then go try to drive it again. It seems like I could trigger this problem each time by just doing that usage pattern.
In any case I had read a lot on this problem over last few years and had seen various proposed solutions that seemed to have worked for others i.e. simply putting in new distributor cap, rotors, insulators; OR drilling a 4mm hole in the distributor cap so more air can flow though, or use a dremel to cut additional slots (same idea as 4mm hole); OR put a coating on the caps to try to inhibit moisture buildup; OR a combination of the above.
I know there has been discussion/debate on the source of the moisture. I think I have finally solved the problem I was experiencing and also have an opinion on the origin of the moisture problem. My goal was to try to eliminate the origin of the problem since I had replaced the distributor cap and rotors before and that seemed to have worked for a while, but then the problem eventually comes back. I started to think "it's an inherent design flaw on these cars and you just have to live with it and address it when it comes up" (or change my usage pattern which made it seem especially prone to this issue arising).
In any case here's what I did that I believe finally solved the problem, due to addressing what I believe is the root cause of the problem on these cars. I did a “belts & suspenders” approach (i.e. what others had suggested here) as well as one additional step that I think may be key:
1. I bought Distributor, rotor, insulator from Jono - he put a special coating on the stock Bosch ones - that apparently Mercedes used to have a similar on theirs, but stopped putting that coating on during the period of the 500E/E500 according to Jono, as well he cut in extra slots for air flow.
2. I had new Camshaft seals put on. These seals sit right behind the insulator and were a real pain in the neck to remove according to my mechanic who has been working on MB's for 40+ years (yes I know there is a special tool and he did not have that). The factory spec calls for 1 Camshaft seal on each Camshaft, but there is room for two on each side. I found this on some in a single comment in some obscure post on some place online and I can’t even remember where. Someone tried new Camshaft seals and it solved his problem, no replacing distributor/rotor/insulator (after making sure they are dry of course).
Net: New Distributor Caps, Rotors, Insulators, but with a coating on the inside that Jono uses, plus additional slots he cut in to breathe PLUS removing old camshaft seal and replacing it with two new camshaft seals on each side.
I tried to fix this problem before with new Distributor Caps, Rotors, Insulators. The Distributor Caps and Rotors on my car had only ~1,000 miles and the moisture problem still reared its head so I had no faith that was addressing the root cause (there were supposed to be new insulators put on with the new Distributor Caps and Rotors ~1,000 mile ago, but that was an oversight, so it did not happen). When I replaced them before, they did not have the coating Jono puts on, nor the new slots he cuts in to help with airflow. When I originally put on new Distributor Caps & rotors (not the ones I just put in from Jono, but prior to that, I put in stock ones, with no coating and no extra slots to breathe) it made the problem go away for a while, but then it came back.
Take a look at the picture below of the moisture that was on the backside of the insulators (in front of the camshaft seals) - that is not bubbling of the plastic on the insulators, that is all mositure/water droplets. The car hadn't been driven in 2+ weeks, then driven ~9 miles to my mechanic where it sat in his garage overnight and this is what the back of the insulators looked like. Also, if you don't fix the root cause of the moisture, which I believe is old/worn camshaft seals causing oily mist to build up in the insulator and distributor cap, even with new insulator/cap/rotors your car will run ok for a while but the contact points in the distributor will slowly build up some mositure/corrosion and even though it may seem to run ok, having those contacts wet or with even minimal corrosion, there is no way your engine is operating at 100% of capability.
My mechanic said he was able to fit two camshaft seals on each side as I had asked and it was no problem. Importantly he said something to the effect of: "These could have been the original camshaft seals on the car. Many of these cars may be driving around with 30+ years old camshaft seals, look at the moisture on the back of your old insulators here." (see below)
I suspect worn/old camshaft seals are the root cause of the build-up (which is combined with engine heat, oily mist created by worn seals, differences in temp between outside air and engine). I suspect having extra airflow helps alleviate that problem to a degree, as well as new distributor cap, insulator, rotors, but I don't believe it eliminates the problem 100% and I think the moisture will build-up again, unless you replace the Camshaft Seals (and I suggest putting two on each side vs. factory spec of one).
Now my car feels like it idles like it has just finished the break-in period from the factory, I am really surprised at what a difference this made compared to last time, when just the distributor cap & rotors were just swapped out, last time I tried to address this issue.
I could be 100% wrong - who knows - but my sense from the idle on the car now and me trying to induce the problem again (by replicating same usage pattern over and over again) and not being able to, makes me believe it's finally been solved.
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