230SLs & 250SLs - Leaking Red Oil Cap on Left Side of Motor

[Cole]

Hi,

Have any of you run into a leaking issue with this red oil cap on the left side of 230SL and 250SL motors?
Please see pictures.
Why is it even there? They deleted it on the 280SLs.
We've tried very hard to tighten it by hand as we're lacking the right tool to tighten it.
Any ideas? Could a rubber washer be fitted inside the cap to more easily tighten it?
Also, are there any after market or replacement caps for this red one that be easier to get on there?
Should it just be glued closed with some semi-permanent glue?

Thanks!
Cole

[Paul & Dolly]

Cole,

It is part of the Bosch Fuel Injection pump, 230 and early 250SL have a separate oil supply, and dip stick, the red cap/vent is for this. The  later cars have an integrated oil supply.
There could be a number of reasons for leakage, have ypu had any work done recently to this area ?

Look up FIP or Fuel Injection pump in the Technical manual on this site and all should become clearer.

Good luck

Paul

[Cole]

Hi Paul,

I appreciate your helpful data on this.
Basically all that happened was my mechanic noticed that the too edge of the red cap was cracked on the top edge and leaking. He also had another cap from a 230SL that he tried, but it leaked, possibly because he couldn't get it on tight enough with his hand. So then, he fixed the crack in the original one with really strong glue and put it back on, but it now leaks from the bottom of the cap probably because he hasn't gotten it on tight enough. If we find a good wrench or tool to grab ahold of the red cap and make it really tight, it will probably fix leaking.
Is there a specific wrench or tool that you recommend?
Also, do you think that putting a rubber washer inside the top of the cap would help screw it on tighter?

Thanks!
Cole

[BobH]

Hello Cole, as far as i know there should be no oil at the level of the cap, so i don't think the cap needs sealing or overtightening, you may damage it

If the oil is high enough to leak from the cap, it could be getting mixed with fuel, due to an internal seal leaking, or it may just be overfilled

Have a read on everything written when you search as Paul suggests

I found these posts

https://www.sl113.org/forums/index.php?topic=4199.0

https://www.sl113.org/forums/index.php?topic=7816.0

I would check the oil level, and if it hasn't been changed recently, syphon it all out and start again, so you know the level is correct, and then monitor it for a while to see if the level rises again

[rwmastel]

Yes, what Bob said.

And, how much tightening do you think a repaired piece of plastic can handle?  If this is just a vent, I'm sure it is not engineered to be screwed on to "lug bolt tightness" with a wrench!

[mazmonza]

Mine is metal I assume it is original.
It is not just a vent but also the oil filler hole

[rwmastel]

Yeah, that's metal and Cole's looks plastic.  I didn't know it was the oil fill access.  I think I filled mine through the dip stick tube in the past.  PITA, this would be much easier.

[Paul & Dolly]

Hi Cole

Here are two pictures of the dipstick on the early pumps.
My pump has the Red plastic vent cap, and I painted the dipstick top Yellow as it is hard to see.

I made an easier to use dipstick from a cable tie, and use a Hypodermic syringe to suck out the oil.
I think Hans said a full charge is 250ml.

Good luck
Paul

[lagolag]

This is a known issue that was up last a year.
If you get oil leak as described then there is a lekage inside the FIP. The reason is most likely due to old sealings inside, the engine oil is filling up the FIP and oil is pressed out trough the filter. I have the same on mine and I have made a Intermedet solution to retain the oil thats pressed out so I dont get oil spill on the floor until I get my FIP rebuilt.

[Cole]

I appreciate your good feedback, guys!

Paul, I looked at your picture of your dipstick and my pictures above when I posted this topic. My picture shows the dipstick above the red cap, correct?
You said a full amount of oil for the pump is 250ml or about 8 ounces, which isn't very much. How low would the oil level need to be to cause a problem with the pump? How would low oil in the pump show in the motor's performance?

Thanks.
Cole

[Cole]

Pardon, please, but what is a FIP?
Thanks.

[Paul & Dolly]

FIP = Fuel Injection Pump..

[Cole]

More good info!

Lagolag,

In your post you said, "The reason is most likely due to old sealings inside, the engine oil is filling up the FIP and oil is pressed out trough the filter. I have the same on mine and I have made a Intermedet solution to retain the oil thats pressed out so I dont get oil spill on the floor until I get my FIP rebuilt."
When you say "oil is pressed out through the filter". do you mean out through the red cap/vent? What was your intermediate solution to prevent oil from seaping out onto the floor?

Thanks.

[Cole]

Pardon me, guys, if this is sort of an obvious question:

Getting back to Lagolag's point if I understood him correctly, it sounds like the red cap is supposed to leak/vent if the fuel injection pump gets too full, right? I.e., my cap leaking is probably ok as the source of the problem seems to be too much oil getting into the pump that needs to vented through the cap? Correct?
Is the overall solution here that the pump needs to be rebuilt or perhaps just a bad seal or something between the motor and the pump?

Thanks!

[DavidAPease]

Cole,

I think that lagolag misspoke; as BobH said, it's not oil that would be getting into your FIP sump, it's fuel.  I'm sure that gasoline isn't as good a lubricant as oil, so having a sump full of gas is probably a bad thing for your pump.  You can possibly verify this by removing the dip stick and sucking out some fluid to see what's in there.

I'm no expert, but assuming fuel is leaking past the seals, the pump probably needs rebuilding.

             -David

[BobH]

Hello Cole, if fuel is seeping into the sump, you'd smell it on the cap or the dipstick.  The vented cap is designed to vent vapour or air, not excessive oil.  As suggested before, best to syphon all of the oil out, through the dipstick, ascertain whether fuel has been mixing with it, and then refill with the correct amount of engine oil and monitor it for a while.  If you're lucky it may just have been overfilled before.  If the level rises again, it must be fuel contamination, so no choice then but to get the pump overhauled

There is a really good description of how to check the oil level on a post i read, i'll add it when i can find it.  There seems to have been a misunderstanding as to how to read the dipstick, and cars could easily be overfilled

Found it, i'l add this to the tech manual, so it doesn't get lost

https://www.sl113.org/forums/index.php?topic=36455.msg266586#msg266586

[Cole]

Hi Bob,,

I appreciate your getting back to me on this and dealing with my junior level questions.
To recap, I need to:
1. Siphon/drain out the existing old oil from the FIP; I'll probably use the spray tube and handle from a spray container and empty it out as best I can.
2. Add fresh 10 30 oil --abt 250ML (abt 8 ounces) and let sit for a while to settle so I get an accurate dipstick reading that it's full.
3. Should I then drive the car or let it idle or just sit there for part of a day to see if the oil level rises due to gas seeping in?
4. a. If the oil level remains the same, I'm good; if it rises, does that mean that the FIP needs to be rebuilt or should other things be checked?
   b. Could excess oil in the FIP affect the motor's performance?
   c. If there is excess oil in the FIP, is it expected that it will be released through the red cap/vent? In which case, oil seeping out of the red cap is ok, right?
   d. Is it possible that the red cap may seep oil even if the oil isn't too high? In which case, any oil seeping out is ok and leave the cap alone? I'm focusing on this because we thought that any oil seeping out into the motor and floor was a negative and needed to be stopped.

Thanks!
Cole

[Paul & Dolly]

Cole,

It is really difficult to get an accurate reading on the dipstick, which is also not so easy to remove continually to check the level, and easily dropped !
I would advise you to make one from a cable tie, as per my photo, before you start...it will make your life easier.
Also the hypodermic is simple to extract the oil, and you can measure and see what comes out.

Paul

[BobH]

Hello Cole, i'm no expert, i just know what i've read and what i've experienced on my own car

This is the excerpt from the post i i added earlier, from Blackforest, who rebuilds these pumps, so a real expert!

For the above concern for Magruder, the easiest thing to do is simply remove the dipstick and let the oil drain out.
Then reinstall the dipstick (some more oil will ooze out) and drive the car a few miles.
Park the car and remove the dipstick.
No oil comes out? Reinstall dipstick and drive 10-20 miles and recheck.
This will allow you to determine how bad the o-ring leakage is.
If it turns out to be minimal and a rebuild is not in the budget, then suck out the oil completely and fill with fresh.

I would set the oil level a little low, as it will overfill regardless.
The oil level is set by placing the dipstick in the recess only, NOT screwing it in.

In answer your other questions, again, i'm no expert, but common sense dictates:

4. a. If the oil level remains the same, I'm good; if it rises, does that mean that the FIP needs to be rebuilt or should other things be checked? - i think if excess oil or fuel is migrating in, poor seals can be the only reason, where else could oil or fuel be coming from?
   b. Could excess oil in the FIP affect the motor's performance? - i'm not sure, but excessive oil in the engine can cause considerable problems, so perhaps it's the same for the pump, perhaps too much oil means too much pressure, and as someone else said, if fuel is mixing with the oil, the lubricating quality will be compromised, i'm just guessing here
   c. If there is excess oil in the FIP, is it expected that it will be released through the red cap/vent? In which case, oil seeping out of the red cap is ok, right? - excess oil has to escape from somewhere, and i guess the cap is the only route, so better escaping from there, than building pressure up inside the pump, but still shouldn't be left, it needs investigating
   d. Is it possible that the red cap may seep oil even if the oil isn't too high? In which case, any oil seeping out is ok and leave the cap alone? I'm focusing on this because we thought that any oil seeping out into the motor and floor was a negative and needed to be stopped. - in my opinion, the oil level should not be high enough to seep from the cap, it's there to top the oil up, or change the oil, and to vent vapour or air, my cap is clean and dry, and i expect other owners, with no problems, would say the same

[rwmastel]

   d. Is it possible that the red cap may seep oil even if the oil isn't too high? In which case, any oil seeping out is ok and leave the cap alone? I'm focusing on this because we thought that any oil seeping out into the motor and floor was a negative and needed to be stopped. - in my opinion, the oil level should not be high enough to seep from the cap, it's there to top the oil up, or change the oil, and to vent vapour or air, my cap is clean and dry, and i expect other owners, with no problems, would say the same

My experience:  When I first got my 230SL and learned about this dip stick and oil reservoir, I unscrewed the dip stick and fluid POURED out!  There was no oil coming out of anything at the top of the pump that I recall, but plenty came out the dip stick tube.  I would estimate I had a 10" puddle of oil on the garage floor, and then I had to remove the rest from the pump.  After proper amount of fresh oil was added, I refreshed the oil a couple more times that summer and there was very little increase in oil level.  I then refreshed the oil once every couple of years.  Fuel Injection Pump rebuilds are expensive.

[lagolag]

Cole,
The red cap is filling and venting cap, the FIP could be seen as a small engine with pistons inside and it has a small oil resouvar and it is vented trough the red cap.
The engine is also vented but it Is routed to the inlet. The Internal FIP seals start to Leak with age and the engine oil is pressed into the FIP and when the FIP oil resouvar is full oil is pressed out trough the FIP vent. The engine oil is pressurized by the oil pump.
For sure also some fuel also enters into the FIP as a result of age but then it ought to be good that engine oil is pressed into the pump so the petrol diluted oil is pressed out.

When I recognized this issue on my Pagoda I started with draining the FIP of oil, I pumped out about 700 ml and noticed the engine oilstick was below the mark.

[BobH]

As i understand it, it may have been misunderstood that these early pumps were only lubricated by their own separate oil supply, but they also had an oil line feed from the engine, they didn't just have their own oil reservoir.  Hence, if the seals fail, engine oil, and fuel can migrate into the other part of the pump, into the reservoir? causing the overfill, with nowhere to escape, apart from the filler/vent cap

Later pumps lubricated only from the engine oil, had an oil return route and no filler/vent cap to leak from. There's a clearer description in Pagoda Notes, worth reading

This is just my understanding

[Cole]

Thanks for all your great feedback, guys!
Per one of BobH's points above, I noticed today that my 250SL injection pump does not have a dipstick, but does have the red cap/vent. And the cap does leak, though I don't know why.

Cheers,
Cole

[BobH]

Hello, as far as i know if the pump has a filler/vent cap, then it must have a dipstick.  Later pumps without a dipstick don't need a filler cap

The dipstick can be hard to find, it's towards the bottom of the pump and should have a screw head, with a T bar

Have a look on the technical manual, or on here for some pictures

https://www.sl113.org/forums/index.php?topic=26563.msg190027#msg190027

[Cole]

Hi,

I have a picture of my injector pump in my first starting post above. I looked it over on the car again today, but didn't see it. My car was built in Sept '67; it appears that the pagoda guys at the factory may have elected to leave the red vent cap as the last vestige of the former independent oil sovereign before going to the integrated oil union in the 280SLs... ?