Cabin Fumes / Oil Filler Cap

[Gorpon73]

Hello,

I've recently went through hunting down the dreaded coupe cabin fumes wormhole.

I've eliminated it for the most part and I believe I've traced this down any remaining smell to oil dripping out of the oil filler cap run-off tube onto the exhaust. My question is this. I've read a number of solutions for this. Thoroughly sealing the cap, running the tube back to the block, running the tube under the car, installing a catch-can.

Is there any drawback to just eliminating the run-off/venting and ensuring the cap fully seals? I do have the breather in place and sealed to the airbox.

For reference, if it helps anyone else, to fully eliminate the cabin fumes I had to seal/eliminate the following:

- Sealed rear cabin bulkhead using plastic and vent tape.
- Sealed shock strut access holes with rubber grommets and tape.
- Sealed frame access holes in the front of the trunk.
- Sealed the space around the gas tank drain hole.
- Sealed the engine breather hose on block and air filter housing.
- Sealed exhaust joints with RTV Red.
- Sealed shifter boot using plastic and tape.
- Extend exhaust outlet well beyond rear bumper (questionably road legal).
- Seal holes surrounding wires running through the engine bay to the cabin using silicone.
- Eliminated dripping from transmission case down to the exhaust via the exhaust bracket.

Thanks

[gherlt]

>Extend exhaust outlet well beyond rear bumper (questionably road legal).
My original S4 exhaust (the one with two small tubes) go well beyond the rear bumber (~15cm)
As far as I understand that is original, so ... if legal at the time, it is legal now.
But I cannot imagine those fumes coming into the cabin ...

Back to your issue, it is the first time I hear of " oil filler cap run-off tube",
never seen this. Is this a "Federal"/US item ? Could you post a picture ?

You certainly seem to have a problem with fumes, I understand it, my wife complains about the smell after 10 min driving. On longer legs with hood up it is annoying

[Gorpon73]

Yes, my fumes are at were extremely bad.

After going through all the seals, I noticed that it was particularly bad the first few drives of the year and suspected it was all the crud that leaked out over the winter onto the exhaust. After sealing everything and ensure all the leaks are away from the exhaust it was better. Not perfect, but live-able.

Its a Federal car, but I'm certain the cap is not original. It's basically just a hole with an elbow fitting screwed in and a rubber tube attached. I presume it was like this because the cap leaked. It pukes a surprising quantity of oil over a 100 mile trip...

[mbell]

I am not aware of federal cars coming with a different cap. As far as I know they all came with the same type of cap, as shown here:
viewtopic.php?t=27341&p=183492

It maybe a previous owner changed it to aid crank case breathing or something. I suggest you look at changing it for more standard item without the extra breather. Also common to fit a deflector plate under it to stop oil being splashed on the underside of the oil cap and then blown out of the engine.

[Gorpon73]

Thanks. I did see the ones at Burton and thought about getting a new one.

I'd love to do the deflector plate, but may under the cam covers for a few more years at this rate!

[oldelanman]

Do you have the foam sealing strip in place along the rear edge of the bonnet aperture ? Without that engine bay fumes will be drawn into the heater intake and thus into the cockpit.

[Andy8421]

Do you have the foam sealing strip in place along the rear edge of the bonnet aperture ? Without that engine bay fumes will be drawn into the heater intake and thus into the cockpit.

Was going to mention the same thing. Driving my convertible with the hood up was an upleasant stinky experience until I put the foam strip in place.
The OP's filler cap sounds like a home-brew setup. There must have been a reason to put it in place - perhaps the breather tube was blocked, or the engine has significant blow-by. A pipe as described will always blow out oil, there needs to be a mechanism to separate the oil droplets and mist from the gas stream. Lotus have their 'velocity drop chamber' cast onto the head to do this, the separated oil drains back into the sump. Without this, you will inevitably lose oil out the breather.

[gjz30075]

That strip of foam really works. I've got a few open holes in the firewall of my S3 Coup and
recently went on a drive with the oil cap not fully seated, unknowingly. I never smelled
the oil but certainly saw a mess when I stopped and popped the bonnet just to check things.
I guess it depends on where the oil leaks out.

[pharriso]

I've eliminated it for the most part and I believe I've traced this down any remaining smell to oil dripping out of the oil filler cap run-off tube onto the exhaust. My question is this. I've read a number of solutions for this. Thoroughly sealing the cap, running the tube back to the block, running the tube under the car, installing a catch-can.

Is there any drawback to just eliminating the run-off/venting and ensuring the cap fully seals? I do have the breather in place and sealed to the airbox.............
Thanks

I don't think that you are talking about the "Oil Filler Cap" & calling it that that has confused everyone... The Oil filler cap is this:

What I think you are talking about is the Oil Breather pipe from the cylinder head air box to the intake plenum:

There is a Rubber grommet where the breather pipe fits into the cylinder head; Can you confirm this is what you are talking about?

Early cars did not have this arrangement, they just had an elbow attached to a length of rubber hose which went below the car... commonly referred to as a "Road Oiler"

What model / year is your car?

[Gorpon73]

No, I am not referring here to the breather tube. I have a new breather tube and grommets on both ends at the block and air box.

My oil filler cap has a metal elbow inserted with a tube extending down through the engine bay to the bottom of the car.

I do have the foam on the near edge of the hood and it does seem to seal well. When I use my fan it does not blow stinky air into the cabin (miraculously the fan still works).

The smell is nearly completely gone, so not overly concerned on that. I'd just like to confirm that if my breather hose is in place, I can eliminate the filler cap tube (provided I can seal sufficiently to prevent leaks).

[pharriso]

My oil filler cap has a metal elbow inserted with a tube extending down through the engine bay to the bottom of the car.....
I'd just like to confirm that if my breather hose is in place, I can eliminate the filler cap tube (provided I can seal sufficiently to prevent leaks).

How strange!

If the Oil Filer cap is leaking you can replace the cap seal; you can also add an oil deflector plate - see https://lotuselan.net/forums/viewtopic.php?f=39&t=49862.

[Andy8421]

No, I am not referring here to the breather tube. I have a new breather tube and grommets on both ends at the block and air box.

My oil filler cap has a metal elbow inserted with a tube extending down through the engine bay to the bottom of the car.

I do have the foam on the near edge of the hood and it does seem to seal well. When I use my fan it does not blow stinky air into the cabin (miraculously the fan still works).

The smell is nearly completely gone, so not overly concerned on that. I'd just like to confirm that if my breather hose is in place, I can eliminate the filler cap tube (provided I can seal sufficiently to prevent leaks).

If you could post a picture, that would be great. It is always interesting to see the 'improvements' previous owners have made. In the days before phone cameras, I worked on many a bodged car. My favourite was a MG Midget where the front scuttle was held together by a flattened out Cadbury's chocolate drink can riveted behind it. It would have been great to have pictures to record these things.

[Gorpon73]

Yeah, can't say I haven't had a number of "why would you do it like that" moments with the heaps of junk I've had through the years.

Here is this beauty. Oddly, the rest of the car was restored to a quite good standard. Not sure how this played in.

[Andy8421]

Good grief, haven't see one of those before. I think we can all agree that isn't a standard fitting.

Question remains why it was done.

[RobertMaulden]

I have actually seen something like that before, only the fitting in the filler cap was connected by a tube to a catch tank.

It's a cheapskate way of venting the top end of the engine (as opposed to machining a fitting into the front of the cam cover - where it normally is)