The Lotus Grand Tourers

I'm about the put the sump back on to my block and the workshop manual mentions a dipstick tube O ring. The parts diagram appears to show this fitted from below, after the dipstick tube upper section has been fitted into the block and tightened in place with a screwed union and collapsible olive. If that's the case it would just slide over the part of the tube that extends below the block, and it would settle against the lower dipstick tube (welded to the sump baffle) which has a flared upper end.

Or have I got it wrong and it goes into the block just below the olive? Either way I can't see it achieving very much, and there wasn't one on there when I stripped the motor.

Cheers

John

You mean part A035 in the cylinder block parts list sketch? It looks to me from the sketch that it should end up surrounded by the flare at the top of the lower tube that's part of the sump baffle, as you say.

Does the upper dipstick tube slide inside the lower tube, so that the ID of the O-ring contacts the upper tube? In which case, as you say, it doesn't seem to do anything useful.

But if the ID of the O-ring is exposed once it's all assembled, I would say that its purpose is to seal against the dipstick itself, preventing oil coming up inside the dipstick tube. So it's only doing anything useful when the dipstick is installed.

It's been too long since my engine rebuild for me to remember how this went together, if there was one present in mine, or if I fitted a new one.

Hi Richard, yes thats the part number and the upper tube can slide into the larger ID lower tube with the flare.

If I fit an O ring to the protruding part of the upper tube, as you say it will just nestle into the flare of the lower tube, there's nothing to compress it like you'd normally expect with an O ring, and it's purpose is a mystery!

If the intention was to seal the dipstick itself, the O ring would have to be squashed into the flare by the upper tube, which means the upper tube would have to fitted very precisely to give the required amount of squish. I can't find any mention of that in the manual, but it makes more sense.

Thanks for your thoughts on the matter. The most worrying aspect of this isn't oil leaks due to the O ring being present or not, the fitted height of the upper tube will determine how far into the sump the dipstick protrudes. If you fit the upper tube too far into the block, the dipstick reading will be wrong!

I may give SJ a call to see if they can clarify, and I'll update the post when I've done some more digging!

Cheers

John

John wrote: Thu Jul 24, 2025 09:56 Hi Richard, yes thats the part number and the upper tube can slide into the larger ID lower tube with the flare.

If I fit an O ring to the protruding part of the upper tube, as you say it will just nestle into the flare of the lower tube, there's nothing to compress it like you'd normally expect with an O ring, and it's purpose is a mystery!

description seems to be" O RING, DIP STICK TUBE on SUMP BAFFEL to BLOCK "

suggest to me it has nothing to do with sealing, but exists to stabilise the bottom end of the dipstick tube to give the seal with the olive a better life
"

Hi Marten

Thanks for your thoughts on this, but that description fits the parts illustration. It appears to show the O ring going on from the sump side, not from the top with the olive. It suggest a seal with the baffle part of the tube, not the upper tube coming through the block.

The workshop manual reminds you to fit a new O ring before bolting the sump back on, but it doesn't say exactly where it goes. Bit vague!

Cheers

John

On checking the engine spec in the workshop manual I discovered that the dipstick upper tube is supposed to protrude 119.5mm from the main bearing panel, so I think that answers my question. I haven't refitted it yet but I reckon that the upper tube won't protrude into the sump at all if fitted to the specified height, and a correctly sized O ring will be squished up against the lower surface of the main bearing panel by the flared end of the lower dipstick tube (the one welded to the sump baffle).

It all makes sense now! The dipstick will hold the O ring in place when I assemble tha baffle and sump.

Cheers

John

Baffled again! With the top of the dipstick tube set at 119.5mm from the main bearing panel, the tube does extend into the lower flared tube, so the O ring has no contact at all with the dipstick itself.

It just nestles in the flare of the lower pipe, having been pushed over the end of the upper pipe. It's not compressed like a normal O ring. Doesn't appear to do anything important.

That 119.5mm dimension is important however, glad I found that. If the upper tube isn't set correctly the dipstick readings will be wrong.

Cheers

John

Being a stickler for correct words, an engineering trait for accuracy, I believe this post refers to the Oil Pick-up Pipe.
The dipstick is that element externally on the side of the engine which is to measure the oil level in the sump.
Sorry for being pedantic, but it can avoid confusion.

Dave the cog

Hi Dave

No, definitely the oil dipstick tube! The upper section sticks out of the block and holds the dipstick, and the lower section is welded to the sump baffle plate. And there's an O ring for good measure.

The upper tube is locked into place with a screwed nut and a brass olive, and when fitting a new olive it's possible to set the tube height before tightening the nut. Accuracy of the dipstick readings depends on the height of the upper dipstick tube (protrusion from main bearing panel, quoted in the service notes as 119.5mm).

The oil pickup pipe also uses an olive, but thats a bigger plastic (nylon?) thing.

Cheers

John

Hi John. I can now see what you mean and agree it is a dipstick.
When working on the engine I normally remove that part of the external dipstick protruding from the block, mainly to avoid bending when lifting strops take load.
I was not aware that there are crushable olives there,
I appreciate your correction.

Just to add a note, on the oil pickup pipe, when this is re-installed it is to be impressed the care on correctly locating and sealing the plastic olive. Any misfit can cause oil pressure loss and priming on engine start-up.


Dave the cog.

Hi Dave

Thanks, no worries. I had to straighten the upper dipstick tube on mine, as you say probably got bent when the engine was lifted at some point.

You're right about the oil pick up tube, the olive needs to be in good shape and the union correctly tightened, otherwise the oil pressure may not be to spec.

Cheers

John