Lotus Elan

Oil spraying from dipstick tube

PostPost by: Andy Hamblin » Tue Mar 17, 2020 4:29 pm

need your help guys, after fixing a couple of oil leaks in other places, there is now a lot of oil being sprayed out of the dipstick tube. A couple of questions, besides the obvious one:

1. Am I right in thinking the dipstick itself doesn't or shouldn't have a seal on?

2. Can anyone tell me what decent pressure reading a compression test should show? (if worn rings, perhaps too much pressure in bottom end was my thinking)

3 and now the obvious question - what else should I be looking at to stop the oil spraying out? Its not a small amount - at 2k rpm, there's a puddle on the floor after a couple of minutes.

4 failing all else, would a rubber boot (spark plug cap?) over the tube or heat shrink actually on the tube as I have seen suggested here be acceptable in your opinion?

Thanks, any help much appreciated.
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PostPost by: billwill » Tue Mar 17, 2020 5:50 pm

Spark plug cap on the dipstick usually does the trick.
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PostPost by: Andy Hamblin » Tue Mar 17, 2020 6:17 pm

billwill wrote:Spark plug cap on the dipstick usually does the trick.


Is this a common problem? what causes it?
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PostPost by: RichC » Tue Mar 17, 2020 7:19 pm

maybe its worth checking your crankcase breather tube which should vent from cylinder head just behind the carburettors to your airbox .
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PostPost by: oldelanman » Tue Mar 17, 2020 7:26 pm

Andy,
Am I right in thinking the dipstick itself doesn't or shouldn't have a seal on?


The dipstick did not originally have any form of seal and is prone to rattling about in the tube and allowing some escape of oil mist. I can confirm that heat shrink tubing applied to the dipstick was effective in curing both these issues for me and others have had similar success using a spark plug boot, but your leak does sound excessive and may not be cured this way. You need to identify and rectify the cause of the high crankcase pressure.

and now the obvious question - what else should I be looking at to stop the oil spraying out?


If you haven't already done so I would suggest you check that the crankcase breather is not partially or completely blocked. That would cause excessive crankcase pressure which could lead to oil blowing out of the dipstick tube.

In case you aren't familiar with the set-up ... on the intake side of the engine there is a rubber tube between the underside of the cylinder head and the fuel pump mounting boss on the cylinder block ..this may have deteriorated and partially collapsed. There is also a pipe between the cylinder head and the intake airbox and this has a wire mesh flame trap inside it which may also have become blocked.

Edit: Rich just beat me to it ! :wink:
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PostPost by: Andy Hamblin » Tue Mar 17, 2020 9:17 pm

Thanks chaps, that's given me a couple of things to try.
Cheers,
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PostPost by: billwill » Wed Mar 18, 2020 1:23 pm

In respect of pressure it is the small pipe at the rear of the carburettors (that goes from the engine block to the airbox) that releases the pressure. As mentioned above it has a wire filter inside which can get blocked.

The original elans had just an open long pipe there that vented to atmosphere down near the bell housing. Any oil vapour that condensed there used to drip on the road.

What most Lotus twin-cam owners don't realise is that the hole in the block just above the fuel pump is where the crankcase breather system used to fit on the original Ford engine. this was a pipe wit a chambers at the top. oil vapour would go up the tube condense there and trickle back down into the sump. There was a vent on the top of the top chamber.

Image

Lotus built that upper chamber into the head instead (It is a separate chamber) and fitted a largish conical rubber tube between that built in chamber and the original hole. So that conical pipe serves to drain the condensed oil back into the sump. The small quantity of vapour that does not condense is passed via a flame filter to the air box, where it get drawn into the firing chambers and burned.

Image


{ it took me a long time to realise that that portion of the head is a separate chamber, it was only when I saw some photos of prototype heads without the chamber, that I realised it is distinct. }
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PostPost by: Grizzly » Wed Mar 18, 2020 3:52 pm

Do you have the correct dip stick installed? the only time i've seen oil pushed out of the dip stick tube in liquid form (rather than a fine mist) is when some one had mistakenly used the wrong dipstick and overfilled the engine with oil.

I see 200psi per pot on a compression test with the throttles open (engine warm)..... try it warm / dry and then repeat with a few drops of oil down the plug holes and see if there is a difference. Usually your looking for differences between wet - dry and between each pot.
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PostPost by: Andy Hamblin » Wed Mar 18, 2020 4:26 pm

Grizzly wrote:Do you have the correct dip stick installed? the only time i've seen oil pushed out of the dip stick tube in liquid form (rather than a fine mist) is when some one had mistakenly used the wrong dipstick and overfilled the engine with oil.

I see 200psi per pot on a compression test with the throttles open (engine warm)..... try it warm / dry and then repeat with a few drops of oil down the plug holes and see if there is a difference. Usually your looking for differences between wet - dry and between each pot.


Thanks for that.

Just under 4 litres of fresh 20W50 mineral oil (and a new filter) was put in which just under the is the recommended capacity so it isn't overfilled. Hesitant to top it up to the recommended capacity until it stops blowing out again!

Compression test showed 170/165/160/175 (dry)
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PostPost by: 1owner69Elan » Wed Mar 18, 2020 7:39 pm

Not sure this helps you at this point, but my engine, when rebuilt, incorporated an o-ring end knob on a modern flexible spring-steel dipstick. No leaks. No rattling. Something to perhaps consider when doing a rebuild.
IMG_4441.jpeg and
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PostPost by: englishmaninwales » Wed Mar 18, 2020 7:51 pm

Grizzly wrote:Do you have the correct dip stick installed? the only time i've seen oil pushed out of the dip stick tube in liquid form (rather than a fine mist) is when some one had mistakenly used the wrong dipstick and overfilled the engine with oil.

I see 200psi per pot on a compression test with the throttles open (engine warm)..... try it warm / dry and then repeat with a few drops of oil down the plug holes and see if there is a difference. Usually your looking for differences between wet - dry and between each pot.


I see same pressures at 195 psi per cylinder under same conditions (standard compression engine).
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PostPost by: Andy Hamblin » Wed Mar 18, 2020 7:57 pm

1owner69Elan wrote:Not sure this helps you at this point, but my engine, when rebuilt, incorporated an o-ring end knob on a modern flexible spring-steel dipstick. No leaks. No rattling. Something to perhaps consider when doing a rebuild.
IMG_4441.jpeg


Hmm.. I'd like to find the cause of the high crankcase pressure before just plugging it up, but when that's fixed I like the idea of that arrangement. Where would I get one like that?

Cheers
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PostPost by: 1owner69Elan » Wed Mar 18, 2020 8:07 pm

The knurled knob with O-ring was custom machined and connected to a generic dipstick. Might be able to get another one made by the engine builder. Now retired but does still work on projects.

Not an off-the-shelf solution I am afraid.
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PostPost by: Andy Hamblin » Wed Mar 18, 2020 8:14 pm

1owner69Elan wrote:The knurled knob with O-ring was custom machined and connected to a generic dipstick. Might be able to get another one made by the engine builder. Now retired but does still work on projects.

Not an off-the-shelf solution I am afraid.


Not to worry. I don't think it would be too difficult to fabricate something similar. Thanks for the idea.
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PostPost by: webbslinger » Thu Mar 19, 2020 4:12 pm

Andy,
Check the vent, but I think these engines can lose a lot of oil out of an unsealed dipstick tube regardless. I recently made an "o" ring dipstick mod and my engine is so absolutely bone dry now it is almost weird. Nothing on the garage floor now at all. Previously I assumed that all the drips were from several sources but apparently that wasn't the case here. I've driven 150 miles since the swap with no measurable oil use so I think the loss through the dipstick tube was significant.
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