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Removing the drain tube fron the rear mains cap.


Jedi Hopeful
I'm in the process of re-building a 3000 engine, and having read somewhere on this forum that the removal of the drain tube from the rear main cap would increase the flow of oil in the area of the rear scroll or after market rear seal, thus reducing the oil loss through the rear seal.

Well not being too sure if this was correct I set up the rear mains cap in the vice, glued between two scrap pieces of plastic. I then pored 5 qts of 20/50 through the cap and timed it. 3 minutes 33 seconds. Did the same with the drain tube removed, 3 minutes and 23 seconds.

If the removal of the drain tube does actually increase the flow, I suggest that when fitted the oil level in the oil pan is more likely restricting the flow leaving the drain tube. May be,, just shortening the tube so the oil exits above the oil level in the oil pan would do the trick?


Any thoughts ?


  • Hly rear main cap.jpg
    Hly rear main cap.jpg
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Jedi Warrior
Why would you want to alter the automatic undercarriage lubricating and rust proof system that was thoughtfully designed into these wonderful cars? The little puddle of oil on your garage floor is a British indicator gauge telling you the system is fuctioning properly! It's one of the factory standard options listed on our Heritage certificates if I remember correctly.


Jedi Warrior
Country flag
@busybrit, great test, thanks for the info. A time difference of only 10 seconds for five quarts? I never bought into the 'remove the tube' school of thought and this seems to confirm what I always thought. There may be some advantage to shortening it to just above the oil level, but what gain is there really? All the other bearings simply drain w/no tube to direct the flow so why need one there? Bottom line is tube or no-tube shouldn't really matter as long as it is clear to drain (not clogged with sludge).
I have always run the tube (no reason except that's the way the factory did it) and have found that with an aftermarket split seal I have very minimal leakage. I think the installation of the seal is most critical - it must be accurately centered around the crank.
And, if you are parking on a steep slope, have the nose pointed downhill not up.

Healey 100

Jedi Warrior
The drain tube on the 3000 is enormous compared to the much smaller, approximately 5/16 ID tube on the 100. I like the experiment busybrit did, but I think the flow difference with and without tube would be way different for the 100. My own experience showing the benefit of removing the tube was on my 100. I would not expect removing the tube to have much effect on the 6 cylinder cars.


Jedi Warrior
Country flag
Here's my take on it. First, there is no rear main seal. There is a scroll on the crank that directs the oil back into the engine when the engine is running. It is only with the engine off that the oil leaks out the back. Secondly, the length of the drain tube is irrelevant. When the engine is running there is a hurricane going on in the sump with the oil wrapped around the crankshaft, splashing oil up into the cylinder walls, pumping oil up into the rockers, and the end of the tube is always exposed. Thirdly, the large circular cavity that is cast into the rear main bearing cap is what the tube drains back into the oil pan. My conclusion is that shortening the tube, on a 6 cylinder 3000 is a waste of time. It won't hurt anything, but it won't make a difference. And it won't have any effect on the amount of oil leaking onto your garage floor.
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