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MG MGB Technical - Inverted filter pressure problems

G'day. I have read all the threads regarding the problems with oil pressure being slow to respond on start up, especially after a few days of not using the car. I have had this problem for months and have used 3 different makes of filter, all with non-return valves.

A few days ago I decided to have another go a fixing the problem as it was taking anything up to 20 seconds to get the oil pressure to register. I took the filter off and it was completely empty. I took the inverted fitting off and tested both of them.

I filled the filter with 10W fork oil (as it is very thin and should leak faster than normal oil)and sealed of the centre threaded hole. After 2 hours with the filter inverted there was no sign of a leak. I filled the centre tube of the fitting with petrol and sealed off the outlets. After 2 hours no sign of a leak.

I came to the conclusion that the only possible way of losing all the oil out of the filter must be through the threaded portion, so I put some "gasket goo" on the thread and re-assembled the whole lot. I now get 60PSI after 3 to 4 seconds.

If you are having problems it might just be worth a try.

Tony
Tony Oliver

Interesting. Do the threads on the filter head look excessively worn or in some way damaged? It might be time to consider replacing it!
Rob Edwards

Interesting indeed. Might explain why some time ago one person complained that he was getting instant drain-back with multiple Unipart and Champion filters whereas I wasn't. I've been making some notes on time to get pressure with different filters over the years. Can't find the Champion and Halfords figures at the moment, but I know I paid extra for some Fram filters from a well-known organisation said to contain an improved anti-drain-back valve and they were worse after 12 months. Then tried a Volvo, which is about 50% dearer, but that was better than all the previous taking 10 secs after standing 2 weeks, that is firing up in 3-4 secs. Currently I have a K&N Gold which when new was slightly longer than the 12 month old Volvo, and double the price, so I shan't be getting that again. It has been consistent over 12 months though.

Not sure I want gasket goo in my lubrication system, though.
Paul Hunt

Rob. The unit was second hand and I didn't really check the threads. I will next time the filter is replaced. Perhaps it is a fault with the filter threads and not the thread on the unit.

Paul, I agree with you about the goo. The filter is up for replacement shortly and I was considering using plumbers thread tape instead of the goo.

Tony
Tony Oliver

Tony,

I recall the background discussions on your experiences with oil filter adaptors.

Given you are correct in the assumption that the only place you could be losing control of the oil pressure build-up (20 seconds sounds excessive) is through the threads of the filter to adaptor connection, Rob has made a good point. The adaptor threads could be damaged from wear.

Alternatively, you may have a mismatch of threads between the adaptor and filter. I had discussed thread issues in a contribution I made to a post of yours when you were looking for an alternative adaptor to the one that had failed. There is a similarity between (from memory) 1/2"BSP and 3/4UNF That can be difficult to pick up visually. I think the thread counts match but the thread pitch differs. If you, or a PO, has screwed one down on the other I would expect at least the thread points to be damaged.

Whether that damage is enough, at this point or at some time in the future after additional filter replacements, to compromise the integrity of the threads ability to hold I don't know. However, in a system building 60plus PSI I would be wary of a filter 'blowing' off. I suggest you check the threads carefully (re-read my earlier posting - it contains some thread details on the adaptor and filters commonly available here) to at least eliminate that possibility.

It would be dreadful to have a repeat of your earlier experience.

Regards
Roger

Roger T

Thanks Roger. All I can say is that when I removed the filter to check out the problem it was totally empty. There are only two ways for all the oil to get out that I can see, the non-return valve or the thread.

20 seconds was the figure taken with a larger diameter filter than the previous ones but it was never less than 10 seconds, and this was with a new oil pump. I assume it took that long to fill the filter before the oil pressure started to register.

I take your point about the thread. I'm not sure which one the filter is, I just got one that was recommended by various contributors.

I am very VERY happy to report that after 3 days of non use the oil pressure came up in about 3 seconds.


Tony
Tony Oliver

Tony,

On filter threads, Ryco filters stamp the thread dimension in the metal face that seals to the adapter. I have seen the same thread stamps on other filter makes as well.

If the adapter you have is, like mine, from an OZ Mariner, it will be 1/2"BSP thread. The only filter I am aware of with that thread (and both drainback valve and the bypass facility required with that adapter) is the RYCO Z23.

If you have another type of apapter the thread might be BSP (if of Leyland type of the period) or, and possibly more likely, especially if of a later period, 3/4" UNF. Of course it is possible a previous owner has had a thread fitting made to a unique filter thread size as well. In the latter case, or if of a Japanese vehicle eg Datsun, it could be a metric size.

If my memory serves me, a BSP thread measure gives the INTERNAL diameter of the fitting (ie 1/2"BSP is a 1/2" internal diameter pipe). UNF thread measures give the EXTERNAL diameter of the fitting, including the thread itself.

They do not match as a fitting pair, one would require a degree of forcing to drive home on the other and that will cause damage and eventual loss of integrity in the security of the fitting. It would be worth while checking that you do have the correct match.

If your adapter has the removable thread fitting (eg that for the Mariner does, it is 1/2"BSP both sides), and the filter fitting threads are damaged, you can have a machine shop make up another thread fitting - you would not have to remove/replace the adapter unit itself.

Regards
Roger
Roger T

Thanks Roger. I can't say for sure but I think the fitting was off an American MGB. I got it through eBay.

I have never had to force the filter on at any stage. The first time I used it it went on very easily. Thats not to say the threads were not damaged before I got it.

I'll check the filter and threads carefully when I remove for the upcomming oil change.

Tony
Tony Oliver

Ah! Our late-car friends then will be able to tell you what thread you have on the adapter. If lucky you will have something like a 3/4"UNF or thereabouts - for which there will be a greater number of filter choices available.
Regards
Roger
Roger T

Roger. It is the 3/4x16 UNF thread. To date I have tried a Coopers Z27A which has been superceded by the Z73, a Valvoline Z9, a Ryco Z38 and the current Ryco Z89A.

I guess the most likely explanation is that the PO damaged the threads in some way or, as you suggested, had the thread changed. Next oil change will see the fitting removed again and the thread type identified by my local mechanic.

This morning I started the engine after about 20 hours no use and got oil pressure before the engine fired!

Cheers
Tony
Tony Oliver

This thread was discussed between 28/03/2009 and 01/04/2009

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