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MG MGB Technical - Changed oil - now slow to pick up pressure

Hi,

Following on from my thread about using 15w/40 oil in my '66 GT, I've now got a worryingly slow pick up of oil pressure on start up after the car's been standing overnight. The engine's always picked up to 50psi almost straight away after starting, but after putting 15w/40 Castrol GTX in last weekend with a new Champion C102 filter (same as always) it seems to take an age. Start up - oil pressure is zero for 4 or 5 seconds, then flies up to 50psi. After this initial pause, pressure is fine, never falls below 45psi or above 60. Starting after the car's been run and been standing for a couple of hours, pressure builds up nice and fast. It's as if the oil's draining out of the filter overnight, but it never used to and surely 15w/40 is a thicker oil than 20w/50? Any ideas? Oh, and it's not the guage! You can just detect a slight change in engine noise when the pressure goes up from 0 to 50 (when the gauge reads zero there's a very slight rubbing, "whooshing" noise which goes when pressure has built up).

Cheers,
Tim.
Tim Jenner

Tim,

Surely it is the filter draining back overnight. What you say is a perfect description of that particular problem.
Even though you used the same type of filter the anti drain back valve could be faulty.
Do you still have the old filter?
It would be worth trying it. It is not doing the bearings any good to run that long without pressure.
What about trying another brand of filter?
Do you have a filter cross reference catalog?
Other members may be able to suggest better types of oil filter.

Mick
M F Anderson

As Mick says, it is undoubtedly the oil filter, allowing too much oil to drain back into the sump, therefore on start up the oil pressure is sluggish to pick up as it has to travel further/through the filter again.

Two oil changes ago i had the same problems. THe garage that carried this out for me used a Fram Oil Filter. Steve S wrote a very good thread reply on oil changes here (now in archives) he stated that Fram had very poor drain-back facilities and that they should ideally be avoided in preferences for certain other makes with better characteristics, prticularly if you car is used only periodically.

When i was puzzling over why my oil pressure charcteristics had altered when the oil used was the same weight and manufacture as before the change, i remembered Steve's words, went outside looked under the hood and sure enough a Fram Oil filter was there. Next oil change i used a Unipart filter (standard fit in the UK i belive for the B) and have had little problems, except if the car isn't used for say a week or more, then there is often still a delay on build up of pressure.

I dont wish to slag Fram Filters off, just when i used one i did notice a drop in performance in comparison to the makes i used in the oil changes before and after. The point i make is that the oil filter can make a difference to the overall behaviour of your engine.

~PHIL
Phil

Tim. I have used the Mann W 917 oil filter for many years with good results after it was recommended by one of our better posters. As to your question about oil thickness, no, 15-40 is not a thicker oil than 20-50. It is a thinner oil as the lower numbers indicate. The higer the numbers the thicker the oil. Les
Les Bengtson

Thanks for the responses. Two questions - is the anti-drain back valve in the filter itself, or in the base plate? And secondly, if 15w/40 is a thinner oil than 20w/50 (I still confess to being confused about all this viscosity stuff) then could that be to blame?

Thanks,
Tim.
Tim Jenner

Tim, The anti-drainback valve is in the oil filter itself, not in the filter adaptor.
Replacement of the filter alone will probably
solve the problem. I got a five-pack of Unipart
filters here in the U.S., and as Phil states
they work fine.

But 20W50 is the original recommendation for these
cars, I think 15W40 is too thin.
Ronald

Tim. The anti-drain back valve in a part of the oil filter. Hence, there is a chance of a bad one with every new filter installed. However, the relatively low cost of the oil filters, even the premium ones, makes it an easy and cost effective first thing to check. Yes, thinner oil might tend to drain out of the system a little more easily than a thicker oil. Basically, the viscosity index, which are the numbers on the oil bottle, is the measurement of how well an oil flows at a certain temperature. This temperature varies depending on the application of the oil. Thus, 90 weight gear oil flows about like 40 weight engine oil at the same temperatures. Gear oil is measured at something under 300 deg F while motor oil is measured at something under 500 deg. Multi grade oils, such as 15-40 or 20-50 have additives which cause the oil to thicken (flow less readily) as the oil is heated. However, since oil tends to thin (flow more easily) as it is heated, the net effect of the multi grade oils is to have a more uniform set of flow characteristics over the entire operating temperature than a "straight weight" oil. With age, and miles, the multi grade oils loose this ability and act like a thinner oil all the time. This is why it is an excellent idea to change the oil and filter every 3K miles. It should provide all of the multi grade benefits for the entire working life of the oil. The Scions of Lucas website used to have one or more excellent articles on oils. Worth researching. Les
Les Bengtson

Ronald. We were posting at the same time. 20W-50 oil is the most popular. However, the 15W-40 is also a "recommended" oil as is 5W-20. Depends on operating conditions. The factory Driver's Handbook for the later model cars has a chart with several different oils recommended, including the ones noted, based on the ambient air temps to be encountered while driving. Earlier copies of the Driver's Handbook, have a different form of chart, giving oil recommendations by brand of oil. However, the basic recommendations are comparable. For winter driving, when the car is stored in a non-heated garage or outside, the 15W-40 might well be a preferred oil as it will flow better when colder. There were a wide range of oils recommended for use in these engines over the life time of the engine and some of the older recommendations might be worth looking into for certain applications. I believe straight 40 weight might well be superior for hot, summer use than the 20W-50. People who live in snow country, and drive their cars in same, have recommended the synthetic oils based on their better flow characteristics when really cold. Les
Les Bengtson

I know everyone praises the Unipart filter, but the one on my car drains right down in just a few hours while I am in my workplace. I may just have a faulty unit, but I thought I would let you know that Unipart filters aren't always superb.

Mike
Mike Howlett

As a UK comprison, taking into account what Mike says, a friend of mine uses Champion oil filter on his BGT and has had good results. I may try one of these myself on the next change.

The trick i suppose is to find one that suits your engine and its usage, as of course, everyone is different!

~PHIL
Phil

Here's some info that you guys may find interesting
http://minimopar.net/oilfilterstudy.html
I, too have had nothing but trouble with Fram filters. Now I use Motocraft or NAPA
gerry masterman

I concur with Mike Howlett's comments about the unipart filters. The last two I used both resulted in slow oil pressure build up after the car has stood for several hours. I just had the filter changed by a local garage, not sure of the make, but even when I leave the car over the weekend (Friday pm to Mon am) the pressure starts building up within a second or two.
So my conclusion is that it's just luck of the draw with the majority of brands. Has someone come up with an adapter to hang the filter the other way up yet? Sounds like the best solution to me.
Phil B

Phil,

I agree, the only proper solution to oil filter drain back is to have the spin on filter fitted the correct way up.
I have fitted many spin on filter adaptors and have never had the filter "upside down".
It may be a bit more difficult to change the filter but it is worth the effort.
They are sold by Moss USA, see website:
http://www.mossmotors.com
It is listed under "MGB" then "Maintenance".

Tim,

I have always bought my "correct way up" adaptors from Moss UK.

Mick
M F Anderson

I'm with Mike and Phil B. I went to my local supplier and bought three Unipart filters one time several years ago. Every one of them had a defective drainback valve. When you looked at the valve after removing the filter, you could see it was very wavy -- no way it could seal. Maybe it was just a bad production run, but I've not used a Unipart filter since. After reading the study cited above, I've settled on Purolator PL14670. No slow oil pressure with them!
Rob Edwards

Thanks for the suggestions - I will get hold of another filter and try that. The one I fitted is a Champion C102, the same type I have fitted for the last 4 years with no problems! When I take the filter off, is there a way to check the drainback valve? Can one check the valve on a new filter before installation?

Thanks,
Tim.
Tim Jenner

About all you can do is a visual inspection, unless you want to cut the filter open. When you look at the end of the filter, there's a threaded hole in the middle and a ring of smaller holes around that. The valve is just a rubber flap that closes those smaller holes. On a new filter just look to make sure that: 1. the valve is there, and 2. it looks ok (not wavy, no tears, etc. -- i.e. no obvious defects).

The Purolotar PL14670 is one of their PureOne filters, so it has a silicone rubber flap and seal ring. Theoretically that should be better than the rubber used in the cheaper filters....

I doubt Purolator uses different numbering schemes in the UK, but if they do, the PL14670 is the stock filter for most Volvos from the 1970s through the 1990s....
Rob Edwards

This thread was discussed between 02/03/2003 and 03/03/2003

MG MGB Technical index

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