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MG MGB GT V8 Factory Originals Technical - Oil change

I've just bought a v8 roadster "minter" . I have had a BGT for 22 years so I know the normal stuff. Just would like what to do about the type of oil to use ,and how often. Engine is a 3.9 rover

regards Ray

10-40 high detergent - your choice make - every 3000miles


Usually Valvoline 20/50 every 3000 but will be trying Magnetec for conventional engines.


I'm using 20w-50 in my 3.9 L MGB as instructed in both Rover SD1 and Range Rover 3.9 shop manual and change with filter every 5000 km (3000 m)
Keith Childs

There seems to be a consensus that the oil & filter should be changed every 3k miles - that's what I do on my B GT V8 and RV8.

As to oil I prefer Duckhams 20/50 - certainly don't waste your money on synthetic or semi-synthetic.

Safety Fast

Nigel Steward

I have had good success with Valvoline 20W50 racing oil in my 1991 Range Rover 3.9 (295,000 miles). Oil and filter changes have been every 3,000 miles.

With synthetic oil, I have been told that I would not get the brown film that I see on the oil fill plug and valve train. Nevertheless, this residual film has not been a problem.

Charles Clarke

I have been waiting to comment on my recent change to Castrol Magnatec. Apparently there are several viscosities available in the UK with someone recommended the higher variant. I checked with Castrol in Oz and the only available here is 10w 40.

I decided to make the change in an effort to minimise the much talked about rattles on startup. I have done a lot of research on prelubers and like the idea but haven't made a move to install one.

My engine is a healthy, rebuilt 3500 with about 5,000 miles travelled. Starting the engine every day or second day is fine, but if I leave it a week or 2 which I often do, then I cringe until the oil pressure is up.

I am sure most of you are familiar with this topic.
Well, I started the motor after 10 days and I was so pleased with how much quieter it was initially.

In this hot climate (40C lately) 10w 40 seems a little thin for an old engine design, but I thought I would give it a try.


I have never had great oil pressure and Magnatec certainly hasn't improved this. Running hot at 3200 rpm 30psi.

Recently someone put a link to the Dutch SD1 website and I have found this particularly useful for motor and carburettor (SUs) information. This site quotes the correct oil pressure at 27 to 32psi which makes me more comfortable with mine.

Ian G Buckley

I have recently discovered that you can get oil filters with an anti flowback valve in them, they are now quite common (they may well have been before but I didn't notice). I tried one of these and at this early stage it seems to have worked, lots of noise on the initial start up (heart stopping), but since then music to my ears. Note however I've only had this thing going about two weeks (using Magnatec) but so far so good.

Whilst Magnatec for older engines didn't stop any start-up rattles it has improved the hot idle pressure and consumption over the 15W/40 GTX that has replaced the 15W/50 that I used for years. 10/W40 sounds like the variant for modern engines, the packs are very similar excepot for that little bit of wording. I found Duckams did nothing for the oil pressure and went opaque on the dip-stick after 100 miles whereas Castrol just gets a slight brown tinge over 3k. The factory V8 manual quotes a hot idle of 34 and a running of 42. My engine with about 180k on it runs at 38 and hot idles in the low 20s, although if stuck in traffic it drops further until the fans cut in. AFAIK Unipart filters, and others, have had the anti-drain-back valve in them for years, it is only the cheaper brands that don't.
Paul Hunt

Do you need an anti-drainback valve if using a right-side-up oil filter? ... does it drain out when the car's stopped? ... I ask because when I go to change the filter, it's full of oil.


What brand oil filter are you using? I have Ryco.

10w 40 is the only Magnatec sold in Oz.


Ian G Buckley

Ryco for no other reason than it was the first my inexperience eye fell apoun.

Ted, This is true however I hope that the valve may help prevent the exterior oil lines draining, the principle cause (I think) of that start up "deathrattle". I sited my oil filter a little lower than usual with this in mind. It's early days yet but we shall see. If the "deathrattle" fails to appear in the next month or so I'll post a thread, otherwise I'll maintain a discrete and embarrassed silence

I think Peter is right mounting the filter lower may well help. If I disconnect the oil pipe from the filter housing to the oil pump, the one closest to the driver. There is no oil spill and obviously some oil drains down this pipe and through the pump. You can't see oil down it. I also wonder if some oil from the other side of the filter syphons back through the pump via the oil cooler??

Peter, which Ryco are you using mine is a Z418.

Ian G Buckley

Thanks lads, I have also a vauxhall astra(wifes car)Has done over 150,000 miles. It was my first company car and i bought it when its time was up. It was always oil changed with semi synthetic. The oil was almost as clean when i used to take it out every 6,000. I then used Castrol GTX (what i use on other MG)The oil was filthy next change, hence me asking if semi sythetic can keep the muck down.

The astra is as sweet as a nut after all these cant be that bad And I bought the oil it direct from vauxhall dealer......was cheaper than GTX!!

Z 15 somthing I'll have to go look (I'm currently at work). Infact it is not an axact fit (the filter, not work, although an arguement could be made)being about 2mm too narrow, but it doesn't leak at all so I might stick with it. At the moment I'm waiting for 'Brown Davies' to finish putting a swirl pot in my tank (and waiting and waiting, wish I'd hired a TIG and done it myself), it's the last obstical. Any way when I get it back it will have been more than two weeks since I had the car running so we'll see if the antflowback valve and siteing the filter a few inches lower works.

Just a small point, but isn't the idea of using a high detergent oil was that it keeps the muck in suspension, thus getting dirty! If it stays clean surely this means that the dirt is deposited elsewhere in the engine. I expect to see it get dirty. Apart from anything else it makes it easier to read the level on the dipstick.
ian thomson

Absolutely - the dirtier the more effective the cleaning - Ian.

Picking up on the anti-flow back valves- a precautionary tale - I understand that in the 80s a significant number of Peugeot drivers ruined their engines by using filters with inappropriate pressure release valves.

I realize the object here is to reduce rattle on startup but if pressure is a concern, moss (used to) sell a stronger pressure release spring for the standard pump.... increases pressure by 2-5 lbs.

IMHO (in addition to 3K oil changes) it is better with high volume (rather than high pressure) lubrication systems to have as much oil in the sump as permissable to slow down the degrading process. This also helps the anti-rattle.

With the OE 3.5, I used the cheapest 20-50 since with a few notable exceptions, the characteristics of lubricants on the high street are pretty similar until the 3K mark. Why pay 20 when 6 will do. But it's a different story with the 3.9.


The pressure relief spring was changed early on in production, as new owners were more accustomed to 1800B oil pressure. I won't quote the figs as my memory is getting terrible, but it resulted in 2-5psi over what had gone before. This is a worthwhile mod on early cars which have not been done, and can be achieved with various sockets and UJ's while lying uncomfortably under the car.
The second oil pressure issue was the significant delay in registering at the gauge on early cars, causing complaints at the dealers. The take off was moved from the remote filter housing to the oil pump to improve matters, without too much success.
I always turn the engine over first - for a few seconds - with the choke in, to prime the oil pressure.
If you do that, it won't rattle when it fires.
Prior to rebuilding, I suffered a distinct bottom end rattle on start up. The big ends were OK, but the mains were absolutely awful, with incredible grooving.
Funny thing was, with all new parts, there was no difference to the oil pressure.
Dave Wellings


Ryco Z158

I started up the car (after about three weeks) and guess what? no "death-rattle". It looks like either the oil filter with the antiflowback valve, or siteing the oil filter a couple of inches lower (about level with the alternator bracket) stops this happening.


I just saw your last post, I have been overseas for 10 days. It is good to hear that you have no death rattle. Will start mine tomorrow with a keen ear!!

Ian G Buckley

This thread was discussed between 21/01/2003 and 13/02/2003

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