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MG MGB Technical - Castrol GTX 15W/40 Oil

Hello all,

I would like to find out if GTX 15W/40 is good enough as a subsitute for 20W/50 because I can't find it anywhere here in Hong Kong. Also, anyone out there using the more expensive GTX Magnatec 15W/40 Oil? Thanks!
Aaron Liu

Aaron,

I've started using GTX 15w/40 in my car, but see my thread "No oil pressure on startup". Paul Hunt uses it with no problems, but it appears too thin in my car and is draining out of the inverted oil filter when the car is left standing for several hours. Result is that when started there is zero oil pressure until the filter fills back up again (5-6 seconds). Not good!

Tim.
Tim Jenner

I've used 15W/40 in my car, but later swapped to 20W/50 when the engine passed 80,000 miles.

Tim - you need to investigate about finding an oil filter with a better anti-drainback valve.

Here in the states, WIX manufactures a sturdy line of filters under several different brand names.

Sometimes, I use a Motorcraft FL-1A (Ford V8) on my B/GT without problems. It installs fine and is
almost twice as tall as the stock MGB filter (it needs almost an additional quart of oil to initially fill it).
The advantages are: 1) Cost. About $4. 2) Availability. Almost any US auto parts dealer carries them. 3) They have much more filtering surface area of a stock MGB filter. 4) It uses sturdy
components, including: the can, base, filter construction, anti-drainback valve.

Some of our local Chrysler-MOPAR fans have done a filter comparison, including autopsies and anatomical exams of several different brands of filters which you might find interesting.

I do not know whether if any of the filters in the study are available in the UK, but at least it'll show
you some points to look for.

http://minimopar.net/oilfilterstudy.html
Daniel Wong

Doesn't seem to make any difference in the roadster but I'm sure I noticed lower hot idle pressures in the V8 - which is reknowned for low pressure anyway - before I noticed the grade had changed from the GTX 15W/50 I used to be able to get. I tried GTX Magnatec 15W/40 in the V8 and it did seem to be slightly better but not much. But it is very expensive, doubly so as there is only 4.5L in the can instead of 5. I'm currently trying Halfords 15W/50 in both the roadster and the V8, again no difference in the roadster, too early to say with the V8, but it's possible that the initially slightly higher hot idle pressure is dropping off as the oil ages, and that over just a few hundred miles. Whichever type of GTX you get look carefully at the container, as here in the UK there are versions for both 'modern' and 'conventional' engines in both standard GTX and Magnatec and the containers are very similar. Always use 'conventional'. The Workshop Manual quotes various grades from 10W/40 to 20W/50 as being suitable for 'temperate' climes, with 10W/40 or 10W/50 for colder, and 5W/20 or 5W/30 for very cold.
Paul Hunt

Hello,

Well, as mentioned in my original posting the GTX 20W/50 is no longer available here in Hong Kong. I changed my oil with Castrol GTX 15W/40 this afternoon. After the engine is warmed the oil pressure at idling is right at the middle of the gauge so I guess it's fine for now. But I did not drive it very much after the oil change so I think I'll wait for a few miles to see if it really makes a difference. Paul, I did not notice the "modern" or "conventional" part on the green container. I'll pay another visit to the store to have a look at it.

Aaron :-)
A LIU

Aaron - in the UK the Magnatec container is predominantly green, 'standard' GTX is predominantly white, see http://www.honest-johns.co.uk/acatalog/HONEST_JOHNS_CASTROL_123.html
Paul Hunt

Oil needs a few hours running to settle in. The actual multi-grade additive will shear in service and settle so check your running and idling pressures when the car is warm after the first 50 miles or so after the service.

In fact, the worse case for multi-grade oil is the Mini and 1100 with the gearbox in the sump. The shearing action of the gears is quite lethal for the multi-grade additive and can turn a 20W50 oil into a 10W30 oil in short order.

Martin

Hi Paul,

The container that my regular GTX came in is definitely packaged differently than what's shown in the web-link. I'm sure I didn't get the wrong one because it's the cheapest on the shelf :-) The Magnatec is at least twice as much. I didn't even check for where it's made, oops! I suppose it's made somewhere in Asia.

A :-)
71 B roadster
Aaron Liu

This thread was discussed on 25/04/2003

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