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MG MGB Technical - Oil Change and no pressure on gauge

Dear All

I've followed some of the threads on a similar topic to this but none seem to fit my current problem.

All I needed to do was change the oil and filter on my 1980 BGT. On refilling and restarting the oil presure gauge refuses to budge. (and as an aside there is a distinct knocking that wasn't there before, I think, difficult to tell with these engines) Prior to refilling it registered the book values for tickover and running.

Please help, it's getting late, dark and I can't sleep.

Darren
D Paine

It does sound like youve got no oil pressure, in which case dont run the engine. It could be that your oil pump needs priming. Ive never heard of this on a B but I had this on a mini once and I cured it by draining the oil out and pouring it in quickly again. Even if your relief valve was stuck( and Ive had that before) you would register some pressure. How long did you leave it run it can take 20 seconds or so to fill the filter. You may have air in the pipe to the gauge but again that would make the reading eratic rather than zero. I'd hang on if I was you and some sage from this BBS I'm sure will tell you the answer. But don't worry oil pressure can't be there before oil change and there be none after, there has to be an explanation
Paul Hollingworth

Darren-
The knocking that you heard was almost certainly the connecting rod big end bearings. That's a sure sign of no oil pressure. Reprime the lower end of the engine by pouring oil down the center tube of the oil filter stand, then prime the oil pump by pouring oil down the side hole of the loi filter stand. Screw donw the oil filter tight and start the engine. If you don't get pil pressure within twenty seconds (that's the maximum time for the oil filter to fill with oil), then shut it off and check to see if the oil pressure relief valve is stuck.
Steve S.

Darren. What you describe, if all is working correctly, cannot happen. As the others have noted, you will get full oil pressure in 20 seconds, or less, after a normal oil change. Since this did not happen, you have some form of very uncommon problem. Most of us have never seen such a thing and, most probably, never will. Hence, we can only speculate.

You should have a direct reading gauge (the gauge operates directly off the rear fitting on the block and you do not have a oil line to the electric sending unit, then a wire to the gauge as some models did). The direct reading guage seldom causes problems and, normally, give a fairly accurate reading (within + or - 5 psi say). You could hook a second gauge to the engine to see if the dash guage is actually working. But, with your mention of what seems to be rod knock, I suspect that your gauge is reading accurately.

To check for oil flow, remove the spark plugs and remove the line going to the rear of the block. This is the line going to either the oil cooler or the oil filter adapter. (Note: if you have a metal line, as did the NA spec cars in 79-80 when not fitted with an oil cooler, disconnect at the oil filter adapter. Three of the four I have removed have twisted at the rear fitting when loosening.) Recruit an assistant to turn the engine over on the starter for 30 seconds. You should see oil flowing out of this point if there is oil pressure. (I use a cut down plastic bottle to catch any oil). If there is no oil flow, it is a bad pump, cam timing chain or oil relief valve. If there is flow, the oil should be getting to the filter.

Remove the oil pressure flex line at the rear of the block and have your assistant crank the engine over again. If you see oil flow, you have a bad gauge. If you do not, you have a problem with the oil filter you fitted and it is not allowing the oil to flow through the system.

About the rod knock. This is very bad. It probably indicates significant engine damage as Steve S. alludes to. I have little experience with this. My daughter had a freshly rebuilt engine loose an oil line. The engine was shut down when it began to knock and the oil pressure dropped to zero. Replacing the line with a new one and starting the engine produced a brief knock, then a quiet running engine. When I tore the engine down, there were bearing chips throughout the pan, the rod bearings were scored, the main bearings were scored and the crankshaft journals (all) were scored. With my daughter's engine, a complete lower rebuild was required. I have some similar experience with rod knock on my Bronco and a friend's Scout. We ignored the problem and got by with it for several months. However, both engines threw a rod and neither engine was capable of being rebuilt. At the very least, I would suggest that, after the problem is diagnosed, you drop the pan and pull the con rod lower ends to inspect the condition of the bearings and journals. Les
Les Bengtson

Thanks for the help everyone. I spent most of last night reading through the archive which made for a very restless night.

First thing this morning I swapped the oil filter back to the old one (it was only six months old anyway) and fired her up, oil pressure at normal (60psi) in a few seconds. The new filter was a Unipart type which others seem to have had problems with in the past.

Hopefully all is now well!!

Great forum by the way. I've only had the car six months and wish I'd found this earlier

Darren
D Paine

May I suggest that you have a serious conversation with your filter supplier.If the filter is bad then they should be liable for your problems.
Sandy Sanders
conrad sanders

Darren, In addition to the suggestion by Sandy, you should have your supplier return the filter to the manufacturer for an analysis of what went wrong. If there is a batch of the same type filter in the supply system it's important to get them out before several engine are ruined. You may want to look at this site to see how an oil filter is constructed. All oil filters I have seen have two safety valves to prevent what you experienced, so in your case there has to be a serious defect. Hope you engine isn't damaged. Clifton
http://www.ntpog.org/reviews/filters/filters.shtml
Clifton Gordon

I had a similar problem with my '79 B. The filter was very tight on the spigot which sticks up in the centre of the oil filter mount and had only a few pounds pressure on a new motor. Different filter and no problem. The message here is if your filter is tight on your spigot (someone can make something of that one!), throw it away.
Greg

That's the first problem like that I have heard of with a Unipart filter, or of any other type for that matter. There have been observations that currently available Uniparts and Champions drain back which delays oil pressure rising for a few seconds after not running for even a relatively short time. I have just purchased a Fram filter, which are supposed to have an improved anti-drain back valve, to see if it is any better than the ones I am used to.
Paul Hunt

D Paine seems to have missed the observations that there may be serious but not yet fatal engine damage as a result of this misadventure. It is his money, and his beastie which will suffer, but If it were me I would at least dissect the current filter and inspect for metal, pull the pan, and maybe a rod cap or two. The defective filter should be kept as evidence. With some trouble, engine damage may be covered as a liability matter. Court is best avoided, but serious talk and threats to suppliers can get the damage covered.

I used Fram for years, but recently discovered that many enthusiast clubs have found that they are nowadays of extremely poor construction. A local parts store has one sectioned and it is garbage. There are many reports that 10-15% of AC-Delco filters fail on startup. These things are frequently made under contracts which shift fronm time to time, so that names mean little and today's good one is tomorrow's new engine! Don't know how to solve this one. Certainly visible problems like poor fitting or malformations are best avoided.

Drain back as mentioned is either a wrong or defective filter.

Here is a good link to modern filter and lubrication.
http://www.shoclub.com/lubrication-oil/lubrication-oilpart1.htm
Somewhere on the SHOClub site is a link to one of the Fram studies, but google search should turn up others.

There are two types of filter mounts for the B with the upside down filter. One has a short spigot which lets it drain back if the filter antidrain valve fails. The other has a long spigot which prevents drainback itself.
As anyone knows, a long spigot is better!

FRM
http://usachoice.net/gofanu
FR Millmore

Funnily enough when I bought the Fram I compared it to a Unipart to make sure I had been given the right part number and explained why to the chap behind the counter. When I mentioned the supposedly better anti-drainback valve he raised one eyebrow but said nothing. The only reason I am trying one is because the MGOC have only recently started selling these using the valve as its USP.

Another oil filter study: http://www.frankhunt.com/FRANK/corvette/articles/oilfilterstudy/oilfilterstudy.html

Hmmm, maybe I've bought the wrong thing.
Paul Hunt

Never tried a Fram in an MG but have had lots of filter anti-drain valve leak down problems with them in OHC engines. I have used Motorcraft, Wix, Purolator and Unipart in MG's and never had a problem with any of them. FWIW, Clifton
Clifton Gordon

I recently over zealously drained the oil and replaced the oil filter on my O series engined Montego Turbo. The O series is basically a B series with an overhead camshaft and both engines have much in common.

I too had zero pressure thereafter. I believe 'over zealous' by running the engine for a few seconds to drain out the last of that old oil after fully draining the sump (USA = oil pan)- DOH! - I'm guessing here that was the cause but, can't be certain - thus in so doing removed the oil from the oil pump so it would need to be primed - still guess work though.

Posed several questions on various BBS sites but after lots of personal 'brainstorming', I primed my oil pump with fresh oil using a plastic 3 litre (approx six pints) Supermarket milk container.

For a comprehensive description, here's the thread I started:

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=7&subjectar=7&thread=200312122211557934

Maybe it'll do the trick next time someone has this oil pump priming problem. It certainly worked for me...;-)

John
John McFeely

There is no need to drain the last drop of oil. The acidity and debris load of those few drops will not have any measurable impact when swamped by the new .
S Best

This thread was discussed between 01/05/2004 and 08/05/2004

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