Oil pressure slow to register
QUESTION:-
I would like to ask your advice about an oil pressure problem on my YT (Y/T/EXR/3663). When I start the engine whether hot or cold the oil pressure on the gauge climbs up very slowly eventually reaching just over 40 psi and when I switch off the pressure diminishes just as slowly!
When I bought the car eighteen months ago I fitted flexy oil pipes from pump to filter and from filter to engine and also a spin on filter conversion. I temporally tried another oil pressure gauge and pipe but with the same result. Could it be a clogged oil strainer in the sump? ( I hope not) I have driven several hundred miles with this problem with no noticeable detriment. Your advice would be appreciated.
Following your comments in a recent Bulletin about taking the gauge feed from the bottom banjo union rather than the cylinder head end, I checked my TD and the gauge feed was taken from the top which probably accounted for the rather poor oil pressure ( 50psi cold diminishing to 10psi at hot tick over). This is how it was done in the factory! However, I changed the banjo union bolts top to bottom and extended the gauge pipe, started the engine and instead of the usual 40-50 psi I had 130psi which of course is far too much. On investigation I found a very stiff supplementary spring in the oil pump relief valve. When I removed the spring and just left the standard one, all was well.
ANSWER:-
There were sets of flexible pipes being sold that had a fae too small bore. This tiny bore was a serious restriction to the oil flow. The gauge is just that, a non too reliable indication of pressure. Thick cold oil will take time to gets its reading to the gauge, but should come up almost imeadiately when the engine is hot upon re-starting. The narrow oil feed pipe to the head (rocker shaft) is a deliberate restrictor in the system to reduce oil flow to the top of the engine; the rockers only need about 20psi.) When you start the engine the oil pressure has to ‘unwind’ a curled tube in the gauge that is connected to the needle, this can take a few seconds (that seems like minutes).
The only real way to see what the running pressure is, hot, is to put a gauge direct onto the oil gauge pipe connection at the base of the rocker feed pipe. Engine hot a 30mph should read at least 40psi ( about 2,300 rpm). You may well have a worn oil pump and if the oil has not been changed regularly every 3,000 miles, the strainer in the sump may have a lot of gunge on its mesh. You could use flushing oil and the oil filter will catch all the muck, follow the instructions. Oil pumps usually wear at the ends faces of the gears and into the end plate. This can be cured by lapping in the end plate until there is just 0.002″ end-play. (You need to remove the pump to do this and its a pig to get off in-situ).
My engine after 45,000 miles from its rebuild gives 75psi cold; 45psi hot at 45mph; 10psi at idle hot after a good long run. I use SAE 20/50 with a tin of Wynns or STP every 3,000 miles.
The other fault may be a worn pressure relief ball bearing. Its under the big brass nut under the oil pump. They often have ring grooves in them worn over the years. Fitting a new ball bearing, tapping it firmly to seat it, often cures it from leaking back into the sump. Also a new relief spring might be in order as they wear on their coils at the sides. It is not unknown for some to put a washer under it to increase the pressure and oil flow (often done in the 1950s to hide a worn crankshaft…..).
My guess is those flexible pipes have a too small bore restricting oil flow.
Oil pressure
QUESTION:-
Starting my TC with TD engine my oil pressure gauge takes 5 seconds to reach 20 p.s.i. then takes a further 40 seconds to reach 42 p.s.i. with higher rev s and maintains this whilst driving.On turning the engine off the gauge drops to 20 p.s.i then stops for a few seconds before dropping to zero. I have had the gauge checked no problem .All the pipes have been cleaned out.Is there a reason, and can I cure it thanks Dave C
ANSWER:-
Quite normal. The gauge itself reads what arrives in the tiny pipe and the ‘Bourdon Tube’ (the pressure tries to straighten it out, this movement works the needle) inside takes time to expand to then move the needle via a tiny rack-and-pinion. If its all cold it takes even longer. Whilst the pressure in the engine will be almost instant in the main oil gallery, it has to pass up a long, thin copper tube, thence through a rubber flexible tube, then into the gauge itself. The gauge is a cheap typical type of its age and is only an ‘INDICATION’. On stopping, you will get residual pressure still in the pipe as it releases itself back into the engine (Note there is no ‘FLOW’ only a pressure,). You are probably expecting too much from a simple, basically 1930s, mechanical system; a modern system from a digital pressure switch on the engine to an electrical gauge would read instantly. If you re-start from a warm engine it will probably read more quickly, its not the engine that is ‘SLOW’ but its indication system.
QUESTION;-
Oil pressure readings
I am member No. 5951 and i have a problem with my MG TD which i thought you may be able to advise me on. My TD is 1951 and the problem is that the oil gauge needle has started to flicker when the engine is either on tick over or not on load when motoring. I have changed the spring and chrome ball in the pressure relief valve and i have just changed the oil pressure gauge, but neither of these has cured the problem. It may be the oil pump itself, but removing it from the car is not easy, and i am not sure if the bits are available to carry out the repair. I would appreciate your advice.
Many thanks.
ANSWER;-
Not enough info….what is the oil pressure cold, and what is it with a hot engine at 40mph? A fluctuating gauge at low rpm is just it reading the pump’s pulses. The pump is capable of moving 30 gallons a minute at max rpm, the only thing one can do with it is lap-in the end plate to removed too much end play. If the pressure at 30mph is over 40 psi at normal temperature, there is not much wrong with it.
QUESTION;-
Oil pressure problems
On 13/07/2016 14:12, MG Octagon Car Club wrote:
I have had this email from a member regarding the oil pressure on his XPAG engine in his TC. I have sent him a copy of your article on the XPAG oil system from the International Y Register site. Have you any Ideas?
I still have oil pressure problems! I have : Changed the oil & filter. New copper pipe to gauge Fitted a new service exchange gauge from Chris Clark. I have discussed the problem with other engineers and they say– It
defies logic! From Cold Start at tickover – No oil pressure @ 1200 revs – 10 PSI As engine warms to 40 degrees – 25 PSI @ 2000 revs “50 – 60 ” – 45 PSI this is normal running pressure
When the engine is cold it drops to nil at tick over. At running temp of 70 Degrees it drops to 10 – 15 PSI at tickover. The information you sent to me does not relate to any of these problems.
ANSWER;-
1) Put a test gauge onto the pipe on the engine, that new gauge might be faulty.
2) Seems the oil is almost acting as an RPM gauge, ie higher pressure at higher rpm. The oil pump’s relief valve may well be leaking internally, often a new ball-bearing will cure this as the old one develops grooves from its seating.
3) Is the correct filter element fitted (if a separate item)? It may be only letting oil through a little until the pump builds up pressure and lifts it off its seating (it acts as its own relief valve) so full pressure then gets through?
4) If using modern 20/50, its too thin. Either add some Wynns or use relevant Summer oil in the handbook (SAE30?) OR the oil is far too thick and only thins when warm, the pump struggling to move it when cold (and dumping it via the relief valve) but when it thins a little when warm it pumps easier?
5) May well be a mixture of these suggestions.