MGB & GT Forum

Hello all,

Bit of a mystery. My 1978 'B' is so predictable that I know something is out of whack here. The engine is a little tired and so when warm, I get 25lbs at idle and 50-55lbs at 50mph or so. Been like this for years. However, the last few rides I've noticed a new noise. On coming off the revs, I can hear an engine noise that sounds like a dry leaf in a heater vent. Its a low ticking noise - sounds a bit 'tappety', but usually only on de-accelration. So today I had to run an errand and sure enough there's the noise again but this time my oil pressure is at 50lbs at idle and climbs to 60-70lbs at driving speeds. Never seen that idle pressure in 10 yrs of owning the car.

Now unless the MGB fairies overhauled my engine in the middle of the night, something is wrong. Can anyone suggest things to look for?

Thanks all.

Sticking oil pressure relief valve ?

John Twist on oil flow:

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“What seems to be, Is,
To those to whom it seems to be...."
William Blake



Edited 1 time(s). Last edit at 2015-03-02 06:36 AM by MG Dog.

I am going to guess that rod bearing shells have rotated (spun) in the big end of a rod (#2 or #3?) and have blocked off the oil feed hole from the crankshaft causing the oil pressure to rise. I hope that I am wrong.

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Be safe out there.
Kenny

Any other guesses that aren't so depressing?

Car is running great apart from the intermittent strange noise and the new +25lbs pressure. I'm not sure if I should keep driving it though.

Thanks all.

Kenny's theory is brilliant, athough depressing.

I'd stop driving it and drop the oil pan to inspect the rod bearings.

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Friends talking around a fire is the history of mankind.

The question that comes to mind is a worn thrust washer set. Are you running a heavy duty clutch in place of the standard clutch/pressure plate assy.? I don't have a good experience/knowledge base to determine what symptoms a worn thrust washer set would create so further investigation would be needed there.

If you have changed your oil filter recently then check out this thread:

Purolator PL20195 & Other OIl Filter Issues

Oil pressure relief valve: check
Faulty obstruction w/ and oil filter: check by replacement
Faulty oil gauge: check (not a cause for the noise though)
Worn Thrust Washer Set: .......ummmm

The crank thrust washers have nothing to do with oil pressure and the oil pressure relief valve would not really make the sort of noise you describe but check it as a first step simply because it's the quickest and easiest thing to do.

If that pans out OK then you have 2 choices:

1. Pull the sump and check your bearings.

2. Carry on driving until something goes bang !

The advice to "Carry on till something goes bang!" is not adding much to the conversation and in fairness to John H. of WA, I'm sure the rest of us would like to know whatever you find out with this MG anomaly and when we have more information, maybe we all could learn something.

That was not advice but a summary of the limited options, doh !

Hi drive it like you stole it. I would think its something simple like the oil gauge or sticking pressure relief valve if it goes bang well then you got to fix it mike

If you feel better with checking something extra: why not drain the engine oil an extra time and let it pass a sieve. If you've got metal parts lying on it, you at least have a serious reason for further investigation. If nothing is found you are not any wiserm, but who cares? This is not my advice, but just a possibility for action

What was it I heard years ago??? "Nothing's more scary than owning a car that "fixes" itself"??lol!

In all seriousness...I'd take the advice of others and drain the oil and drop the pan for a little investigation. As potentially "depressing" as what you may find may be...it's better to know your enemy.

The tinny "leaf" like description however leads me toward the filter. The filter's relief valve is thin spring metal in many cases. If it's gone flaky...that COULD be a possibility as well and a much easier fix.

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

Thanks all. My first step is to add ATF fluid to the engine (to flush it), drain, and then replace oil and filter. I will get the 'easy' things checked off the list before ramping up to tackle to removal of the oil pan. Removal of the oil pan is non-trivial and I learnt a long time ago to adopt the 'baby steps' principle.

A Story:
Years ago, I was deemed the local 'computer guy' in our neighborhood. A retired neighbor was having issues with no sound coming from his new PC. So I breeze over there and over 2 days: removed and replaced his audio card, removed and re-installed his sound driver, and finally re-installed his whole operating system on his PC. At the end of day two of my genius, his wife walked into the room, where we were still not getting any sound, closed the curtains and asked "Is this plug behind the curtains supposed to be out of the wall?". Yep, the speakers were powered and had been unplugged days earlier. Plugged in the speakers and everything was fine again.

So since that day, I have approached the 'baby steps' approach. Not to say it isn't a bigger issue than my hope of sludgy oil but I will chance $20 to find out

I will add the ATF fluid tonight and let you guys know. THANK YOU for all your input.

UPDATE:

I don't want to jinx it but from advice on another thread I added ATF fluid to my roadster tonight (as an oil cleaner) and ran it for 20 mins. After 20 mins at 2000rpm, NO SOUND and the oil pressure dropped back down to 25 lbs at idle. I'm very happy but I still need to road test the car. When warm, and seeing I was at home at wouldn't have to 'walk', I really pushed the motor into the 3500 rpm range. No clicking and no rumble from the engine. I took my foot off and the pressure fell back down to its normal 25 lbs at idle.

I really hope it was a sludge blockage and the ATF fluid freed it. I know its early days and I still need to road test, but I'm hopeful.

In any case, thank you all!!! The process of swapped ideas and thinking is what gives us all the best chance to keep rolling.

first step, notwithstanding the above 6-sigma extremely unlikely scenarios, would be to verify that the gauge is accurate

then do step 2