31 replies to this topic

[miniGTS]

The engine I have in my car now is one I rebuilt many years ago but hardly used. Bores are very good, head is good but I suspect bearings may not be so good. I discovered, after connecting up an oil pressure gauge, that my oil pressure is really low at 1000rpm once it's all warmed up. It's at about 100kpa and goes up to around 300kpa when I take the revs up to about 2000rpm and doesn't really go higher than that. When the pressure is low and I give it a rev, I also can hear a whining noise coming from the engine bay. The noise is heard when I lift my foot off the accelerator and the revs drop.

At cold start up it sits at 500kpa at 1000rpm and then slowly drops as it warms up.

My plan is to get as much as possible out of this engine before I have the GTS engine and gearbox rebuilt by someone better skilled than me.

In the meantime, is there something I can do to get the oil pressure higher as a temporary option?

[nicklouse]

Ok 100kpa is about 14lbs

300 is about 45lbs

500 is about 70lbs

 

first thing I would do is remove the pressure release valve and check condition and clean it and everything else in the area.

 

it could be sticking.

 

standard valve “blows” at 70lbs

 

if after cleaning and checking it is moving freely you have the same issue then I would say engine out time.

[miniGTS]

I had it out and cleaned it up a bit and also inside. It had score marks on the side of the little piston , 1 noticeably pit mark on the angled head and also what looks like a flat spot on the side. I'm ordering the ball type valve and new spring and will see after that.

If it is a case of engine out, I'll probably do this one's repair myself and try to do a better job than before.

Let's hope though that a new relief valve helps with the problem

[miniGTS]

When you say the standard valve blows at 70lbs, what do you mean?

I noticed that mine doesn't go over the 500kpa when cold, even if I rev it up the 2000rpm. When cold it also doesn't make that whining noise I mentioned.

[timmy850]

What he means is the standard pressure relief valve opens when the pressure gets to 70psi (500kpa) and the pressure doesn’t get any higher than that

[Spider]

Working off the Metric -> Imperial conversion that Nick has done, there's nothing in the world wrong with it.

[miniGTS]

So the problem is elsewhere. Oil pump or bearings then... So it's likely engine out to properly fix the cause...

Or will an oil additive and/or increasing relief valve spring tension buy me some time with this engine. I'd likely increase spring tension first and test before adding an oil additive if it'll help treat the symptoms for now.

Edited by miniGTS, 17 January 2025 - 05:39 AM.

[Lplus]

What he means is the standard pressure relief valve opens when the pressure gets to 70psi (500kpa) and the pressure doesn’t get any higher than that

Mine opens at 60 psi hot at about  2750rpm and never goes above about 65 -70 even at peak revs.  Cold it still blows at 60 psi but goes to 75 or more cold with revs.  I tried a cooper S ball and spring but that didn't blow off till about 75 hot and made 90 + cold. Oddly after blowing off hot the Cooper S ball alloed he pressure to drop to 70 psi before rising again with revs.

 

I understood that the pressure specification requires 60 psi at 3000rpm hot.

Edited by Lplus, 17 January 2025 - 07:21 AM.

[timmy850]

 

What he means is the standard pressure relief valve opens when the pressure gets to 70psi (500kpa) and the pressure doesn’t get any higher than that

Mine opens at 60 psi hot at about  2750rpm and never goes above about 65 -70 even at peak revs.  Cold it still blows at 60 psi but goes to 75 or more cold with revs.  I tried a cooper S ball and spring but that didn't blow off till about 75 hot and made 90 + cold. Oddly after blowing off hot the Cooper S ball alloed he pressure to drop to 70 psi before rising again with revs.

 

I understood that the pressure specification requires 60 psi at 3000rpm hot.

 

The AKD4935 manual says the following for 850cc engines:

Relief valve opens 60psi

"Normal running" 60psi

"Idling (minimum)" 15psi

 

The Cooper & S engines:

Relief valve opens 70psi

"Normal running" 70psi

"Idling (minimum)" 15psi

"Oil pressure (normal running) 60psi at 70C oil temp

 

There are many different springs available now, plus they get old and relax, plus the tolerances between the plunger and bore wear out over time. 

[gazza82]

... I'm ordering the ball type valve and new spring and will see after that. ...

Might be a backward move ... they can 'flutter' ...

[miniGTS]

 

... I'm ordering the ball type valve and new spring and will see after that. ...

Might be a backward move ... they can 'flutter' ...

 

 

Thanks for that feedback. So I'll try what I saw on a MG forum where they added some thick washers inside the cap to add tension to the spring.

 

It seems my pressure isn't too far off the minimum spec so if I can do something small to get the pressure up, that should keep it going for a while longer before the cause gets worse... I assume...

[nicklouse]

 

 

... I'm ordering the ball type valve and new spring and will see after that. ...

Might be a backward move ... they can 'flutter' ...

 

 

Thanks for that feedback. So I'll try what I saw on a MG forum where they added some thick washers inside the cap to add tension to the spring.

 

It seems my pressure isn't too far off the minimum spec so if I can do something small to get the pressure up, that should keep it going for a while longer before the cause gets worse... I assume...

 

Have read https://www.theminif...huttle-vs-ball/

[Cooperman]

What oil are you running and what is the pressure like when fully warm and it's revved to 5000 rpm?

[miniGTS]

What oil are you running and what is the pressure like when fully warm and it's revved to 5000 rpm?

 

I'm in Cape Town, South Africa and it's summer here so upper 20 degrees. The oil is Ravenol 20W50 and I've never revved it that high. Highest while driving has been 4000 rpm but will see

[nicklouse]

Another thing to remember. The valve is only there to stop over pressure.

 

ps do your engine a favour and get the revs up to 5-5.5k. They will go way more on standard parts.