again oil pressure

[rudi]

My recently rebuild engine shows 100 psi pressure when cold  at idle. When warm/hot the pressure drops to normal levels (70 at 2000 and 30 to 35 at idle). As I am afraid that this high pressure might blow seals I would like to adjust the oprv. Does anybody have any experience? Should I do this with a cold engine at idle and turn until the pressure goes down?

Apart from that I am asking myself WHY the pressure at cold is that high? Can the oprv be faulty or is there another reason?

[Sam]

Not sure that the adjustment can be made with the engine running. It would probably be much safer to do it switched off by trial and error.

 

The pressures seem quite high the prv is only designed to operate when the oil is cold. I assume that the 70 psi value is when hot. My recently rebuit engine registers around that when cold dropping to 55ish when hot. Mabye your gauge is reading high?

 

Sam

[Don Elliott]

Adjust the pressure relief valve setting on the alum body of the filter assembly down to 70 psi and test it with the engine cold.  This will allow more oil flow at a lower pressure.  I prefer more oil flow for the bearings which will lube them better.  Having a higher prv setting causes the oil to get hotter than with a lower setting.  Cooler oil at a higher flow rate is my preference.

 

Don Elliott, Original Owner, 1958 TR3A, Montreal, Canada

http://mysite.wanadoo-members.co.uk/trebor/don3a_big.JPG

[marvmul]

When the prv is adjusted to 70 psi, more oil is directed to the sump again, instaid of entering the oil gallery. So lower psi means less flow to the bearings.

The engines are 40 - 50 years old, so al lot of prv's are adjusted at some time to get an higher oil pressure. The pressure is set at 70-80 psi in the factory. Higher pressure opens the prv, thus directing oil to the sump.

Adjusting the prv should be done when the oil is cold, do it in steps till you get a pressure of about 80 psi when starting up.  I think 100 psi won't do any harm though, so you could leave it alone , or adjust it to about 90 psi, because the gauge reading may be false high.

[marvmul]

Adjust the pressure relief valve setting on the alum body of the filter assembly down to 70 psi and test it with the engine cold.  This will allow more oil flow at a lower pressure.  I prefer more oil flow for the bearings which will lube them better.  Having a higher prv setting causes the oil to get hotter than with a lower setting.  Cooler oil at a higher flow rate is my preference.

 

Don Elliott, Original Owner, 1958 TR3A, Montreal, Canada

Don - I think there is a misunderstanding about the prv : if the prv would be functioning simply as a restricting valve, you would be right, but it is a by-pass valve, just like the prv in the PI system : lowering the prv pressure means more fuel returning to the fuel tank.

[Don Elliott]

Thank you Gents - I stand corrected.  The higher pressure setting will heat up the oil to a hotter temperature and the oil returning to the sump will become hotter, for no good reason.  This will thin out the viscosity of the oil so the oil being pumped to the beaings will be less viscous.  Not as good as if the oil was cooler and thicker.

 

With my TR3A, I have had the cold prv setting at 70psi and hot at 3000 rpm in overdrive gives me 55 psi when the ambient air temperature is 30 deg. C.

 

I have driven this engine more than 82,000 miles.  I changed the con-rod shells after 30,000 miles and the mains and con-rods again at 52,000 miles. Guess it's time to do them again.

 

During the last 3 weeks, I drove 3383 miles arriving back home on Sunday.  I drove 794 miles that day for an average speed of 67.6 mph after I subtracted the stop time for petrol, eating and other essential things.

 

What I'm saying is that an engine that gives 70 psi with cold oil does not need to be at 100 psi to be an endurable engine.

 

Don Elliott, Original Owner, 1958 TR3A, Montreal, Canada

[Roger Glover]

rudi,

 

I don't know if this will set your mind at rest, but my TR4A when started from cold will produce a <true> 100+ psi oil pressure at any thing above idle. However at normal working temperatures it max-es at 50 psi - that's from 1500 to 5000 plus rpm.

It appears that when the oil is thick (cold) the pressure relief valve's passages are just not large enough to handle the flow so the pressure rises.

I've had my car since 1969 and it's always been the same - no seals have popped or other overload problems in just under 300,000 miles.

My advice (probably worth as much as you paid for it) is don't worry.

Regards,

Rojja