Hot tick over, throttle blip restores Oil pressure

[john c]

Oil pressure upon starting from cold with choke is 70+ on gauge, a stable tickover when warmed up, reads 40, if no traffic stops no problem. However, after an hour of use with regular traffic stops, the temp tends to rise, though the fan cutting in restores temp to just above normal, the oil pressure reads 65+ @2000, but if traffic persists, tickover oil pressure can fall to 5 or less. blipping the throttle will restore to 30. Getting back on the move will keep it above 50.

Starting up a couple of hours later, pressure is 30-40 at tickover and 70plus at 2000 revs.

I would appreciate your views on what may be need sorting?, thanks and regards, john

[Ian Vincent]

It sounds on the low side - could be the oil pump or the bearings on their way out. You could try using some 10w/60 oil (e.g. Mobil) and see if that improves the hot oil pressure, another solution, that is frowned on by many is to add some Molyslip to the oil.

 

Many years ago we took a friends MOT failure to the scrap yard but before we took it, we drained all the oil and ran the engine to see how long it lasted. (It had been treated with molyslip for a while before failing its MOT). It was amazing how long it lasted before it started rattling.

 

Rgds Ian

[McMuttley]

Hi John,

 

I have a very similar experience, eg, having to blip in traffic to get the pressure up and the red warning light out when hot.

 

Having raised the experience on here I have been re-assured that it is not unusual - albeit annoying, especially when you aren't on the level.

 

Like me have you learned to blip the throttle with the outside of your right foot when holding it on a downhill !

 

The advice i have been given is that hot oil thins and the pressure drops, but that its normal (ish)

[DaveN]

What car?

A couple of things, you don't have a separate oil feed to the rocker shaft do you? If so remove it!

Then dismantle the oil pressure relief valve clean it and the seat and refit. Possibly even replace the spring.

Idle speed correct?

Oil and filter old?

Failing that a nice job for winter. Check the crank end float is within limits and put a new set of shells in.

Having said that blipping the throttle restores it. Do you mean just a quick stab and then let it idle again and it settles down to 30 psi? If so I'd go for the pressure relief valve first!

[Steves_TR6]

I'm thinking pressure relief valve leaking myself.

 

Steve

[john c]

Thank you all for these responses, i had the engine rebuilt in 2007, 11k ago, i had a spin on conversion added, ill try a bosch oil filter and replace the relief ball valve and spring if they show wear or deformity. I always had some concern after the rebuild, so if the basics you suggest dont aleviate matters, i'll go for a pump rebuild and check the bearing end float as suggested.

I was also trying to reason why the pressure can be kept up if the revs are kept up?, thanks and regards, john

[john c]

Its a 4A, no separate rocker feed. I did invest perhaps in too much castrol classic oil?. The tick over starts off at 850, when just warmed up, then rises to 1000 to 1100, when hot, buts thats another problem,,,

[Ian Vincent]

The pressure stays up when the revs stay up by virtue of the pump pumping harder and trying to push more oil through the system. The gaps through which it's leaking away (irrespective of whether it's worn bearings or the relief valve not seating properly) remain the same size so the extra oil has nowhere to go and the pressure within the system rises.

 

Rgds Ian

[john c]

Thanks for that, regards, john

[Stanpartmanpartwolf]

There have been some pretty awful repro oil PRV plungers around that appear to have incorrectly angled or thin seats- these cause this very symptom.

As is often the case, an apparently worn OEM item actually performs better than a new pattern part.

Perhaps try an oldie before a fruitless engine strip & then go for oil pump next.

[BlueTR3A-5EKT]

There have been some pretty awful repro oil PRV plungers around that appear to have incorrectly angled or thin seats- these cause this very symptom.

As is often the case, an apparently worn OEM item actually performs better than a new pattern part.

Perhaps try an oldie before a fruitless engine strip & then go for oil pump next.

Good point. I had only considered 4 cyls which have the adjustable type with a ball bearing that forms the relief valve rather than the fixed pressure sping and plunger in the block that the 6 cyl (& Spit 4 cyl) use.

 

Peter W

[peejay4A]

It's a 4A.

[Stanpartmanpartwolf]

OK. I witnessed a TR4 with similar pressure problems once, that were traced to the oil PRV- there was a human hair trapped between the ball & its seat (missus).

[john c]

I bought a ball and spring from 2 different spares outlets, the balls were very close in size, but each spring was of a different length, one was canted slightly right after the short taper. Very helpfully checked all others in their parts bin, all faulty, refund given, The other is broad all its length. Will try it and see, wont get an opportunity until the weekend. Thanks and regards, john