oil Pressure readings

Post by **zippy500** » Fri Jul 21, 2006 8:40 pm

I have fitted a capillary oil pressure gauge.

On starting up from cold i am reading 55.

Can anyone tell me what reading I should be looking at cold/hot.

Thanks

Post by **Willie** » Fri Jul 21, 2006 9:27 pm

the designed maximum pressure is 60 lbs and on a good engine this will be
the reading at anything over 30 mph in top gear HOT. The tickover pressure
would be 40 lbs hot on the same good engine. The MAXIMUM pressure is
controlled by the Oil Pressure Relief Valve which is situated under a domed nut to the rear of the distributor. The length of the spring under that domed
nut is critical i.e. it should be 2 55/64" or 72.63mm. If it is shorter the max
pressure will be lower. If it is correct but the pressure is lower then either
the bearings are worn, or the oil pump is below par but, the engine will work
happily for many thousands of miles if the pressures are not at the optimum.
Unfortunately, it is necessary to unbolt the starter motor so that it can be swung out of the way to enable a large socket to undo this domed nut.

Post by **bmcecosse** » Sat Jul 22, 2006 9:44 am

Your cold pressure seems a bit low - most will go up to ~ 70 psi cold although as Willie says - 60 is the standard relief valve setting. Hot pressure is what matters - 10 psi per 10 mph in top gear is about thje minimum acceptable - up to 60 obviously. New engine will be 60 psi at anything above idle. The relief valve can be accessed without moving the starter.

Post by **MikeNash** » Sun Jul 23, 2006 9:23 pm

My 1098 is what I call loose but good in that it gives around 60 psi cold and 40 psi when hot at around 50-60 mph, cruising easily at 60-70 mph, and having 10-15 psi when idling ie the slowest reliable idle I can get.
I'd say that if you've no nasty noises then don't worry. Your ears will tell you if you've real trouble. Regards, MikeN.

Post by **pim123** » Sun Oct 22, 2006 2:30 pm

Mine is reading 25 when running idle and 50/55 when running at 70 km/h. The car just had new head gasket set put in. Engine running fine, oil level is ok, no strange noises, no excesive oil leakage.
Should I worry or check anything ?

Post by **Onne** » Sun Oct 22, 2006 2:49 pm

Well. some of you may know my engine (website rally people

)
My oil pressures:
when cold, doing 40mph : 70psi
when hot, doing 70mph: 40 psi at most, usually 35-38psi
when hot and idling: (800rpm) 6-8 psi (light comes on), I set my idle to about 1000 rpm, and then have 11 psi.

My engine is quite dead though, only runs properly on 2,5 cylinders....

Post by **bmcecosse** » Sun Oct 22, 2006 9:31 pm

I wouldn't worry about it - it's not a racing engine! You should use 20W50 oil for best results on these older engines.

Post by **Axolotl** » Mon Oct 23, 2006 12:10 am

Workshop manual for 1098cc engine gives 15 psi as minimum idling pressure (hot), 60 psi normal running. (Fat chance).

The oil pressure warning light should come on at 8 psi if it's working right.

In practice, anything between 40 psi and 60 psi in normal running (hot) won't be a problem. 70 psi suggests a) the gauge is inaccurate or b) the pressure relief valve is stuck.

The behaviour of the gauge is more important than the actual pressure reading (as that is affected by the gauge calibration if capilliary or the voltage and gauge calibration if electrical).

A regular "beat" on the gauge can indicate worn big ends, general low pressure is worn main bearings and/or oil pump.

Let's face it, without the gauge, anything above 8 psi is acceptable!

Post by **bmcecosse** » Mon Oct 23, 2006 9:45 am

When the oil is cold the relief valve can't cope - and so the pressure goes high. Just ignore this - it's the hot pressure that matters. Around 10psi per 10 mph in top gear is not too bad for a 'road' engine.

Post by **PAULJ** » Wed Nov 08, 2006 6:27 pm

can anyone tell me how I fit a oil pressure gauge to a 1275 engine.I want to fit an electrical one. where do I get a sender from.
Thanks

Post by **rayofleamington** » Wed Nov 08, 2006 7:11 pm

When the oil is cold the relief valve can't cope

??
The viscosity of the oil is higher when cold therefore the valve will need to open further for the same amount of flow. Opening further is the reason for the higher pressure - I've never come across a spring-closing relief valve that operated differently.
When the oil is at normal operating temperature you shouldn't find much above 60 - 65 psi. If it is higher then your relief valve is incorrect.

Pressure at idle when hot is the most obvious sign of a half dead engine - if it's down below 10psi then things are not healthy.

Post by **Kevin** » Thu Nov 09, 2006 11:05 pm

can anyone tell me how I fit a oil pressure gauge to a 1275 engine.I want to fit an electrical one. where do I get a sender from.

I dont think such a thing exists all the gauges I have seen have either a metal or plastic feed pipe to the gauge like this
http://morrisminorspares.co.uk/shop/ind ... d7772a7b90

Post by **Alec** » Fri Nov 10, 2006 8:33 am

Hello Kevin,

sorry to contradict, but Jaguars for one have used a purely electrical pressure gauge with a transducer fitted to the block. Various after market suppliers also do them, I have one on my Triumph as a fuel pressure gauge (p.I. system) but I can't remember the name of the supplier. E. Bay is worth a look.

Alec

Post by **Axolotl** » Fri Nov 10, 2006 8:36 am

They certainly do exist. (Electrical oil pressiure gauges) My car has one, and so does my boat. Less risk of ending up with a lap full of oil when the pipe becomes detached.

I'll have a poke round later and find some sites that sell them, and the senders.

Post by **Axolotl** » Fri Nov 10, 2006 8:42 am

Go to www.burtonpower.com and search for oil pressure.

That lists the sender and various gauges, electrical and mechanical. Some come complete with sender. Their site has a lot of other useful adapters and T-pieces.

Or try www.demon-tweeks.co.uk and search for oil pressure sender. Don't be put off by the price of the Smiths ones.

You'll also need a T-piece if you want to retain the oil pressure warning light.

Post by **Roni** » Fri Nov 10, 2006 8:53 am

I have an electrical one on mine by the brand of AutoGauge. The sender, though, is quite a bulky item and only just fit on a 1098.

Post by **Kevin** » Fri Nov 10, 2006 4:14 pm

Well Alec I obviously dont drive in the same quality of car as you

But seriously on the Demon Tweeks site the sender alone is £28 although I found a guage for £30, both + vat and this one was in Lbs but most are in Bar`s

Post by **PAULJ** » Sat Nov 11, 2006 5:56 pm

Thanks all, demon tweeks have the lot. i've only had the car a week and I knew I should have some indication of oil pressure (a light at least). One last stupid question, Is the T piece metric or imp

Post by **Axolotl** » Sun Nov 12, 2006 12:09 pm

The thread in the block is imperial, so an imperial T-piece will do the job between the existing oil pressure switch sender and the block.

I think the pitch of the imperial and metric taper threads is the same, and as they are tapered, the new sender will screw into the imperial T-piece, even if it actually has a metric thread.

Make sure you don't overtighten them, as it is easy to split the brass t-piece. I found a bit of PTFE tape wrapped round each male thrread gave a good oil tight seal with minimal tightening.

Post by **badfelafel** » Wed Nov 15, 2006 4:14 pm

I'm glad someone asked about oil pressure gauge readings... mine was fluctuating wildly, now always reads zero. But the car runs fine. Any chance its just the gauge? Hope so, or something bad might be happening!!!