Thornycroft BMC 1.5 Oil Pressure Query.

[austinlegro]

Odd question with possibly just not quite enough data to answer.

The engine has been well used, burns a little oil and leaks a little oil but has generally good oil pressure albeit with a quite agitated gauge needle.

A friend borrowed our boat and reported that the warning buzzer sounded and the oil pressure was low towards the end of a day's cruising.

Adding oil cured it but 'not completely'

My wife took it out for a cruise last weekend, she checked the oil, cruised, and had the warning buzzer / low OP late in the day. She added what oil she could find (not very much) without checking the level at the time or even when returning to the marina.

Water temp remains fine.

Adding the oil made the warning beep 'slightly muffled'?

So, wearing my Sherlock Holmes hat, my friend added enough oil on the previous cruise such that the level was fine when my wife took it out.

The low OP is therefore not caused by lack of oil, neither is it simply when the engine / oil is warm.

The problem only happens after a full day's boating but is not but i don't think because of oil depletion.

I've ordered a new pressure relief valve and spring but not totally convinced that's the issue.

It's not easy to diagnose without running the motor for a day!

Anyone experienced anything similar?

Time related OP sender weirdness possibly?

 

[Tony Brooks]

First of all you really should do a pressure check with a mechanical gauge fitted otherwise you are fault finding by substitution and that becomes expensive.

My first thought in this kind of case as the gauge still showed perhaps 30PSI plus at the end of the day and revving would be a faulty oil pressure switch, the one that works the light. They are not the most reliable of things. It will be a standard BMC vehicle switch so should not be very expensive.

[bizzard]

Here's a big wheeze of the week.  If you can fit one of these you could check the oil pressure with an old fashioned sliding type tre pressure gauge or even boost the oil pressure with a little 12v electrick tyre pump that plugs into a fag lighter socket. Most of these also have a prssure gauge.  Remove oil pressure switch to fit the Schrader valve to do the test, remove it afterwards and refit the sender.

  Thread size is 1/8'' NPT      Is that good.   

Edited October 17, 2019 by bizzard