Oil light on when warm

Tips and help requests for your cars mechanics. points gaps, timming settings all those sorts of things

Oil light on when warm

Postby reb78 » Sat May 11, 2019 5:49 pm

We got the magnum started for the first time in four years today so I can get her on a trailer and transport to my workshed so the rebuild can commence.

The oil light is coming on when warm. Its the 1800 engine. I have tried an oil change with the correct spec oil but no change.

Pressure switch, then pump, then big end bearings are my first thoughts. What else could it be and how should i diagnose?
reb78
SL Viva
SL Viva
 
Posts: 75
Joined: Thu May 03, 2012 2:59 pm
Location: Hertfordshire or Kent

Re: Oil light on when warm

Postby droopsnoot » Sat May 11, 2019 6:37 pm

Can you get hold of a capillary pressure gauge, similar to the one fitted in the seven-dial dash? They have an adapter that sits between the block and the pressure switch and takes a pressure pipe to the gauge. I had a flickering pressure light a while back on the Firenza, and the pressure gauge was the thing that kept my sanity. For me, swapping the low-pressure switch sorted the problem out. But the first thing is, find out whether you've got a pressure problem, or a pressure indication problem.
My real name: Mike. My web site: http://www.firenza.net

My stuff for sale: http://www.firenza.net/forsale.shtml
droopsnoot
Old Nail
Old Nail
 
Posts: 2302
Joined: Mon Oct 31, 2005 2:08 pm
Location: Cheshire

Re: Oil light on when warm

Postby rizzo » Sat May 11, 2019 8:29 pm

If you get to the point that your thinking pump or bearings, DON'T fit the pump first, look at the bearings first after checking your pick up strainer, its not common to have a pump issue with out worn bearings all your likely to do is damage the replacement pump.
HB 1159 1968 10K White
HB 4000 1968 Green
User avatar
rizzo
Baby Bertha
Baby Bertha
 
Posts: 1011
Joined: Sun Nov 09, 2008 10:43 pm
Location: North Yorks

Re: Oil light on when warm

Postby 1972nail » Sat May 11, 2019 9:21 pm

I agree with droopsnoot (Mike) The pressure switches are cheap and worth changing just in case. The oil itself could well be the problem. The slant 4 puts out a lot of heat and modern formulae of 20/50 will not hold up very long to the extremes of temperature.

Modern mineral oils have a much lower shear resistance than their ancestors, mainly due to the need to reduce emissions of the deadly additives. Once the shear temp is reached the oil never recover it's original viscosity, and the shear temp is lowered, this is than a downward slope eventually to oil pressure problems when the oil is hot.

You really need a semi synthetic with ZDDP additive these have a much higher shear resistance than mineral oils. You can than be sure that the oil does not reach it's shear temperature.

I had the same problem with my 2300, a modern high quality classic blend 20/50 mineral oil would fail after only a few hundred miles. I did a lot of research and asked lots of questions from oil manufacturers and blenders. From their recommendations I decided to use Millers Classic Sport 20/50 Semi Synthetic and have not had any problems since.

Have a read at this post.

viewtopic.php?f=289&t=26312&hilit=shear
Editor of the VVOC Magazine ReVival

"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.
User avatar
1972nail
Old Nail
Old Nail
 
Posts: 3342
Joined: Sun Aug 07, 2011 4:16 pm
Location: Ballymoney Co Antrim - some say....the World's best place to live!

Re: Oil light on when warm

Postby 1972nail » Sat May 11, 2019 9:32 pm

I've just read your previous post from 2014 about the same problem. viewtopic.php?f=14&t=24183&hilit=shear

Could well be the 'O' rings that seal around ports of the pump to the block. If the engine has been sitting for a long time these may have lost their ability to seal.

Having said that, I put the engine currently in my car into storage in 1983 and it wasn't started again until 2014 and it built pressure immediately. I fitted it to the car and it's been there ever since without any problems. However after a very few miles the oil light came on continuously. I had the luxury of a pressure gauge in the 7 dial dash and it showed very good pressure. A swap to a new switch fixed the problem.
Editor of the VVOC Magazine ReVival

"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.
User avatar
1972nail
Old Nail
Old Nail
 
Posts: 3342
Joined: Sun Aug 07, 2011 4:16 pm
Location: Ballymoney Co Antrim - some say....the World's best place to live!

Re: Oil light on when warm

Postby reb78 » Mon May 13, 2019 10:10 am

Sorry about that, I forgot I had posted all that time ago.

I was trying to get my father involved in a restoration of the car back then but his health meant that it didn't happen. This weekend though we got her started and she is now in my workshop on the ramp.

I would like to diagnose the oil pressure issue then remove the engine so that i can crack on with the bodywork - my initial plan was to run the engine until it needed work (as it was always mechanically pretty good), but if this turns out to be a pressure issue then I can go deeper into an engine rebuild whilst the lump is out.

When loading on the trailer on Sunday, the oil light didn't go out at all. Engine didn't sound bad. I have a new switch so will try that and see if I can get hold of a pressure sender and gauge - any ideas on an easy place to locate one?
reb78
SL Viva
SL Viva
 
Posts: 75
Joined: Thu May 03, 2012 2:59 pm
Location: Hertfordshire or Kent

Re: Oil light on when warm

Postby 1972nail » Mon May 13, 2019 5:14 pm

You'll need an adaptor to allow the gauge and electric sender to be connected at the same time. The classic Mini used the same adaptor so that may be your best bet. The Classic Mini also used a Smiths oil pressure gauge and again that will be suitable, than all you will need is the capillary tube from a Mini again to complete the setup. I would guess that there will be a few secondhand on eBay. Buy it all cheap enough, use it to diagnose the problem and then sell on again when no longer needed. :goodideasign:
Editor of the VVOC Magazine ReVival

"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.
User avatar
1972nail
Old Nail
Old Nail
 
Posts: 3342
Joined: Sun Aug 07, 2011 4:16 pm
Location: Ballymoney Co Antrim - some say....the World's best place to live!

Re: Oil light on when warm

Postby reb78 » Tue May 14, 2019 10:43 am

Thanks for that - i will take a look for the bits.

I fitted a new pressure sender yesterday and the light seems to be behaving as it should now - on with ignition and off after that and stays off!

I will try to locate and fit a pressure gauge though so that we really know what is going on.
reb78
SL Viva
SL Viva
 
Posts: 75
Joined: Thu May 03, 2012 2:59 pm
Location: Hertfordshire or Kent

Re: Oil light on when warm

Postby 1972nail » Tue May 14, 2019 11:11 am

reb78 wrote:Thanks for that - i will take a look for the bits.

I fitted a new pressure sender yesterday and the light seems to be behaving as it should now - on with ignition and off after that and stays off!

I will try to locate and fit a pressure gauge though so that we really know what is going on.


That sounds like you had a dodgy sender. The rubber diaphragm in them gets perished and fails over time.
Editor of the VVOC Magazine ReVival

"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.
User avatar
1972nail
Old Nail
Old Nail
 
Posts: 3342
Joined: Sun Aug 07, 2011 4:16 pm
Location: Ballymoney Co Antrim - some say....the World's best place to live!


Return to Mechanical

Who is online

Users browsing this forum: No registered users and 0 guests