Oil filter light suddenly came on

[DRMM]

Hi guys,
I was happily going along and suddenly the oil filter light came on (whilst driving). The oil pressure sensor in the back of the block seems to be working ok still, it's just the filter sensor indicator.
So, I did the obvious - changed the filter and oil... But the filter light still stays on!
I don't know if I should worry or not (if I understand correctly the spin-on filters don't have a sensor anyway? Mine is the paper type; not the spin-on).

Could someone clarify the workings of the oil flow? I'm presuming the oil is sucked up by the pump and then pumped past the block pressure sensor to the filter [and filter sensor], through the filter to the engine where it does its job.
So, if that is correct, if there is a blockage at or in or beyond the filter then the main pressure sensor would indicate that all is well still (cos good pressure at that point), but if there is a blockage (or blocked filter) then it would not be well actually? Thus the sense of a filter sensor, hey?
Do the filter sensors sometimes fail? Could my case be simply a sensor fail?
Is there something I can do to test if the oil is actually flowing through the engine or not (I don't have a pressure gauge btw)? Would it be safe to start the engine with the rocker cover removed, to see if oil is getting up there? If so, how much oil should I see squirting around there at tick-over?

Or should I just not worry, as the main pressure sensor indicates well enough?

Cheers guys.

[simmitc]

The blocked filter light was fitted in very limited numbers. Given how wiring can be muddles over the years, the first check is to make sure that the light coming on really is the blocked filter warning. Disconnect the wire from the switch on the filter head. Check that the light has gone out (when it's beene on). Earth the wire and confirm that the light comes on. Once we know that it's definitely the filter warning light then we can go from there.

[DRMM]

... thanks simmitc...
I did already try disconnecting the wire from the filter head and the warning light does indeed go out.
I didn't try contacting it to the block though... what would that tell me?

[DRMM]

... I just came across this in a different post:

"...and make sure the rubber o ring is in the filter sealing the plate to the bolt"

When I changed the filter I didn't see any o-ring between plate and bolt! Could this make the difference?

[philthehill]

Here is a link to the MOSS parts list showing the oil filter parts.

https://www.moss-europe.co.uk/shop-by-m ... minor.html

You can check what you have and the way it is assembled against the parts list.

The blocked oil filter switch is activated when a difference in oil pressure is detected between the outside and inside of the oil filter element. Oil but with a restricted flow will still pass through the filter and the bypass valve. The light tells you it is about time you changed the oil filter. BMC/BL latterly did away with the switch and function.

There is always a small amount of oil passing through the filter head bypass valve so not all oil passing to the bearings is filtered. The only way to get fully filtered oil to blank off the bypass valve. A unmodified bypass valve is shown in the photo below just left of the filter screw on/off boss.

filter head 1.JPG (1.42 MiB) Viewed 1698 times

If there is an increase in oil pressure before the oil filter but after the bypass valve is blocked oil will be directed via the oil pressure relief valve back to the sump.

[DRMM]

...Thanks for that Phil.

From that parts list diagram it seems I didn't fit/refit the "sealing washer" between the pressure plate and the "plain washer". (it's possible I didn't notice it fall out into the oil drain tray when I removed the bowl etc.!).
Not sure what the effect of that would be though?

And the pressure plate - is it correctly fitted with the outer cupped rim facing away from the paper element (mine was/is)?

I still need to get my head round how the "filter blocked" switch works. Should the warning light be on or off with the ignition on but engine NOT running? Obviously it should be normally off when the engine is running.

Cheers

[philthehill]

Having the sealing washer in place is better but it is not the end of the world if it is not in place.

The plate should be fitted with the domed centre upwards. The dome fits into the bottom of the filter element.

The warning light should be off if the switch is not activated.

Just think of the switch as a means of determining if there is a difference in pressure between the outside and inside of the oil filter element.

[DRMM]

Just think of the switch as a means of determining if there is a difference in pressure between the outside and inside of the oil filter element.

Ok that sounds easy...

... I'm more worried now though - since opening the oil filler cap with the engine ticking over - there's no oil squirting around as far as I can see, and not really a coating of oil which I would've thought there would be.

So to recap: the oil filter warning light comes on when the ignition is switched on (you're saying it shouldn't), and it stays on when I start up the engine (which it obviously shouldn't).
But the oil pressure warning light seems to be indicating okay (it goes out when the engine starts up).

What to do now?
Are there any checks that I could do to ascertain if there is a block beyond the filter (as I've already changed the filter element)?

[paul 300358]

If your worried look at fitting a oil pressure gauge, simple to do and there are plenty of posts on here which cover it

[DRMM]

If your worried look at fitting a oil pressure gauge, simple to do and there are plenty of posts on here which cover it

Thanks Paul. Will it tell me anything more though, as it would be fitted at the oil pressure switch position which at the moment seems to be indicating things are well enough (according to the oil pressure warning light) at that point?

Do you know, should I be seeing oil splashing around in the rocker box?

[philthehill]

If the oil blockage light stays on when the engine is running then you do need to change the oil filter.
The oil pressure warning light only comes on when the oil pressure is below 15lb/sq in - so is no real indicator of the oil pressure circulating through the oil galleries.
There should be oil visible on and around the rockers when the oil filler cap is removed when the engine is running.

Change the oil filter and see what happens.

If the light does not go out when a new filter is fitted it could be a faulty blocked filter switch but I would want to know what the oil pressure is when it circulates through the galleries and the only way to confirm the pressure is to fit an oil pressure gauge.

[DRMM]

If the oil blockage light stays on when the engine is running then you do need to change the oil filter.
...
Change the oil filter and see what happens.
...

I have changed the oil filter, Phil. It was the first obvious thing to try, but it didn't cure it, which is why I'm worried.

...The oil pressure warning light only comes on when the oil pressure is below 15lb/sq in - so is no real indicator of the oil pressure circulating through the oil galleries.
...

... Okay, so if I fit a gauge and it reads in spec does that mean I don't have to worry about it more? ie if it's in spec it means no blockage?

[DRMM]

... Ah, just thought - could it be that after I changed the filter and oil, remnants of crud from the sump re-blocked the new filter? The oil was pretty bad looking.

[DRMM]

...
There should be oil visible on and around the rockers when the oil filler cap is removed when the engine is running.
...

This is why I'm worried because there is not oil there. At least not what I'd expect. In fact it looks rather dry!

But anyway, I'll look at fitting an oil pressure gauge.

[philthehill]

Fit the oil pressure gauge and see what the oil pressure is in the galleries. please post the readings on this thread.

If there was quantities of crud in the sump it may well now be blocking the oil filter element.

There should be signs of oil on or around the rockers with the engine running. If not the flow of oil may be restricted by a blocked oil filter.

The blocked oil filter switches are fairly reliable though the early type with a detachable housing on the filter head were suspect.

[DRMM]

... Okay, thanks again Phil.

[paul 300358]

If the oil was old, I would change the oil and filter again after a good run.

[DRMM]

If the oil was old, I would change the oil and filter again after a good run.

Yes, the oil did look old. I bought the car not long ago and was told it had been sitting in a garage for some years before that.
So yes, maybe worth trying a second change of filter & oil.
Is it much of a job to remove the sump (to clean out any remaining crud)?

[paul 300358]

Its a fairly easy job to remove the sump provided you take your time, you will need a tub of grease, a 7/16 AF socket and extension, a sump gasket set with cork seals, a sharp knife to cut the seals to the correct length, a jack and axle stands and a good work light. If you have a search there was recently a lot written on removing and replacing the sump. You may be worrying unnecessarily, I would remove the rocker cover, start the car and see if you get oil to the rockers. If you do, replace the cover and run it a bit then change the oil again.

I've probably forgotten something above, someone will suggest a few more necessary tools soon.

[DRMM]

Its a fairly easy job to remove the sump provided you take your time, you will need a tub of grease, a 7/16 AF socket and extension, a sump gasket set with cork seals, a sharp knife to cut the seals to the correct length, a jack and axle stands and a good work light. If you have a search there was recently a lot written on removing and replacing the sump. You may be worrying unnecessarily, I would remove the rocker cover, start the car and see if you get oil to the rockers. If you do, replace the cover and run it a bit then change the oil again.
...

Thanks for that Paul - good to know exactly what's needed before starting.