Oil light flicker

[gung]

Hi
I've only had my Fastback (1967) for 3 weeks - she is great tho!
I have noticed that when the engine is warmed up that the oil light on the dash comes on or flickers at about 1000 rpm but goes out again when you speed up past 1500rpm - Just wondered if anyone has any ideas what's causing that?
cheers
Angela

[miketyp3]

Hi Angela

I'm afraid it does sound an awful lot like a classic symtom of a worn engine...

There's a few other things worth checking first though.

Old or wrong type of oil - You say you've only had the car 3 weeks... so do you know when it last had an oil change and what oil has been used?
Oils designed for modern cars tend to be too thin for our engines.
I always use SAE 30 monograde, just because it was what the engine was designed for, but there are multigrades you can use & some people prefer them - stick to something like a 20/50w though.

Old oil, apart from carrying all sorts of rubbish around the engine, will loose some of its viscosity.
If you haven't already I would recommened an oil change (& don't forget to clean the filter) I'd do it anyway even if the seller told you it has been recently done.

Fuel in oil - the same sort of effect, a leaky fuel pump diaphram will drain petrol into the sump diluteing the oil. This will then become too thin to be pumped properly - I know... it happened to me!

Check your oil level is not rising (not always evident if the engine leaks anyway) and smell / feel the oil - you'll need to repair or replace the fuel pump if you think it is at fault.

Faulty pressure sender - For what they cost and if it's not any of the above then its worth trying a new one. Personally I've never had one fail and I would have thought the warning light would be either perminantly on or off, but you never know...

Worn or bowed oil pump cover - A common fault that can eventually lead to low oil pressure is the steel cover plate on the oil pump becomes bent through over tightening or scored with use.

You can flatten the plate by sanding it using a sheet of P240 wet & dry on a piece of thickish glass (plain of course).
Places that cut glass to size often have small offcuts they will give you - ask them very nicely and they may grind the sharp edges off as well!
Use a little light oil (eg 3 in 1) on the wet & dry to stop it from clogging.
The cover plate is between the fan shroud and the engine and retained on studs, so tricky to get off without droping the engine and removing the fan first.
If you can get the pump out as well then its worth flattening the mating face on the body in the same way - for referance the gears & the outer face of the body should be flush, so sand the body with the gears in - the gasket thickness then creates the running clearance it needs.

Others may disagree (they usually do!) but I wouldn't panic too much just yet... As long as the light goes out when you blip the throttle like you say then its not going to let you down for a while. Just bare in mind if its not an easy fix then the engine could probably do with a rebuild before too long.

Mike

[purplepeter]

Does it do that all the time Angela? Or just most noticeably when you first run the engine each time?...I'd be inclined to drop the Pressure relief/bypass valves out when you change the oil,& get rid of any sludge.

[gung]

Hi Guys
I have no idea when the oil was last changed - so seems sensible to do an oil change ASAP.
Will work my way though the possibilities suggested & let you know how I get on.
thanks
Angela

[broady_6]

I had a similar problem in the not too distant past. It turned out that after sending my block away to be machined a dowel peg had not been replaced and the rebuilt engine had a crank bearing which wasn’t secure. The result was low oil pressure when the engine was warm at low rpms. I appreciate this is a rare and extreme situation but at the same time it’s an inexpensive fix

[Editor]

Just one addition - check the oil level. the engines don't have all that much oil compared with some cars, so it is vital to make sure you don't let it get low. Somewhere between the two marks on the dipstick is OK, but not below.

Another indication of a worn engine is to listen carefully when you start it. Is there any sign of a knocking sound which quietens and goes away after a few seconds. That can help diagnose a worn engine.

Also make sure all the cooling air is reaching the engine - sometimes people leave the elbows off the fan housing after removing heater pipes etc, or putting on a non-stock exhaust. Overheating will thin the oil, which is bad for the engine.

[gung]

Hi All
I have had a good look/smell & check of the engine & oil. It has enough in & it doesn't smell of petrol.
What I did notice was this


The plastic cap on the oil breather seems to be mis-shped (possibly melted!) & it has a hole in the top, also the spring underneath the cap is missing! might this be the cause of my problem?
There is also a very small amount of oil leaking from the sump coverplate & also from one of the rocker covers.

[miketyp3]

Mmmm, my guess is the cap has been melted & drilled and spring removed all to prevent it from being blown out by excess crankcase pressure - usually due to blow by through worn cylinder bores / piston rings.
Unless they made it clear it sounds like whoever sold it to you has been fairly unscrupulous, I do hope it wasn't off this forum...

As long as there's enough oil in and its in good enough condition then it's not going to cause the flicker.

Leaking rocker cover seals & sump covers are just other indicators of poor maintanance.

Sorry, but it does sound an awful lot like it needs a rebuild.

Mike

[type3]

It does sound like rebuild time. Also check that the oil cooler isn't blocked with crud as that'll cause it overheat and flicker.

[Editor]

The rocker cover is probably just a matter of fitting a new gasket.

The breather cap might have been fitting poorly - the lugs that hold them on do tend to suffer with time, and may need putting in boiling water then spreading a bit to grip, but you need another cap and spring for that.

When you change the oil, remove the slump plate and use a new gasket set. If the nuts on there are not acorn type (ie seal their threads), that might be why there's oil around there. Clean off the oil on the sump and try to see where it's coming from, if it still leaks some.

[ghia n square]

I agree with the the above. Change the oil and add a fortifier first off. Make sure the timing and mixture are correct because if it's running hot it can bring the light on. Give it a service and use a fuel additive. Bin the pancake air filters if you are using them alternatively check the oil level in the standard air filter and make sure all the connections are good. If nothng works just drive it until dies then it's rebuild time