Oil pressure warning light flickering when hot.

durneyj

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I'm fairly sure I know the answer to this, but I thought I'd ask in case I'm being dumb as a bag of hammers...

I've an 84ST and the the oil light flickers when the engine is very hot and it's on idle (bout 900 RPM) at traffic lights / junction or the like.

If i raise the revs to 1250, the flicker buggers off and all is well. Drop the revs and the flicker is back instantly.

It only happens if the engine gets really hot due to traffic / stop start driving for 5 or 10 minutes..

Once back on the open road and the engine gets a chance to cool, stopping at a junction does not bring the flickering light back.

The oil pressure switch was replaced recently as the old one was leaking. Unfortunately, I don't have a pressure gauge to have to verify that the pressure is dropping off when hot.

I will say that the problem was way worse on semi synth (put in at last service by reputable mechanic).

It did get much better when I started using 20-50 mineral oil and a Mahle filter.

I have no history on the bike and I reckon it had a harder life before I bought it and the speedo replaced at some point in the past, so no idea on miles.

Should I just park her up and talk nice to herself and the bank about funding a rebuild?

Am I missing something silly?

Opinions / ideas and suggestions gratefully received.

D

:beerjug:
 
The job of oil is primarily to lubricate the moving parts. Fully synthetic oil does that much better than mineral oil, especially when very hot. In a sense, effective lubrication is more important than oil pressure. Use fully synthetic of the recommended viscosity.

You say that you have just changed the pressure switch. Is that a clue to your issues?
 
I'm inclined to rule it out as the flickering happens only when the engine is really hot. If the switch was dodge.. I'd be expecting more erratic behavior of the light.. however, I'm going to replace it with an OEM one ASAP.

I've sourced an oil pressure gauge and sender. I'm going to give that a shot also.

As to synthetic / semi / mineral, I'm not so sure about using fully synth in an airhead. Any reading I've done suggests they might not work well in the older engine. Open to correction tho.
 
Fully synthetic is much much better for air cooled engines which run at higher temps than water cooled engines.

Why wouldn't you use it?
 
Two things that spring to mind straight away and are fairly easy to check.
Incorrectly fitted oil filter o ring/shim or oil filter canister has sunken into casing.(this could be rectified by fitting more shims)
Oil pressure relief valve sticking open or debris stopping it closing off.
To check this requires the front cover off but better than an engine rebuild.
The oil pump on an airhead is pretty good ,
I’d get hold of a pressure gauge if poss to get some decent readings for comparison as you check and rectify.
Whilst I don’t like to disagree with anyones opinion an airhead is happier on a 20/50 mineral “ classic” oil.
 
Could you use a thicker oil? Would that have an effect?
 
That sounds like something I can do. I replaced the timing chain a couple of months ago.. it was pretty rattly..

Inside the timing chain case was pretty clean, but that doesn't mean too much, I suppose.

I've really no idea what the engine has been through history wise.

I'll take the oil pressure readings first and get a base line. It the pressure is low, I'll pull the cover and check the pressure relief valve. While I'm at it, I'll change the filter and check o-ring.
 
A good oil pump would easily exceed 80 psi pressure on a cold motor,this is enough to open the pressure relief straight away.
If you crank the engine with the plug caps off till the light goes out,it should take a good few seconds before the light comes back on.
A rebuilt motor on a cold day would prob take 20 seconds +.
Hence the need for a gauge.
If the pressure drops off straight away.
The motor is dumping pressure ,either from the oil filter canister,
The oil pressure relief valve,or worn crank bearings.
The above two are easy to check
 
Thanks Mikey..

Cranking from cold, light goes out straight away, but is back on after 5 seconds...
 
Mad Hatter said:
I would definitely check your filter canister depth before doing anything else. You need 3.3-3.7mm depth. Full details here http://www.largiader.com/tech/filters/
Click to expand...

Thanks. I'll double check that. I'm pretty sure there's no shim in there at the minute.

[Edit] Reading these articles makes me think i misinterpreted whether the shim was needed or not. Here's hoping i haven't bollloxed things up...
 
durneyj said:
Thanks. I'll double check that. I'm pretty sure there's no shim in there at the minute.

[Edit] Reading these articles makes me think i misinterpreted whether the shim was needed or not. Here's hoping i haven't bollloxed things up...
Click to expand...

You really need to measure the depth accurately to be able to work out what combination of shims/gasket is required, you can’t guess at it
 
Air cooled engines of the this age were not designed to run on synthetic oils due to the larger engine clearances because of heat, a good quality 20/50 mineral as Mikey says is what it needs.
 
Mad Hatter said:
You really need to measure the depth accurately to be able to work out what combination of shims/gasket is required, you can’t guess at it
Click to expand...

I’ll measure it with the vernier and make sure that right. Thanks for the comments and help. I’ll let you know what I find.
 
barny said:
Air cooled engines of the this age were not designed to run on synthetic oils due to the larger engine clearances because of heat, a good quality 20/50 mineral as Mikey says is what it needs.
Click to expand...

Yet Castrol recommends Power1 4T 10w-30 - a fully synthetic oil for the '84 R series.

But what do they know?
 
durneyj said:
Ahh, I think my problem is more to do with wear and abuse than oil Nin. If there was molasses in the sump, the light would still flicker :-D

Ya live and learn.
Click to expand...

Sorry that wasn’t directed at you! Others can’t resist though. Good thing it’s not a ‘how to strap your bike to a trailer’ or I’d be in there myself!
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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