oil light flicker at 3.5k rpm.....

Will Reeve · Post by **Will Reeve** » Sat Jul 31, 2010 4:12 pm

400miles into the running in period. Just blipped to 3.5k rpm in 2nd gear and the oil light flicked on for a fraction, just a flicker. I though I was imagining it but it's happened both times I've revved that high.
While stationary you can blip to 4k and nothing happens.
Ideas? Oil pressure relief valve? Sump oil is about 10mm over the "full" line on the dipstick. I though that would be OK until the 500 mile oil change? As you can imagine I am worried now!

JP. · Post by **JP.** » Sat Jul 31, 2010 4:56 pm

What does the oil pressure gauge say............
Or do you only have an idiot light?

Ian Anderson · Post by **Ian Anderson** » Sat Jul 31, 2010 5:53 pm

Is your dipstick level correct?

I heard a Ford 302 that was "overfull" went to change oil and onlu had 2 l in the sump

Dip stick was not calibrated.

So in this case a hard run would / could end up pumping all the oil to top of engine and allow it to suck air

Ian

Will Reeve · Post by **Will Reeve** » Mon Aug 02, 2010 6:43 pm

Hi guys, I poured in at least 6l of oil after the rebuild with no leaks so I hope it's all in there. Good point about the dip-stick. It's not standard, but a chrome shiny one! I think I better measure how far it goes into the sump!

There is a pressure sensor sender by the oil pump, with a single 1/4" spade terminal on it, it's not used as I don't have a pressure gauge. I think I need to invest in one. I presume it's a standard SD1 sender, anyone know what the dial required for it is? Or can I just use a multimeter for a quick check? Does it's resistance change with pressure?

ian.stewart · Post by **ian.stewart** » Mon Aug 02, 2010 7:05 pm

Do you have a modified sump?? has the sump been bottomed out?, Dont suppose the light is flickering when braking?? could be the sump needs baffling, and if its modified could mean the strainer is stuck to the bottom of the sump, but my favorate would be the old chestnut, Sticky Releif valve, cheap repair woukd be fit a Tadpole valve

DaveEFI · Post by **DaveEFI** » Tue Aug 03, 2010 7:01 am

Will Reeve wrote:Hi guys, I poured in at least 6l of oil after the rebuild with no leaks so I hope it's all in there. Good point about the dip-stick. It's not standard, but a chrome shiny one! I think I better measure how far it goes into the sump!

There is a pressure sensor sender by the oil pump, with a single 1/4" spade terminal on it, it's not used as I don't have a pressure gauge. I think I need to invest in one. I presume it's a standard SD1 sender, anyone know what the dial required for it is? Or can I just use a multimeter for a quick check? Does it's resistance change with pressure?

The SD1 gauge is part of a group - although it could be removed and used standalone. But would not look good. Nor is it known to be accurate. Better to fit a complete aftermarket one.

Will Reeve · Post by **Will Reeve** » Tue Aug 03, 2010 11:58 am

Hi, where can I get a tadpole? On the rebuild I took the pressure release apart and polished, there was a little scouring, but it seems to fit the bore quite well. I think I lubed it with some grease. I think I will pop it out and see what it looks like.

ian.stewart · Post by **ian.stewart** » Tue Aug 03, 2010 12:13 pm

Think Real Steel sell them, another thought, what oil are you running?? I assume we are talking about a 3.5 or 3.9 and not the X bolted engine?? as they use a different type pump, the earlier engine MUST be run on 20/50

Will Reeve · Post by **Will Reeve** » Tue Aug 03, 2010 12:26 pm

Running 20W50 classic "light green" Comma oil. Pressure light goes of almost instantly on cranking (but that is with a fast starter motor!). She has a dizzy run oil pump.

DaveEFI · Post by **DaveEFI** » Tue Aug 03, 2010 1:25 pm

ian.stewart wrote:Think Real Steel sell them, another thought, what oil are you running?? I assume we are talking about a 3.5 or 3.9 and not the X bolted engine?? as they use a different type pump, the earlier engine MUST be run on 20/50

Err, my '84 SD1 EFI has done over 160,000 miles on only 10/40, as per the handbook.

JP. · Post by **JP.** » Tue Aug 03, 2010 3:15 pm

Err, my '80 3.5 SD1 engine in the Capri is running on 15W40 for years now without any issues.
The lifters didn't like 20W50.............. and yess my handbook says also 10W40.

Well if the pressure relieve valve is stuck open you could have this problem. If its stuck closed you would burst your oil filter ( 20+ bar).

I'd say check this valve for free movement and get that oil pressure gauge ASAP. ( Autometer for best)(cheap brands like Equus won't work long.)

Will Reeve · Post by **Will Reeve** » Tue Aug 03, 2010 3:19 pm

electric sender / gauge or old style capillary? Stupid question but is there a standard thread size for these?

Will Reeve · Post by **Will Reeve** » Tue Aug 03, 2010 3:23 pm

question...does oil pressure rise linearly with engine rpm? I can't see why the valve would stick then un-stick? If stuck open you would think higher rpm would just increase pressure and help? The flicker was just that, on then off....I need that analogue gauge!

kiwicar · Post by **kiwicar** » Tue Aug 03, 2010 3:52 pm

Oil pump output pressure is is dependent on four things
1 speed of pump rotation
2 amount of oil able to "leak" past the case and impellers
3 oil pressure relief valve.
4 condition of bearings and tappet bores (ie how quickly oil can return to the sump)
The net result is that a reasonable condition pump in a reasonable condition engine will have oil pressure that rises at a low rate from idle until the flow rate through the earings and tappets maxes out, it then rises rapidly with revs until the bypass valve opens when it levels off staying at a pretty well fixed level until max rpm. The bypass valve has potential flow far greater than that through the bearings and tappets so the net result is that it infact is allways tending to close where momenterily the pressure will rise again forcing it open again. Therefor if it is sticking a little or just slow to close pressure will drop rapidly from the pump until the valve unsticks and it can close and the pressure rebuilds. Leak back through the pump internals has two effects, firstly it reduces pressure, and maor importantly rate of increase of pressure at low revs increasing the rate of rise of pressure with revs, but overall reducing pressure. Secondly it will also give rise to a rapid increase in rate of pressure rise where the back flow through the pump becomes limmiting (like through the bearings) this can give rise to the pressure and flow becoming unstable as the relief valve is rapidly shot off the seat, only to see a rapid drop of output from the pump as the flow back through the pump sudenly increases in responce to the drop in pressure.
These can easily result over time to the relief valve sticking as the type of valve is a very simple spring and piston in a cylinder with a bypass hole in the wall.
Best regards
Mike

Darkspeed · Post by **Darkspeed** » Tue Aug 03, 2010 4:21 pm

Just a note that over filling is just as bad as underfilling.

If the oil level is too high then the crank can whip the oil like a very effective whisk putting a large amount of air into the oil - the viscocity of the oil is then considerably reduced if there are patches of this airated oil within the main oil bulk it can cause pump cavitation as it goes through the pump - the air expands under the vacuum in the pump suction line losing pressure.

Could also be a resonance issue that is opening up a fracture or a loose joint in the oil pump pick up line allowing air in for a second.

A faultly pressure switch resonance effect

Loads of options

Andrew