Oil pressure maladies

[StephenRae]

I have just fitted a data logger to my FF1600 and am surprised by how much the oil pressure varies during the course of a lap. I had expected a drop off of pressure as the oil heated up but the variations don't seem to be directly linked to revs. Is this normal?

[thebear]

Possibly due to inertia moving the oil away from the pickup during cornering, braking and accellerating.

Do you have baffles in you sump?

Of couse if it is a dry sump system the problem lies elswhere.

[Tim Falce]

What variations are you getting and under what circumstances, I.E. Acceleration, cornering or braking and hot or cold?

[StephenRae]

Thanks "thebear", it is dry sumped but I still think it may be worth having a look at the pickup to see if there is an obstruction.

Originally Posted by falcemob

What variations are you getting and under what circumstances, I.E. Acceleration, cornering or braking and hot or cold?

As I said the variations don't seem to match the revs, or the position on the track for that matter. For example on the two straights at Anglesey it gets up to about 6700 and shows a different pressure every time. I'll have another look at the data and report back!

[thebear]

Originally Posted by StephenRae

As I said the variations don't seem to match the revs, or the position on the track for that matter. For example on the two straights at Anglesey it gets up to about 6700 and shows a different pressure every time. I'll have another look at the data and report back!

To rephrase the problem:

At max revs different oil pressures are recorded.

Does the OP fluctuate at peak or are the readings stable just varying in max indication?

[StephenRae]

Originally Posted by thebear

To rephrase the problem:

At max revs different oil pressures are recorded.

Does the OP fluctuate at peak or are the readings stable just varying in max indication?

OP fluctuates throughout the range, as the oil heats up the general trend is downward. A manual gauge on the same engine shows a general deterioration down to about 18lbs 'inch at 1500revs, but is not sensitive enough to show the variations. I wonder if with the logger sampling so often per second there is some sort of electrical bounce going on!

[ian.stewart]

May be a silly question, are all the connections on the data logger and pressure sender clean and tight??
Ian

[StephenRae]

Originally Posted by ian.stewart

May be a silly question, are all the connections on the data logger and pressure sender clean and tight??
Ian

They seem to be OK.

The data from two consequetive laps with exactly the same lap times shows variations of from -19psi to +24psi at the same place on the circuit and virtually the same revs.
From bitter experience, when the oil return union from the pump broke off a while ago, it took half a lap to use all of the oil in the tank, so the data represents at least one complete 'recycle'.
The lowest reading was 21.5psi which I can live with but it is annoying not to know if these fluctuations are normal or a warning of impending doom.

[phoenix]

It sounds extremely worrying. With a dry sump system you should expect a constant pressure, only dropping at lower revs when the oil is hot. There should be no pickup problems at all as you have a large resevoir of oil in a tall, narrow tank so the output to the pressure pump should always be submersed. If the system has worked perfectly well for a while previously, then the design of the system would seem to be ok and I would suspect one or two other things.

Have you tried swapping the pressure sensor? That would be the first thing I would do. Different types (makes) seem to go wrong in different ways. When they go faulty, some read high, some read low, some don't read at all and some give a variable output. This would cause the effect you are seeing. I would also expect a mechanical gauge to respond very quickly to changes. As you haven't seen such variations on the gauge then I would suspect the elecrical pressure sensor.

I would also check the filters, which should be fitted over the scavenge pipes in the sump. Any blockage there could result in insufficient oil flow from the sump to the oil tank. I doubt this is the cause of the variation on the pressure side, however, as you would be likely to have a seized engine, no oil in the dry sump tank and a block full of oil by now!

[StephenRae]

Thanks Phoenix...I agree it could be a sender problem, I should have mounted it remotely on some aeroquip and I'll talk to Dataspares who have been very good even though I didn't buy the kit from them.

[greenamex2]

Do you log oil temperature as well as pressure?

Can you post a screenshot of a couple of comparison laps?

I have years of datalogging at most circuits and haven't seen the situation you describe under normal conditions.

[StephenRae]

Originally Posted by Denis Bassom

Do you log oil temperature as well as pressure?

Can you post a screenshot of a couple of comparison laps?

I have years of datalogging at most circuits and haven't seen the situation you describe under normal conditions.

Thanks Denis...I'll do my best to extract it from my ancient laptop this evening.

[ian_w]

Sounds more like a measurement problem to me if there is no fixed trend over a lap.

Just because you have a dry sump doesn't mean you can't get oil starvation. The oil in the dry sump tank will still slosh around and can uncover the oil pickup with the obvious results. Have you tried running a higher level in the oil tank.

The other possibility is oil aeration. The 'oil' being scavenged out of the engine will contain a high proportion of air. The dry sump tank will typically be designed with some sort of swirl pot arrangement at the top for the oil return line. If this is not a very good design it is possible that all the air has not separated out before the oil is drawn back into the engine from the bottom of the tank. This aerated oil is bad for the crank bearings and if present in large enough quantities could give you the oil pressure symptoms you are seeing.

[StephenRae]

Originally Posted by ian_w

Sounds more like a measurement problem to me if there is no fixed trend over a lap.

Just because you have a dry sump doesn't mean you can't get oil starvation. The oil in the dry sump tank will still slosh around and can uncover the oil pickup with the obvious results. Have you tried running a higher level in the oil tank.

The other possibility is oil aeration. The 'oil' being scavenged out of the engine will contain a high proportion of air. The dry sump tank will typically be designed with some sort of swirl pot arrangement at the top for the oil return line. If this is not a very good design it is possible that all the air has not separated out before the oil is drawn back into the engine from the bottom of the tank. This aerated oil is bad for the crank bearings and if present in large enough quantities could give you the oil pressure symptoms you are seeing.

You have a valid point. The oil system is standard Reynard with 3 port combined filter/pump. The capacity is only 1 gallon and I have deduced that it is completely recirculated every 30 seconds or so.
The traditional gauges I have used in the past have all shown the general trend downwards as the oil has heated up but maybe the logger is sensitive enough to react when an air bubble 'cushions' the pressure on the sensor?
I hope the problem turns out to be electrical, if you have hit the nail on the head then virtually every FF1600 is running on the edge of disaster as they all have similar systems.

[norman-normal]

One of the great virtues of synthetic oil is less foam. What are you using?

[StephenRae]

Originally Posted by norman-normal

One of the great virtues of synthetic oil is less foam. What are you using?

My engine builder prefers 20/50 on the basis that that was what the engine was designed for. I have used synthetic in the past in various engines and have always been impressed by the abuse it will take...I'll try it next time out as I have no time to do anything else and it will be a true comparison.

[norman-normal]

The engine wasn't designed 20/50. 20/50 was designed avarage motoring conditions. Synthetic will be a prudent investment.

[JamesH]

Originally Posted by StephenRae

My engine builder prefers 20/50 on the basis that that was what the engine was designed for. I have used synthetic in the past in various engines and have always been impressed by the abuse it will take...I'll try it next time out as I have no time to do anything else and it will be a true comparison.

I have found (in 4 stroke kart engines) that moving from synthetic back to 'normal' can lean to glazed bores if engine is not thoroughly cleared out of old oil - glazing leads to lack of compression So take care when moving from one to the other.

James

[norman-normal]

Glazed bores would have to be IMHO, a product of worn rings, too much clearance and over heating; witch would agree with statements of major oil producers.
Could it be James, that you took the engine apart after you experienced problems? over heating perhaps?

[JamesH]

Originally Posted by norman-normal

Glazed bores would have to be IMHO, a product of worn rings, too much clearance and over heating; witch would agree with statements of major oil producers.
Could it be James, that you took the engine apart after you experienced problems? over heating perhaps?

No, def. glazed after oil change. You could see the glazing. I simply honed the bore and everything was OK afterwards, compression back to normal. Saw it on other karts engines also - someone moved from Synthtic back to 'normal' and immediately started to gets puffs of smoke on cornering because of a lack of sealing due to glaze. Honed the bores and all OK again.

These are only aircooled Honda GX160 engines from Prokarts, so not exactly high performance. (5.5 Hp!)

James