flyboy
12-08-2012, 08:49 AM
Hi there.
After reading few numerous threads, including those on the third gen forum, I thought I'd offer my thoughts on pre-filling the oil filter. I'm sure Mal or some others might offer their professional opinion.
Just my honest opinion on the subject, hope not to offend anyone :io:
From the third gen forum:
Pre-filling the oil filter simply saves the engine running dry for the second it takes for the pump to fill the filter, although I'm not convinced it really is necessary. I suppose it's like filling the oil pump with vaseline or thin grease after overhaul so that it is "primed". I've known blokes to remove the oil pressure switch and apply compressed air to the oil lines to purge all the old oil out, then after refilling with oil, crank the engine over with coil disconnected till the oil light goes out.....bit anal but to each his own.
This is complete bollocks.
Firstly, let's look at what happens when you drain the oil.
Even if the oil is really hot, you are still only draining the contents of the filter and sump. The top of the engine and metals parts with close contact retain an oil film. If you want a good demo of this, drop the hot oil and filter out of your car and leave it to drain for an hour, then stick your finger inside the oil filler cap and run your finger over the valve train. Is it dry? No.
Secondly, let's look at cold engine starts.
When people say the majority of engine wear occurs at startup, they are right. But it's not because of the split second without oil pressure. It's mainly because of acids which form from combustion products and moisture. Modern engines are designed to run hotter for better efficiency. This means that by idling a cold engine, it takes much longer to warm up and will increase emissions.
If nice, warm, high pressure oil was such a necessity to avoid cold start engine wear, manufacturers wouldn't recommend driving the car almost immediately after the key is turned.
Thirdly, let's look at oil pressure.
I did an oil change on the 380 last week. I (shock/horror) installed a dry oil filter and didn't turn the engine over with the plugs out to develop oil pressure. On start, the oil light disappeared in less than a second, which is perhaps half a second longer than normal. In that half a second at idle (say 1000rpm), the crank turns less than 10 times. That's right, ten revolutions of the crank with a slight residual oil film before pressure is developed is going to do sweet FA damage to your engine.
When you oil a door hinge and leave it for 2 weeks, then open the door, is it dry and creaky again? No. While I will get the inevitable (you should look after your car engine more better than a door hinge type comments), the situation in a car is exactly the same. An oil film will remain and protect your engine for that split second before oil pressure is developed.
So, while you might think you are doing the right thing by your engine, the physics are that pre-filling your oil filter does nothing in the big scheme of things and you are simply wasting your time IMHO. If you really want to look after your engine, you'd be better off spending your time washing the dirt and grit out of your oil funnel that has been gathering dust in your garage before you use it every time.
As a last point, the turbine (jet) engines on the aircraft at my work take about 60 seconds to cold start, and for the first 45 seconds develop almost nil oil pressure. Yet they do 10 or 15 starts a day, 12-15 hours per day, and do tens of thousands of hours between overhaul. Trust me... half a second without oil pressure once every 5000k is absolutely nothing to worry about.
After reading few numerous threads, including those on the third gen forum, I thought I'd offer my thoughts on pre-filling the oil filter. I'm sure Mal or some others might offer their professional opinion.
Just my honest opinion on the subject, hope not to offend anyone :io:
From the third gen forum:
Pre-filling the oil filter simply saves the engine running dry for the second it takes for the pump to fill the filter, although I'm not convinced it really is necessary. I suppose it's like filling the oil pump with vaseline or thin grease after overhaul so that it is "primed". I've known blokes to remove the oil pressure switch and apply compressed air to the oil lines to purge all the old oil out, then after refilling with oil, crank the engine over with coil disconnected till the oil light goes out.....bit anal but to each his own.
This is complete bollocks.
Firstly, let's look at what happens when you drain the oil.
Even if the oil is really hot, you are still only draining the contents of the filter and sump. The top of the engine and metals parts with close contact retain an oil film. If you want a good demo of this, drop the hot oil and filter out of your car and leave it to drain for an hour, then stick your finger inside the oil filler cap and run your finger over the valve train. Is it dry? No.
Secondly, let's look at cold engine starts.
When people say the majority of engine wear occurs at startup, they are right. But it's not because of the split second without oil pressure. It's mainly because of acids which form from combustion products and moisture. Modern engines are designed to run hotter for better efficiency. This means that by idling a cold engine, it takes much longer to warm up and will increase emissions.
If nice, warm, high pressure oil was such a necessity to avoid cold start engine wear, manufacturers wouldn't recommend driving the car almost immediately after the key is turned.
Thirdly, let's look at oil pressure.
I did an oil change on the 380 last week. I (shock/horror) installed a dry oil filter and didn't turn the engine over with the plugs out to develop oil pressure. On start, the oil light disappeared in less than a second, which is perhaps half a second longer than normal. In that half a second at idle (say 1000rpm), the crank turns less than 10 times. That's right, ten revolutions of the crank with a slight residual oil film before pressure is developed is going to do sweet FA damage to your engine.
When you oil a door hinge and leave it for 2 weeks, then open the door, is it dry and creaky again? No. While I will get the inevitable (you should look after your car engine more better than a door hinge type comments), the situation in a car is exactly the same. An oil film will remain and protect your engine for that split second before oil pressure is developed.
So, while you might think you are doing the right thing by your engine, the physics are that pre-filling your oil filter does nothing in the big scheme of things and you are simply wasting your time IMHO. If you really want to look after your engine, you'd be better off spending your time washing the dirt and grit out of your oil funnel that has been gathering dust in your garage before you use it every time.
As a last point, the turbine (jet) engines on the aircraft at my work take about 60 seconds to cold start, and for the first 45 seconds develop almost nil oil pressure. Yet they do 10 or 15 starts a day, 12-15 hours per day, and do tens of thousands of hours between overhaul. Trust me... half a second without oil pressure once every 5000k is absolutely nothing to worry about.