Dry Sump vs. Wet

I can attest to the fact that the XK with a 12 qt. sump will still pump oil with only 4 quarts left. I know all XK's leak oil but mine leaks more than most. I lose about 3 oz. per gallon of gas with average driving and slightly less on a long trip. It loses a lot out the slinger when it is shut down because the engine has about 170,000 miles on it. (There is an up side to this - with fresh oil flowing into the sump regularly, the time between changes can be extended significantly.) I understand some early motorcycles had "total loss" oil systems where an oil resevoir provided oil by gravity feed and it just dripped out on the road. Ah - the good old days. No oil filter to worry about. BTW - what does "dry sump lubrication" mean anyway? It seems almost like a contradiction. I have always been a bit puzzled when I read that term but never looked into it. Until recently, I was trusting my perceptions regarding whether I had checked the oil level rather than being systematic about it. I occasionally got about six quarts low (still on the dip stick) before I thought about checking it. This has caused a couple of amusing reactions from service station attendants, by the way. I never fill it above ten quarts as it seems to leak even faster when full. I try to keep it at the low mark. A couple of months ago, I noticed a loss of pressure when I took a left uphill curve under acceleration. One might wonder why I would be looking at the oil gauge under such circumstances and all I can say is it wasn't a conscious thing - it's just that the gauge is in my peripheral vision and there is something in my brain that triggers alarm when there is a sudden movement in that area. Anyway, I was not carrying a quart of oil in the boot and my home was about five miles away. Since I had pressure with conservative driving, I continued toward my source of Castrol 20-50 in my garage rather than turn around and go the same distance to the nearest convenience store. Unfortunately, the last half mile is up a steep private road where going up at constant speed resulted in no pressure so I had to get a running start and actually decelerate on the steepest parts. The net of this is I was down to three quarts when the pickup was out of the oil under acceleration or hard cornering. While four quarts is full for a lot of modern engines, it is marginal for the XK. Three will apparently provide oil running level at constant speed. I now add a quart every time I get gas and only occasionally don't check the level when I am in a hurry. Maybe I should always check it before I start it. I could have avoided the burn scar on my right hand that way. I now keep a pair of painters gloves in the door pocket for that task. - Bruce Cunningham

Hey, Bruce - A normal oil system is referred to as a "wet sump" system because the lower ends of the connecting rods occxassionally splash some oil up to lubricate the bottoms of the cylinders through splashing! A "dry sump" system keeps the rod ends out of the oil (power loss due to friction!) and has an external tank (and pump, perhaps) to move oil to the main oil pump and, hence, to the bearings unbder pressure. No power loss due to engine parts trying to move through oil! Shorter engine life, sure, but we're talking competition (the D-Type had a 'dry sump' oil system), and the goal is, not only to finish, but to finish first! Incidently, I'm ex-WECo (Princeton, NJ - ERC) - if there are any tech/prof openings within ATT/Lucent that you can claim a bounty for filling, let's talk! Send personal e-mail re this matter. Larry Schear, Twin Cam, Inc

Good morning Bruce, I like to jump in when I actually have technical knowledge to give, Mostly I just read. :-) Dry sump...somewhat of an oxymoron but understandable. With a dry sump system the oil pan is usually an abbreviated catch basin that allows the engine to be mounted much lower than usual. Formula and sports racing cars (Is my age showing here?) :-) almost always use this type of system to lower the center of gravity of the car. It also allows better control of the oil and facilitates easy insertion of an oil cooler and filtration system. OK back to the pan... It will usually be a near half cylinder that is very close to the crank/rod rotating assembly, and have a catch channel, running the length of the engine, in the bottom center of the "oil pan". The pump will usually be an external belt driven affair with at least two stages. The first stage is known as the scavenge pump or stage. This is hooked to one or more fittings in the catch channel that sucks the oil out of the "pan" and pumps it into a holding tank. En route to the tank there may be oil filters and coolers as needed. The tank is then the feed source for the pressure stage of the oil pump. A hose directs cooled, filtered, and degassed (As in most of the entrapped air has had a chance to escape.) oil to the pressure stage where it gets pumped into the engine. Is it "dry"? Well no not in a dry dusty desert kinda way, but the volume of oil in the pan is substantially less that with a traditional wet sump system. 911 Porches use such a system as they too have 12 quart capacity and use the oil as a cooling medium for the engine. I suspect there are other production cars that use such a complex and costly system but not many. - Cheers, Ken Boetzer

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