C-5 Oil Change Requires "Special Procedure"

By Al Engel

The owner’s manual cautions the C-5 owner that an oil change requires a "special procedure, consult the Shop Manual ($120 US Dollars), or see Mr. Goodwrench for his services" (not an exact quote, please permit me to paraphrase). A few years back, when I was doing the "college thing", I worked part-time for my friendly local Chevrolet Dealer. As a part-time, rookie mechanic, you get to do the oil changes, chassis lubes, bulb changes, etc. At that time, oil changes on 1968 Chevy’s, with the "Blue Flame Six" and "Powerglide" tranny, were a little less complex then what is required for our C-5s. I’m telling you this to make the point that the "Master Mechanic" (Father Goodwrench) is not usually assigned to perform the oil changes by the Service Manager… the most junior, lowest hourly cost employee gets the honors of the oil change job. This is also the person who does not get very much training. After all, how difficult can it be to change the oil and filter? Just do it, and move on to the next oil change!

Well, while the process is not intricate, there are some unique procedural requirements that are dictated by the design of the car. I am skeptical that the junior Mr. Goodwrench (let’s just call him "Wrench") will be aware of, and employ the "special procedures" required of a proper oil change on the C-5.

Just a note to illustrate by paranoia over "professional" oil changes…. This past winter, while on a road trip for business in rural Pennsylvania with my Aurora, the "Change Oil Soon" message appeared on the digital display. I soon drove past an Oldsmobile Dealer. The Quick-Lube sign guaranteed "an oil change & filter in 29 minutes for $29.95". I was about an hour ahead of schedule, and it was about 12 degrees outside, so I pulled in. The Service Manager was very friendly, said "no problem, we’ll have you out-a-here in 29 minutes". The Service Manager assigned "Wrench" to the task.. I sat down, had a cup of coffee, and 29 minutes and $29.95 later, I was on my way…. I thought. I got back into the Aurora, started it up, the same display that warned me I needed an oil change, now told me "Oil Level Low". But "Wrench" had just performed a "professional" oil change! It seems "Wrench" did not realize the Northstar engine in the Aurora takes EIGHT quarts of the slippery stuff…. not the standard four, five with a filter. Many apologies later, I was on my way. This was an Oldsmobile Dealer, and the guy doing the oil change didn’t know my Oldsmobile Aurora required 8 quarts! I’ll change my own oil, regardless of the temperature outside in the future, thank you.

What Makes an Oil Change on a C-5 Special? The oil pan on the C-5 is a large, aluminum casting, with a pair of side wings. The oil pan holds 6 quarts (6 ½ with filter). The "old" way to make a high capacity oil pan was to weld a deeper sump onto the bottom of the pan. Take this route on a C-5, and the oil pan would be scraping on the road! Also, the engineers at Chevrolet went to great pains to deliver a car that has a very low coefficient of drag (CD). Among the tricks to achieve that low CD is a low body height, and a flat bottom. In fact, working under my C-5, I was amazed how flat the boys (and women) of Bowling Green were able to make the bottom of the Corvette. Knock the wheels off a C-5 and you would have a very effective toboggan. That flat bottom includes a flat oil pan. A very big, flat oil pan with no deep sump hanging down.

So what does this have to do with an oil change??? This is an article about how to change the oil! Remember that flat, high capacity oil pan necessitated by the quest for low CD? How do you get all the old, grungy oil out of a large, flat pan? You tilt it! Yep, that’s the "special procedure", you tilt the oil pan forward so the oil can run out of the hole in the front of that large, flat pan. An elevation of only 4 to 6 inches on the rear end of the car will do the trick. Don’t believe this isn’t necessary. I’ll bet another 1 to 1 ½ quarts of oil came out of my C-5 after the draining had stopped when I raised the rear of the Vette. Actually, the "Official Tech Manual" specifies the bottom of the oil pan is to be "absolutely flat". This "flat" attitude may be very difficult for the backyard mechanic to achieve, as explained in the following paragraph. My experience has shown the slight rear elevation gets more oil out of the pan then the "absolute" level approach. The book says to allow a minimum of 7 minutes to the oil to drain.

This unique tilting requirement may be further exasperated by the procedure most backyard mechanics will use in doing and oil change on their C-5. The car is low, real low. To get my floor jack under the car, I need to first drive the front wheels onto some boards to elevate the front of the car an additional 2 ¼ inches so my floor jack can get under something solid. For an oil change, I place the floor jack to catch the front cross brace from the front end of the car. I then place jack stands under the front frame hold-down holes, and use hockey pucks between the saddle of the floor stands and the frame, so as not to crush the fiberglass that wraps down and under the frame rails. After raising the car, you can then get under and remove the oil pan plug. The car, however is now "nose high". Even after lowering it, the wheels are still on top of the boards, giving the car a tilt to the rear, emphasizing the oil entrapment problem of the large, flat pan with its drain hole in the front. You must raise the back of the car! Even when using a four point hoist (as Mr. Goodwrench, or his associate "Wrench", will) the car is at best "level". Raising the rear 4 – 6 inches is still required. Note: Before, I begin this procedure, I get the oil temperature up to about 140F degrees…. warm enough for the oil to flow easily, not so hot as to cause burns on my hands. The digital display panel on the dashboard of the C-5 will report the oil temperature with the proper sequence of button pushing.

Now it’s time to again raise the front end, replace the drain plug, and focus attention on the oil filter. Remember that oil pan you are torqueing the drain plug into is aluminum, not steel. Be careful not to cross-thread the plug, and do not over tighten (26 foot pounds)! You don’t want to even think how much your Chevy Parts Guy will charge you for a replacement of the oil pan on an LS-1 motor.

The Oil Filter Change is more traditional. The AC PF-44 filter in one of GM’s smaller filters. Located at the left rear corner (the small block heritage lives on) of the engine. It is nestled in a cavity formed by the oil pan and the frame rail. The bottom of the filter is flush with the bottom of the pan. An "end cap filter wrench" works best. "Strap wrenches" with attached handles will not fit in the tight quarters allowed. After removing the old filter, check to make sure the oil filter gasket came out with the old filter. A common problem that promotes oil leaks is the old gasket sticking to the mounting flange, and a new filter and gasket being installed on top of the old gasket. Before I put the new filter on, I fill it with fresh oil. Just one of my mental hang-ups. Pre-filling the filter gets the new oil circulating after start up as fast as possible. Something you must do, is lubricate the new gasket with some motor oil before screwing the new filter into place.

Lower the car, and add 6 quarts of Mobil 1 synthetic 5-30. (10-30 is a good substitute, and for + zero temperatures, GM says it’s OK. 10-30 has less viscosity modifiers in the formula then 5-30 and will do a better job of lubricating that LS-1 powerhouse). A minimum of 3 minutes is called for to allow the oil to drain down from the rocker cover where you just pored the oil into the engine, down through the drain holes inside the engine, and into the oil pan. Fire up the engine, watch for the oil pressure to register north of 40 lbs. at 2000 RPM, and check for leaks.

Now it’s time to get out of the grub-duds, shower, and go for a drive. The time the car sat while you got cleaned up, provided ample time for the oil to drain down into the pan. Before you go for that drive, check the oil level with the dipstick and add oil, if so indicate, to the "full" mark. Do not over fill the crankcase! Cycle your Digital Information Center display to "Remaining Oil Life", and hold the "Reset" button for five seconds. "99% oil life remaining" will be displayed. The oil life indicator gizmo monitors many operating parameters in determining the remaining useful life of the engine oil. It will count the number of starts, number of crankshaft revolutions, maximum engine temperature, did the oil reach a high enough temperature to boil off any condensation in the crankcase, etc. This provides a much better prediction of when to change oil then just miles traveled. My experiences with my 92 LT-1 and two Auroras indicate I get about 4,500 to 6,000 miles before I get down to 30% remaining life, the point at which I generally change the oil. [Except for that time I reference above when I allowed the Aurora to go down to the "Change Oil Soon" warning that is displayed when less then 10% oil life is remaining.] I do an initial oil & filter change at 1,000 miles on new cars, regardless of what the Remaining Life percentage indicates.

One last word of advice….. you put 6 ½ quarts into the engine for this procedure. That means up to 6 ½ quarts will be drained out. Make sure the drain pan you are using will accommodate the larger quantity of oil…. C-4s, and most C-3, 2 and 1’s held only 4 to 5 quarts. Dispose of your used oil and filter in an environmentally friendly manner.

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