I believe mine called for 10W-30 but I only use 10W-40 year round. Temperatures can get down to -30F which would make for hard starting for the van and for me. The lowest it has gotten the last few years is around -10F and it still cranks and starts just fine. Your owner's manual will show the oil to use in different temperature ranges but you might want to go up to one weight heavier with a high-mileage engine.
I just found a '94 service manual. The chart in it lists 5W-30 for temperatures below 100F including less than -20F, and it lists 10W-30 for temperatures above 0 degrees including past 100 degrees. The "API", (American Petroleum Institute) rating at that time was already up to "SG". I don't know what the current ratings are but anything you find on the store shelves today will meet or exceed what your engine was designed for.
5W-30 stays thinner when it's cold so the engine will crank easier. Also, since it flows easier, the engine doesn't have to work so hard to push it through the passages, and there's supposed to be less friction so the fuel mileage will be better. That "less friction" is misleading. The goal of the oil is to eliminate friction so metal parts don't grind on each other. The friction they're referring to here is the force needed to get the oil to move to those places. Lighter oil moves easier so it robs less horsepower from the engine but thicker oil stays in the critical places longer and does a better job of isolating those moving parts. As you can see, it's a tradeoff. Better fuel mileage and possibly easier cranking in cold weather vs. Better protection from wear, and potentially longer engine life.
I prefer the thicker oil because of the reduced engine wear but also because I regularly drag around a tandem axle enclosed trailer that's bigger than the van. The engine already gets nice and toasty on hot summer days but with that trailer on the highway there is so much wind resistance I can't even hit 70 mph going down a long steep hill. The engine has to work really hard and at those temperatures the thicker oil will lubricate better.
There really isn't anything permanent you can do about the leaking head gasket. That's a pretty big job but it can happen on any engine and brand. In the future the best way to avoid a repeat failure is to replace the engine coolant every two years. The antifreeze is a type of alcohol and that won't change, but what changes is the additives wear out in about two years. Those are mainly water pump lubricant and corrosion inhibitors. It is normal for some combustion gases to sneak into the cooling system, then it forms acids that corrode metal parts including the edges of the head gaskets. Replacing the coolant gets those acids out and new additives in. Here again you have "do as I say, not as I do". May original radiator rusted out too badly to keep on patching holes about 12 years ago. At that time I installed a new radiator and that's the last time I flushed the cooling system and put in all new antifreeze. It's a miracle nothing has leaked so far, but that's why I love this van so much. It just refuses to break down.
Monday, April 8th, 2013 AT 11:54 PM