Get a new battery too. Cranking speed means alot in getting these started in cold weather, that's why many of us use syn oils to help it turn over faster in the cold. It may seem like it's cranking fast enough but that little improvement you get with a new battery will make a big difference. Gassers only need a couple of cylinders to fire in order to get the rest rolling. Diesels need a bit more help since the cold cylinder walls drastically cut the burn at startup. A good battery also makes it easier to cycle the glow plugs twice when it is really cold.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold