I have put in some hours looking through the various oil and oil filter threads, and my key takeaway is that the 1998 4.0 wants the Napa Gold 1515 and oil w/ zinc so you have Rotella (low zinc), Valvoline VR1 (dino) /Kendall GT1 (semi synth) high zinc options. I do not want more oil leaks so I think avoiding changing to synthetic would be wise (?) but I am concerned about what weight oil to use for the cold winter? Semi-synthetic? I have a plug-in oil pan heater installed for when I am parked at home in the winter to aid with cold start oil viscosity but that won't help me if I am parked somewhere outside away from an outlet and it is 0 degrees out.

Stock specs call for 10w40:
Valvoline VR1 comes in a 10w30 and a 20w50.
Rotella of course is 10w30 & 15w40.
Kendall GT1 comes in a 5w30, 10w30, 10w40.

So I suppose the essence of my question is is 10w30 OK in the winter or is that lower weight at the upper end going to lead to damage somehow? Was hoping someone with more knowledge of what temperature band that extra 10 of weight might matter in and if I am likely to encounter that if I swap the oil weight in the spring for something like 15w40 or 20w50?

 

10-30 is good for the winter and 15-40 for the summer

 

The manual says 5w30 when it’s cold outside and 10w30 in the summer. Everyone else around here seems to agree you need thicker, like 10w40.

I’m been running 0’Reilly’s 5w40 for this summer and when it I feel that chilly Indiana winds I’m switching to Amsoil 5w30 and I’ll see how it goes.