As far as I know James, it has always used 5W-30. As for causing damage through using 10W-40, I'm happy to rule that one out
We all hear about how modern motors have much tighter clearances than vehicles of yesteryear, so I figured "let's find out for sure". As I also own a 40 year old Leyland P76 (laugh if you will, doesn't phase me
) I compared their tolerances with each other before trying 10W-40, and the results may suprise some, as it did me. Now, as you see these comparisons below, keep in mind that the P76's recommended mineral oil grade is 20W-50. All mearurements are imperial;
PISTON CLEARANCE:
5.7L HEMI - 0.0008 - 0.0019
P76 4.4L - 0.0008 - 0.0012
PISTON GUDGEON CLEARANCE:
5.7L HEMI - 0.00035 - 0.0007
P76 4.4L - 0.0003 - 0.0006
CONROD SIDE CLEARANCE:
5.7L HEMI - 0.003 - 0.0137
P76 4.4L - 0.010
MAIN BEARING CLEARANCE:
5.7L HEMI - 0.0009 - 0.002
P76 4.4L - 0.0009 - 0.0025
BIGEND BEARING CLEARANCE:
5.7L HEMI - 0.0007 - 0.0023
P76 4.4L - 0.0006 - 0.0022
CAMSHAFT JOURNAL CLEARANCE (LOWEST TO HIGHEST):
5.7L HEMI - 0.0015 - 0.0035
P76 4.4L - 0.0005 - 0 0035
HYDRAULIC TAPPET CLEARANCE:
5.7L HEMI - 0.0007 - 0.0024
P76 4.4L - 0.0008 - 0.0023
INLET VALVE STEM TO GUIDE CLEARANCE:
5.7L HEMI - 0.0008 - 0.0025
P76 4.4L - 0.001 - 0.003
EXHAUST VALVE STEM TO GUIDE CLEARANCE:
5.7L HEMI - 0.0009 - 0.0025
P76 4.4L - 0.0025 - 0.0035
TOP RING GAP:
5.7L HEMI - 0.0090 - 0.0149
P76 4.4L - 0.010 - 0.019
SECOND RING GAP:
5.7L HEMI - 0.0137 - 0.0236
P76 4.4L - 0.010 - 0.019
TOP RING SIDE CLEARANCE:
5.7L HEMI - 0.0007 - 0.0026
P76 4.4L - 0.002
SECOND RING SIDE CLEARANCE:
5.7L HEMI - 0.0007 - 0.0022
P76 4.4L - 0.002
Bit long winded, but I thought some of you would find that interesting.
I'm not sure that I want to drop to 0W-20 though James. After the basic comparison above, I'm still struggling with the idea of going any thinner than 5W-30, though I might try 5W-20 on the next service...