Hello all, just bought a 79 450SL..Oil pressure is fine when car is cold and on high idle but once it warms up and the idle slows down the oil pressure drops to below 15psi accompanied by engine ticking..I am gonna change the oil first to a thicker oil because when I take out the dipstick the oil drips off like its water..gonna try some 20W-50..incase that dont work, how hard is the oil pump to change on this motor 4.5 liter? Thanks for any help or advice..

pull the trans off, then pull the engine, OR hang the motor from the inner fender and drop the subframe.

first thing i'd do is put a oil pressure test gauge on it and make sure it needs a pump. been doing this for about 25 years and NEVER replaced an oil pump on a benz. a few Volvos, yes. never saw low pressure, either. you may be correct. good luck, chuck.

I put a mix of 20w-50 and 15w-40 and it seems ok now I think..At idle in gear its 15psi..could be a little higher but I think its because of the fact that the car is idling at like 500 rpms. When I get it up to like 1500rpm the gauge is pegged. I guess only time will tell..