i recently changed my oil to castrol 20-50 from SAE 30 (previous owner had used this weight for 20+ years). the reason was due to excessive oil use in my car (about a quart every fill up). i was noticing a lot of blow by so i installed a new gasket on the oil filler cap, made sure the return line was hooked up under the air filter, and purchased an upgraded breather tube (flat design).

after fully draining the oil and adding 8 quarts new, the level was a little high. drove the car and now the transmission is acting weird. the car doesn't accelerate through all the gears, even revs really high without catching if i punch it. sometimes it hesitates and lurches forward as if it's not getting fuel.

this led me to check all my vacuum lines, around the oil filter housing and elsewhere. door locks and shutoff are all functional and i have good vacuum to the valves.

now i've noticed that when the car is warm everything is ok, yet in some driving situations (e.g. take off), it is still bad.

can't figure it out: if i leave the car in second gear it still has the same symptoms as described above even when cold which tells me it may be engine and not tranny.

i welcome any feedback or questions any one may have.

thanks, ben

'82 300D 193k

possibly the engine needs to get
'used to' the new weight after running so long with 30w. give it a couple days and take it up on the highway for a long run then see how it acts. keep an eye on the oil level. if you got all the old oil out and changed the filter then 8 qts should not = an overfill. tranny shifting situation should have nothing to do with engine oil.

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

i've now noticed that the engine is fine after it gets warm (ie about 20 minutes). i live in socal so the new 20-50 is probably a little thick until it gets hot?

i'm going to do a much-needed valve adjustment this weekend to see if that improves anything.

i'll keep my eye on it.

A lot of people seem to use Castrol 20w-50, is it diesel rated? Try a nice 15w-40 diesel oil, say Delo, Delvac, Pennsoil, Shell, etc..

I belive CH-4 or CF-4 is a diesel oil.

But your problem sounds like a vacum leak, I'd start pulling vacum on lines and testing them. I'm not familer with your car so hopefully someone with more knowledge can help.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200