Have '88 420 SEL w/163K that runs exceptionally well.

For the last 3K miles, I have been running on 20W-50. Went to this based on the conventional wisdom that a high-mileage V-8 needs the heavier oil, especially in steamy South Florida.
The 20W-50 exhibited these characteristics: I perceived some increase in low-end engine power and acceleration. However, produced different engine sounds and some higher end vibration (almost imperceptible). I consumed more oil w/20W-50, but no decrease in mpg. Also, smelled more exhaust fumes w/20W-50.

Well, recently I rad a post that the 10W-30 (or lighter oil) will more quickly lubricate the top end of the engine at start-up, particularly after sitting overnight, etc.

So- I just switched back to 10W-30. Engine sound differed-and no vibration. No smells, either. And I might be imagining this, but a slight loss of low-end power compared to the heavier oil.

What do you guys think? Should I stick to the 10W-30?

Bob

10W-30 is too light for your climate unless is a a full synthetic oil. In that case it is good to about 90F ambient temp. I would immediately go back to 20W-50 from a major brand. Typically a heavier weight oil would reduce oil use and create more internal drag (less horsepower) so your discription is opposite to what it suppose to happen. Good luck.

Bob,

You can avoid most of the what weight, etc by using the closest synthetic to whatever is called for in your owner's manual. I assume for FL temps it could be anything from a 30W to 10-40 as a function of whether you change from cool time of year to hot time of year.

Personally, I would use Mobil 1 10W-30 in winter and Mobil 1 20-50 in summer - i.e. change in between. I used to live in FL and know that it can get so hot, many can't imagine using a 20-50, but I think it is logical.

Another point - since synthetic flows better in the winter than non-synthetic, I suspect 20-50 would be OK for most of the year.

Bottom line point from me that you will hear consistently is to USE SYNTHETIC LUBRICANTS - THEY ARE BETTER IN EVERY RESPECT.

George

I would run 15W-50 Mobil 1; it is not offered in a 20W-50 weight. And it'll be good for you year-round

It's Hot on The Gulf Coast Too
 

Brother of The Benz, Robert Boyer
As you can read, most of us use Mobil I, 15W50 for the higher temperatures.
Here in Houston, it satisfies the winter temperatures as well.
Many use this oil for the extended oil changes as well as it's superior lubricating properties.
For me, I do the 3500-4000 mile oil and filter change regardless of the base of the oil.
My 103983 engine with 177,000 miles has never had the engine serviced, not even valve stem seals.
Clean oil is the name of the game, not it's base.
In reply to the vibs you felt in your engine, could you have over filled the crankcase causing oil to be slung up by contact with the crankshft?
There should be no appreciable amount of engine performance change between the two oil weights.
Return to the heavier oil and keep accurate records.
Happy Trails Beep Beep from The Spiderman in Houston!!!