Oil Weight Recommendations

[AZmike]

My 1989 Accord service manual recommends 5W30 for all temperatures with 10W30 shown as acceptable for warmer climates. I just got the serivce manual for my 86 Prelude (same as 86-87 Accord FI engine) and it recommends everything from 5W30 (cold climates only) all the way up to 20W50 for hot climates. I thought that everything except the compression ratio (pistons) and cam profile was the same for all A20 engines. Can anyone explain why the recommended oil viscosity changed over the years for practically the same engine? Is the heavier oil recommended for the Prelude because it's a sports car and Honda expected the engine to be pushed harder?

[DeathRat]

That might be a reason, but doubtful. I'm thinking the lower end bearing tolerances are different? If this is the case, then the Oil Weight would be different to make sure that the Oil Pump delivers right amount of oil & at the right pressure to the entire engine.

[shepherd79]

older engines required heavy oil. new engines need light oil such as 5w-30 or even 0w-30
i would recomend 10w-30/40 or 15w-30. The reason is because our engines have a lot of miles and it is better to keep them alive with thicker oil.

[AZmike]

Originally posted by shepherd79
older engines required heavy oil. new engines need light oil

In general yes. My question was why are the recommendations so different for A20As in two different cars.

[shepherd79]

it is two diff years. every year car maker reviews the owner's manuals and they makes changes.

[AZmike]

Originally posted by AZmike
My question was why are the recommendations so different for A20As in two different cars.

shepherd79, while all the things that you've said are true, none of them address my question. It's ok to admit that you don't know something. I didn't know the answer so I posted a question. I'm just trying to keep this thread on-topic.

DeathRat may be on the right track--hopefully someone else can provide some more information.

[DBMaster]

I don't know about why tje recommendations are different. (There, I will admit it) I will say that I have been using 10W-30 for years and one time accidentally put in 5W-30. I did not burn any oil or notice any difference. My trusted Honda mechanic says we should all use 5W-30 for the fuel economy benefits. It offers similar protection to 10W-30 as mutilgrade oils that end in 30 are all much the same viscosity when warm.

I would say that you should experiment and use the lightest grade oil that does not cause oil consumption. I actually used 20W-50 in my car's earlier days because I got a bunch of synthetic Amoco oil on clearance at Target back in 1992. I switched back to 10W-30 with no problems.

I still always recommend using synthetic, a decent filter (opinions abound on that topic), and changing the oil no more often that 10,000 miles (synthetic) and 6,000 (conventional).

That's it.

[DeathRat]

I based my info on GM engines, as I work with them everyday (GM Partsman). I've seen GM use 2 different weights of oil for seemingly identical engines. The differences were all internal based, mostly with the Connecting Rod Bearing tolerances, as GM used different Conn Rods & Crankshafts for different Models of Cars with the same engine. Also, in general, some engine manufacturers will change the bearing tolerances from year to year too. This sometimes causes them to change the Oil weight as well to meet demands of the changed engine. Now, I do admit I'm a "Noob" when it comes to the A20A1 engine, but I'm learning fast based upon my mechanical background.:smokin: