SAE 30 or 15w40?

[h2odrx]

which would you use for summer driving? and why? what are the bennys?

 

[tonkadoctor]

15w-40 in the IDI and 5w-40 synthetic in the PSD.

I don't like straight weight oils and don't beleive in changing weight from summer to winter.

Simplest I can explain it is that Multi weight oils provide the cold flow characteristics and ease of starting of a lighter weight oil with the protection of a higher weight oil at high temperatures.

Something as little as switching from 15w-40 Dino to 5w-40 Syn made a huge difference in how the PSD starts cold and the only reason I ain't switching the IDI to it is that I am selling it but I would bet that there would be a noticable improvement in it too.

 

[rubberfish]

15w40 all year round for me.
Because that's how I was brought up.
No other reason for it.

 

[Mr_Roboto]

I tried 30w oil because the oldtimers stated that for diesels straight weight was better because the multigrades broke down more quickly (probably true in the old days).

Well I didn't like what the 30w did to my oil pressure (too high when cold and too low when hot) and I drained it way before my regular interval.

15w40 for me and no going back.

 

[stiesel]

15w-40 in the summer. 5w-30 synthetic in the winter.

 

[sle2115]

15W40

15 Weight cold
40 Weight hot

Easier starting cold, higher oil pressure hot. The IDI's aren't known for high oil pressure anyway, so I like to do what I can to raise it.

 

[h2odrx]

15W40

15 Weight cold
40 Weight hot

Easier starting cold, higher oil pressure hot. The IDI's aren't known for high oil pressure anyway, so I like to do what I can to raise it.

I see 60 psi at highway speeds

 

[sle2115]

I see 60 psi at highway speeds

So do I. Is that with 15w40 or 30 weight? My small blocks generally see 80 or so at the same speed...and maintain 40+ at hot idle - not something most IDI's do.

 

[dakotajeep]

15W40.....I am a total newb!!!! It just seems to make sense...

 

[h2odrx]

So do I. Is that with 15w40 or 30 weight? My small blocks generally see 80 or so at the same speed...and maintain 40+ at hot idle - not something most IDI's do.

15w40 is all I've been using and now i've added it to my 3.2 that has 180k miles. So with My 87 I see 20psi at idle hot and 60psi at 2200rpms.