15W-40 synthetic instead of 5W-30 on a Honda engine?

Can I use 15W-40 synthetic oil motor oil instead of 5W-30 (oem specified) - the car is 16yrd old with 100k mileage?

I have some left over 15W-40 synthetic oil motor oil.

Also what is the shelf life of these oil unused?

I wouldn’t.

If you’re in El Paso or Dubai 15-40 is fine


As for shelf life as long as there is no settling/seperation of components the oil remains good.

You can use 5w30 synthetic, but 15w40 is a diesel oil that has additives that can hurt your catalytic converter. Save it for your lawn mower.

How much do you have? If you really want to use it, change oil with the recommended 5W30 and top off with the 15W40. That way you won’t have too much 15W40 in the crankcase at any given time. Unless you add a quart every month. The problem is that the lower viscosity 5 weight is for start-up and the 30 weight is for normal running conditions. You are asking if you can use a significantly more viscous oil for start-up and for a warmed up engine. To me, large quantities of 15W40 is asking for trouble, no matter how old the car is. Of course, if you want to accelerate engine damage so that you can get a new car, using 15W40 would be heading in the right direction.

Nope. Don’t do it. Bad for your engine, bad for your catalyst.

Nothing to gain by using it. Oil is cheap, use the right one.

I am in Northern California - I never needs to add oil after an oil change - it doesn’t burn oil.

Then don’t do it. Give it to a farmer, use it in your lawnmower. Don’t put it in the Honda.

Nope,use it in your lawnmower or give it to a Diesel owner as the others said,the high metal content and higher viscosity can cause problems,these different grades are produced for a reason.

Nope I wouldn’t either. Unless you have gallons on hand, what can it be worth? Give it to a garage or take it to the recycling center and someone else can put it in their Honda.

In that case stick with the OEM oil. And when an engine has accumulated 100,000 miles and runs good and never needs oil added between changes I suggest that the owner continue with their obviously good maintenance habits.

Thanks all - will do.

You don’t say which model or engine you have but if it’s a 4 cyl using oil that is as thick as 15W40 can cause problems with the V-TEC system, and will likely not flow to the rings to keep them cool. A good way to get a Honda to start burning oil is to use the wrong oil in it.

Mine is a 4 cyl regular engine.

5W20 barely existed when my 1999 Honda was made. According to my Honda dealer, it is now the recommended oil for the car, rather than the then-more-common 5W30 that was in the owners manual.

DON’T!!! The engine is not designed for that weight oil; as mentioned, in the Atacama Desert at 110F it would be OK. You need the low starting viscosity ( 5W) to get the oil flowing quickly after start up.

If you lived in Minnesota and parked outside in the winter, it would take about 3 minutes for any oil to reach the valve gear, by which time some bearings would be toast.

Just take the oil to your local recycling depot or give it to someone whose vehicle actually needs it; usually Class 8 heavy duty diesels.

Actually, at near zero temperatures, high viscosity oils will pump up the lifters and fail to allow the valves to fully close resulting in loss of compression. Or that is what I have experienced with customers who used 20W50 oil in an unseasonably cold winter in Mississippi several years ago.

Why would you risk an engine worth thousands to save a few bucks in oil?
Save the 15W40 for the lawnmower. Then if the engine dies you’ll only be out a few hundred at most.

No offense intended to anybody . . .

Is OP the guy that speculated his Plain Jane, regular production, Acura was worth a fortune?