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5W versus 10W oils

I normally use a 10W-30 oil in my 2000 Grand Cherokee (4L in-line 6). If I change to a lighter-weight oil, will it have any effect on the time it takes to warm the engine on a cold start-up (I live in Ohio)? I’m assuming oil weight has little bearing on “steady-state” heating in the engine.

The 5W and the 10W reflect the WINTER weight of the oil. This means that an engine that has a 5W-30 oil in it will have better lubrication on a cold start-up than it would with a 10W-30 oil. And it’s at cold start-up where a majority of engine wear occurs.


i agree," little bearing on “steady-state” heating "a difference, but rather small.
why change from reccomended(?).
slow cranking in the cold? tired batt. or starter? price?
you’ll wash the parts better, but the design clearances (presumably) requires 10w min. ?

Tester is correct, but neither he or I can tell you what your car should have in it. However there is a neat little book that came with your car. Is called an owner/s manual and should tell you what kind of oil is needed.

His owners manual states 5w-30 or 10w-30 with a PREFERRED after the 10w-30. The recommendation had not changed for a very long time back. The engine itself can tolerate everything from 5w-20 to 20w-50 depending on ambient temp.

Remember, start up is the first 20 minutes of operation. A 5w has the same limits on pumpability as a 10w except -5F colder. That’s not it’s viscosity. At any sensible flow the 10w-30 will tax more power to pump until somewhere above 100F.

No. Cold start-up is the when the engine is first started when there’s no oil pressure. It’s here where the oil pressure must be built up as quickly as possible, and at the same time the oil must flow as quickly as possible. If the oil is as thick as molasis it will build up oil pressure very quickly, but it won’t flow quickly enough to protect engine components during a cold start.


Thanks for all of the feedback. Yes, I was aware that I can use either 5w-30 or 10w-30 per my owners manual. The reason for my question really comes from my brother-in-law, who has a Ford F150 V8 that requires a 5w oil. He says that his truck takes about 15 minutes to warm-up from a cold start and he claims that it due to the lighter 5w oil reducing friction substantially more than a 10w oil does. I don’t believe that the lubricating properties are that different between the 2 oils such that it would impact how quickly the engine warms up. I’m trying to gather information on whether lighter-weight oils cause a longer warm-up period in an engine.

Well? Lack of lubrication to an engine will cause it ot heat up faster, but with the trade off wearing out the engine.

If it’s taking fifteen minutes for the engine to warm up, maybe he should be looking at something like a partially stuck open thermostat causing the long warm-up time.


That makes sense Tester. I’m thinking that the long warm-up must be due to something other than the oil viscosity. How common is a partially stuck open thermostat? Is there anything else that might cause a long warm-up period. He idles the F150 during the warmup, whereas I only idle my Jeep for about 1 minute and then drive it a no more than 35 mph until it fully warms up. My Jeep is putting out warm air typically in about 3 minutes, but I’m driving it during the warmup period.

If I had kept them, I could show you a bushel basket full of the bad thermostats I’ve replaced for this problem. If he’s not getting any heat from the vent system also, I’d be replacing the thermostat.


He idles the F150 during the warmup

That’s his problem right there.

Yep, his F150 is a 2001. But he says it’s always been slow to warm up, even the first year after he bought it new from the dealer.