Can using the wrong oil weight hurt an engine?

[vi edit]

I've always put 10w-40 in my cars 9 months out of the year, and 10w-30 in the winter. I changed the oil for the first time in my VW Passat w/ the 2.8L V6 and put in 10w-40.

As I was flipping through the manual looking for the proper coolant to purchase, I found that VW recommends 5w-30 oil. Would using 10w vs. 5w harm the engine in any way?

 

[Bleep]

NO

 

[Evadman]

Originally posted by: Bleep
NO

yes

Will what you chose damage it, doubtful. If you chose 90 weight, you can bet your butt you would damage it.

 

[vi edit]

That's reassuring

In the future I'll go with 5w, since it's not *that* much more expensive, I just wanted to make sure that the engine wasn't going to sludge up in the 3000 miles that this oil change will last. I was looking over at a VW specific forum on an engine oil thread and some of the guys over there made it sound like the end of the world if you put in 10w oil.

Then again, these are guys that spend more on one bottle of synthetic oil than I did on 5 quarts of my Quaker State Performance "real" oil.

 

[Mark R]

On most cars, the cold viscosity (the number before the W) makes little difference - the hot viscosity is more important.

Too high a viscosity (too thick) and the oil won't protect at high engine speeds. Too low and the oil pressure will not be high enough to lubricate all the critical parts. In most cars, however, you can go 10 either way with little problem.

One important exception are Ford cars, with the Zetec engine (e.g. focus). There is a design flaw in the Zetec engine which causes the valves to stick - rather than fix the problem, Ford just changed the recommended oil - from 10W40 to 5W30. The use of 5W30 oil is critical in this engine. If you use 10W40 the valves will stick, causing poor performance, and damage to the catalytic convertor. If you use 0W30 oil, the engine won't start (0 weight oil won't develop enough oil pressure, and the ECU treats this as a critical fault and cuts the ignition).

The most important thing though is to check that your oil meets the minimum standard for your engine - for all but the newest VWs, most oils are good enough - but for many manufacturer's latest gen engines, the specification of oil is extremely tight - you need to check that the specifications of the oil are exactly those that your engine requires.

 

[rahvin]

Originally posted by: Mark R
On most cars, the cold viscosity (the number before the W) makes little difference - the hot viscosity is more important.

Too high a viscosity (too thick) and the oil won't protect at high engine speeds. Too low and the oil pressure will not be high enough to lubricate all the critical parts. In most cars, however, you can go 10 either way with little problem.

One important exception are Ford cars, with the Zetec engine (e.g. focus). There is a design flaw in the Zetec engine which causes the valves to stick - rather than fix the problem, Ford just changed the recommended oil - from 10W40 to 5W30. The use of 5W30 oil is critical in this engine. If you use 10W40 the valves will stick, causing poor performance, and damage to the catalytic convertor. If you use 0W30 oil, the engine won't start (0 weight oil won't develop enough oil pressure, and the ECU treats this as a critical fault and cuts the ignition).

The most important thing though is to check that your oil meets the minimum standard for your engine - for all but the newest VWs, most oils are good enough - but for many manufacturer's latest gen engines, the specification of oil is extremely tight - you need to check that the specifications of the oil are exactly those that your engine requires.

Believe it or not but most of the multigrade oils are pretty much the same these days. After the purification and the addititives most oils have the same range they just slap the different labels on bottles so poeple can buy the "right" oil. In a modern oil (purchased today) there should be almost no difference between 5w-40 and 10w-30. They will maintain their viscosity through the same temperature ranges as the other "grades". Now this isn't true in every case but the oil is so good these days you can almost count on it.

Most oil is nearly as clean as synthetics these days, I remember when the stuff I poured the crank case was a light brown, these days it looks like Karo Syrup.

 

[ObiDon]

I remember when the stuff I poured the crank case was a light brown,

Ha ha! I remember those fat cardboard/metal cans you had to jam the spout into! It's a good thing I was too young to have to fuss with those. I'm not always the most patient person.

 

[Mark R]

Actually, with the trend for longer and longer service intervals - several manufacturers are now specifying 15 - 20k mile oil change intervals - the additives are of critical importance.

Why would MB have gone to the expense to develop a new oil specification especially for their latest engines? Is it just through spite that they will void your warranty if you don't use an approved oil, or is there a reason for it?

For example: only 3 oils meet the latest MB spec 229.5 (for the latest engines) - anything else will shorten the life of your engine.

Have a look at this site, which lists a number of oils and their manufacturer's approvals:
http://www.whnet.com/4x4/oil.html">link</a>