Diesel Oil in Gasoline Engines

[MAC]

I was at a STS tire center yesterday and happened to get onto the topic of using diesel oil in older engines. The person behind the counter said that he formulated oil for 30 years and that it would not be wise to use diesel oil in a gasoline engine. I mentioned that a GM powertrain engineer (the Guru) said it’s acceptable to use diesel oil in pushrod engines and engines with older technology in order to introduce additional ZDDP (zinc dialkyl dithiosphosphate). He said don’t do it because diesel oil has other additives which aren’t compatible with gasoline engines and these additives could ruin the engine. I looked at him with a doubtful look, which he noticed. He then said to go ahead and use diesel oil, but as a friend I’m telling you don’t because diesel oil it’s not made for gasoline engines and it can cause problems. I have put a couple of quarts of Shell's Rotella diesel oil in my Northstar but have never drained and filled with Rotella. I was told by the STS sales person to not put any diesel oil in gasoline engines.

Interesting how different people can have opposite opinions.

[adallak]

Do not listen to a person behind the counter. They usually know nothing.

[Ranger]

This is from the ZddPlus link that BBF posted in the EOS thread.

" Why Can't We Use Diesel CI/CJ-4 Rated Oils?

There are some diesel engine rated oils on the market which may still have some ZDDP in them. There are problems associated with using these oils in a normal gasoline engine which can become severe in a high-performance gasoline engine. One issue is the high amount of detergent additive, and another is the high viscosity.

High detergent oil has a lower surface tension and lower shear pressure rating which can cause higher bearing wear in gas engines. A diesel engine needs oil with very high detergent capabilities in order to hold the large amount of combustion byproducts in suspension, but it is not optimized for a gasoline engine. The bearing journal size-to-displacement ratio on a gasoline engine is designed around the use of a lower detergent oil and relies on a high-shear rating to the oil. The additional detergents required for soot control actually reduce the effectiveness of added levels of ZDDP found in diesel oils. Also, newer diesel oils beginning in 2007 have greatly reduced their content of ZDDP.

The other problem with high detergent oil is that it actually reduces the friction reduction that the ZDDP affords, especially in a high-performance, high valve spring pressure engine.

The viscosity rating of most diesel rated oils is higher than optimum for our higher revving gasoline engines, and can cause oil starvation in bearings at high rpms.

"

[JasonA]

I wouldn't use a diesel oil if it wasn't also certified in spark-ignition engines. Most diesel oils are certified for both compression-ignition engines (diesels) and spark-ignition engines (gasoline). That's the "SL" or "SM" rating on the bottle. If the "diesel" oil also has an SM rating, it's perfectly safe for your gasoline engine.

[JasonA]

This is from the ZddPlus link that BBF posted in the EOS thread.

...

There are some diesel engine rated oils on the market which may still have some ZDDP in them. There are problems associated with using these oils in a normal gasoline engine which can become severe in a high-performance gasoline engine. One issue is the high amount of detergent additive, and another is the high viscosity.

That seems to be directly at odds with what they're trying to sell (ZDDP boost for gasoline oils). All of a sudden, now that SM oils have little-to-no ZDDP, it's a foreign substance. Never mind that our oils used it for years. They have much to gain by scaring folks off diesel oils in favor of using gasoline oils and buying their product for the ZDDP spike.

And the viscosity claim -- absolute BS. In fact, most "high performance" engines use higher viscosity oil. Many hi-po European makes specify 0W-40 synthetic oil for their cars.

[kcd1184]

This is from the ZddPlus link that BBF posted in the EOS thread.

" Why Can't We Use Diesel CI/CJ-4 Rated Oils?

There are some diesel engine rated oils on the market which may still have some ZDDP in them. There are problems associated with using these oils in a normal gasoline engine which can become severe in a high-performance gasoline engine. One issue is the high amount of detergent additive, and another is the high viscosity.

High detergent oil has a lower surface tension and lower shear pressure rating which can cause higher bearing wear in gas engines. A diesel engine needs oil with very high detergent capabilities in order to hold the large amount of combustion byproducts in suspension, but it is not optimized for a gasoline engine. The bearing journal size-to-displacement ratio on a gasoline engine is designed around the use of a lower detergent oil and relies on a high-shear rating to the oil. The additional detergents required for soot control actually reduce the effectiveness of added levels of ZDDP found in diesel oils. Also, newer diesel oils beginning in 2007 have greatly reduced their content of ZDDP.

The other problem with high detergent oil is that it actually reduces the friction reduction that the ZDDP affords, especially in a high-performance, high valve spring pressure engine.

The viscosity rating of most diesel rated oils is higher than optimum for our higher revving gasoline engines, and can cause oil starvation in bearings at high rpms.

Larry,

Hi. What, in your opinion, does a person need to use for oil, or oil and additive in a 1994 N*?

If you would rather not go fishing (can of worms) on line, get me your #(Ithink I still have it though) and I'll give you a jingle.

Kent

"

[Ranger]

This is from the ZddPlus link that BBF posted in the EOS thread.

...

There are some diesel engine rated oils on the market which may still have some ZDDP in them. There are problems associated with using these oils in a normal gasoline engine which can become severe in a high-performance gasoline engine. One issue is the high amount of detergent additive, and another is the high viscosity.

That seems to be directly at odds with what they're trying to sell (ZDDP boost for gasoline oils). All of a sudden, now that SM oils have little-to-no ZDDP, it's a foreign substance. Never mind that our oils used it for years. They have much to gain by scaring folks off diesel oils in favor of using gasoline oils and buying their product for the ZDDP spike.

And the viscosity claim -- absolute BS. In fact, most "high performance" engines use higher viscosity oil. Many hi-po European makes specify 0W-40 synthetic oil for their cars.

Yeah, I have to take what they say with a grain of salt as it is self serving. I should have said that, but figured it was evident.