Is that acceptable if idle speed dropped 20 rpm after oil changed?

[Boater On Thames]

Just found my two Volvo TAMD61A engines both drop 20 rpm after changed the engine oil to SAE40 two days ago. The idel speed comparison:

Before:
Port 585
Starboard 615

After:
Port 565
Starboard 595

 

[rafiki_]

Sounds like your old oil had become rather thin. If your engines are happy at the new idle speed, I wouldn’t worry.

 

[Momac]

Sounds like your old oil had become rather thin. If your engines are happy at the new idle speed, I wouldn’t worry.

Or perhaps the new oil is too thick?

Has the correct grade of oil been used ?

 

[[2068]]

Was there a special reason for SAE 40?
15W/40 is more usual.

 

[stelican]

Was there a special reason for SAE 40?
15W/40 is more usual.


View attachment 96349

Global warming !

 

[Sticky Fingers]

Was there a special reason for SAE 40?
15W/40 is more usual.


View attachment 96349

This

Thank you Scala. I was thinking to order the local brand VDS3 oil. Then I learned that their TBN usually around 9-10 only. It is better suit modern high speed engine with low sulphur fuel I think. And it might not good for my engines because I only use it almost always 600-1000 rpm only on the river and use very little hours. So I decided to use the old school SAE40 thick mineral oil instead. Then when comes to the coolant, I found there is no such product call anti corrosion additive for engine. Only found some general correction inhibitor for central heating system and commercial cooling system. I think it should be no different between engine metal or commercial metal or home metal. As long as the inhibitor is for all kinds of metal. I might be wrong, so that is why I am here to ask.

 

[[2068]]

What are the ambient temperatures where you are?

 

[Sticky Fingers]

He’s on the Thames.

 

[andy59]

Lucas i think you are trying to fix a problem that doesn't exist, if your tickover has dropped now with that oil, what will it be like in winter @ 5 degrees ?. Just stick 15/40 in and forget about it.

 

[[2068]]

He’s on the Thames.

SAE 40 is fine for Dubai, possibly not the best choice for the Thames in January.
???

 

[Momac]

Whats the thinking that leads to deviate from the 15W40 grade if that is the recommended oil for your engine?

 

[peteK]

As others have said that oil is to thick,just use 15/40

 

[rotrax]

At normal operating temprerature a straight 40 grade will be the same viscosity as a 15/40.

At cold/start up temperature it will be more viscous.

If the OP's engines were not at normal temperature, the increased drag of a more viscous oil would drop the RPM.

Old oil can be less viscous than spec. if it has had lots of use and contains contaminants, so even new 15/40 migh have the rev drop effect.

 

[Momac]

................ even new 15/40 might have the rev drop effect.

I don't think most people have the capability to measure engine revs within 30 rpm so you may well be correct.

 

[Boater On Thames]

Great. Thanks a lot every one. Now I have a peace in mind.

Will keep monitoring the performance. And report if found anything else.