Oil change temperature

[Montemar]

I have always assumed that engine oil should be changed when hot but with multigrade oils the opposite must be true as viscosity is least when cold.
Am I missing something?

 

[Robert Wilson]

I have always assumed that engine oil should be changed when hot but with multigrade oils the opposite must be true as viscosity is least when cold.
Am I missing something?

I dunno, but I'm interested to hear the answer(s)

Thanks for posting this.

 

[spannerman]

In the dealers I have worked in we always did it hot as its definitely easier to extract and having run the engine the oil has most of nasty stuff in suspension so it comes out with the oil.

 

[About Time]

Hi,

When engine oils get warm they thin out. This goes for both single grade and multigrade. However the difference in viscosity is bigger in single oil. I found this very informative article for us - scroll down to 'what is multi-grade oil' if you want the quick information

http://www.kewengineering.co.uk/Auto_oils/oil_viscosity_explained.htm

 

[Montemar]

Thankyou for your replies.
If the oil is not too old and not completely lost its viscosity range then perhaps it is possible to run the engines, stir up the detritus so it is in suspension, then pump out. The alternative is to take the boat out to warm up the engines consequently I will try it cold and hope my electric pump can get it out. I wonder if doing an oil change with a hot engine is partly a throwback to the past and partly because it "feels" right.

 

[rafiki_]

Thankyou for your replies.
If the oil is not too old and not completely lost its viscosity range then perhaps it is possible to run the engines, stir up the detritus so it is in suspension, then pump out. The alternative is to take the boat out to warm up the engines consequently I will try it cold and hope my electric pump can get it out. I wonder if doing an oil change with a hot engine is partly a throwback to the past and partly because it "feels" right.

You should always warm the engine before changing the oil if you can. It dramatically speeds the extraction.

 

[sarabande]

Dynamic and Kinetic viscosity fall as temperature rises.

Pretty pictures and tables here .

http://www.viscopedia.com/viscosity-tables/substances/engine-oil/

 

[Montemar]

Thanks folks, I checked it all out and find I have fundamentally misunderstood the SAE multigrade ratings.
10W-40 means the viscosity of oil when cold is the viscosity of SAE10 single grade oil and when hot is the viscosity of SAE40 single grade oil. However when SAE40 oil is hot its viscosity is less than SAE10 oil when cold despite it being a thicker oil.
Thus 10W-40 oil gets considerably thinner at high temperature but is thicker than single grade 10 oil at high temperature.
So it looks as if I will have to take the boat out before the oil change so only need some decent weather.

 

[VicS]

Thanks folks, I checked it all out and find I have fundamentally misunderstood the SAE multigrade ratings.
10W-40 means the viscosity of oil when cold is the viscosity of SAE10 single grade oil and when hot is the viscosity of SAE40 single grade oil. However when SAE40 oil is hot its viscosity is less than SAE10 oil when cold despite it being a thicker oil.
Thus 10W-40 oil gets considerably thinner at high temperature but is thicker than single grade 10 oil at high temperature.
So it looks as if I will have to take the boat out before the oil change so only need some decent weather.

But if you take the boat out you will have to rig up some kind of cooling water supply while you warm the engines up and run them for long enough to warm the oil right through.

 

[Montemar]

No, the engines have a cooling system - it is a motor boat.

 

[Surfacesub]

In the dealers I have worked in we always did it hot as its definitely easier to extract and having run the engine the oil has most of nasty stuff in suspension so it comes out with the oil.

It is also sound engineering practice to bring the engines up to temperature by loading them, which will accelerate engine temperature rise. Given the current media issue with pollution I shudder to think of the effect of marine oil changes if the engines are heated/warmed during the process of incomplete combustion. I appreciate it's not always possible but I usually drain the oil on the return of my last trip of the season. Furthermore you would be surprised at how much oil drains after the sump is empty, when left for a few days, it all helps the effectiveness. In addition if I intend laying up for a prolong period I have been known to change the filter and with sufficient new oil to reach the pick up, run the engines for a few minutes to purge the galleries. The longer you can then leave the final drain obviously the better.

 

[QBhoy]

There should be no doubt here...
100% drain or change the oil when the engine is warm and if possible, as soon after it's stopped (after a good run) as possible. Best to get all the suspended stuff out with the rest asap.

 

[DavidJ]

I've tried some of the cheap car type pumps in the passed and they are generally quite pathetic and the oil gets cold meantime making them more pathetic. So I bought the Marco OCK1 12volt and I can drain one hot engine (10 litres) in about 15 mins
The Marco is badged up by companies like Cleghorn Waring (called the CW220) who charge £180 but if you go to pumpsandpowerwashers.co.uk they are £98
For me it makes an oil change nearly a pleasure.