Burning oil ?

[dreadnought]

Hi guys,I have a bmc 1800 in my narrow boat and always use classic 20/50 engine oil and it never used a drop, this last oil change I was told by an engine "expert"that I should be using 15/40 oil, but since using the different grade its using oil,not leaking as I can see so it must be burning oil,do you guys think it's a coincidence it's using oil or is it down to the oil,any ideas?many thanks..

 

[Tony Brooks]

Well, 15W40 is a "thinner" oil than 20W50, both hot and cold, so if the engine is worn that might be the problem. However, I would like to see the API specification in case you have got hold of an oil that has cleared all the carbon from the pistons.  I would not expect the change to cause such a problem in most engines because originally the grade recommended was SAE30 that is "thinner" still when hot.

[alan_fincher]

On 10/07/2024 at 13:02, Tony Brooks said:

I would not expect the change to cause such a problem in most engines because originally the grade recommended was SAE30 that is "thinner" still when hot.

 

In the BMC 1800 Handbook I still have an original copy of the recommendation is actually always for a multigrade, (mostly but not exclusively 20W-50).  None of the recommended oils for UK temperatures is actually a monograde.

When we had a boat with a BMC 1800 we always used a 20W-50.

[Tony Brooks]

3 minutes ago, alan_fincher said:

 

In the BMC 1800 Handbook I still have an original copy of the recommendation is actually always for a multigrade, (mostly but not exclusively 20W-50).  None of the recommended oils for UK temperatures is actually a monograde.

When we had a boat with a BMC 1800 we always used a 20W-50.

 

True, but the basic design goes back to the B series petrol engine and multigrade oils were not available when they were designs, they were rare when the 1.5 diesel first appeared.