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stevedal...
stevedal...

Posted: Wed May 18, 2011 12:45pm

Post Subject: Oil Type for thornycroft 80D

Hello, I've recently installed a second-hand Thornycroft 80D (20years old) in my boat and all seems to be working fine. However I'm concerned about oil suitability. The manual that came with the engine lists oils which appear to be non-existent. Any ideas please? the engine is based on a Mitubishi K4. Also, the engine temp won't rise above 60deg. Any ideas here? Stuck thermostat possibly? Many thanks

Tony-B...
Tony-B...

Posted: Wed May 18, 2011 4:44pm

Post Subject: Oil Type for thornycroft 80D

First the temperature. Some marine conversions were fitted with a low temperature thermostat to avoid scalding water being supplied from a calorifier. A direct, raw water cooled engine would also have a low temperature thermostat fitted to minimise the formation of internal scale. You should be able to fit a hotter thermostat but remember someone may have taken the stat out or fitted a low temperature one to try to cover up overheating problems. Unfortunately Thornycroft do not seem to put manuals on-line so unless you tell me the oil grade you can not get I can not help much. I have no problem obtaining HD30 or SAE 20W50 in API CC from motor factors. There may or may not be a problem using a higher specification oil than that specified - especially in canal use. There is some indications that using an oil with a large additive pack just might contribute to bore glazing but this is by no means certain and much depends upon the design of a particular engine as well as how you run it. If I tell you that you can use an oil different to that specified by Thornycroft and your engine fails I would be laying myself open to a negligence claim and I am not willing to do that. I suggest that you contact Thornycroft and ask them. They do have a website. If this helps my 20 year old engine specifies SAE30 in API CC. I have been trialling SAE 15W40 in API CF for over a year without any apparent Ill effects but I am NOT saying that you can follow suit. Tony Brooks

stevedal...
stevedal...

Posted: Wed May 18, 2011 6:13pm

Post Subject: Oil Type for thornycroft 80D

Many thanks for your swift reply Tony. As yet I haven't taked off the top of the water pump, so it'll be interesting to see what, if anything, is in there! The engine was originally in a Springer, which makes me think it was skin-tank cooled. My original engine was air-cooled and I have had 2 x skin tanks welded on the outside of the swims to accommodate the newer engine, giving approx. 9cu ft of cooling space. The oil specified by Thornycroft was API CC at I believe 10w-30 (I don't have the manual to hand). Morris Lubricants can supply an API CC/SF at 10w-40. Their advice is that it should be suitable. Bearing in mind the age of the engine I a wary of taking any chances! Thanks again.

Tony-B...
Tony-B...

Posted: Wed May 18, 2011 6:51pm

Post Subject: Oil Type for thornycroft 80D

For the record Beta say you need 1 sq ft of skin tank area per hp and I had calculations done that came out at 1 sq per 3 HP. Both are near enough to confirm each other. The API specification for both the oils you quote are the same so that eliminates the bore glazing thing. We are just left with a slightly thicker oil when the oil is hot. I can see this as nothing but a slight advantage in an old engine but I must refer you to makers again for a definitive answer. Tony Brooks

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