Volvo MD7A ... Overheating

[Jon Goodyear]

Advice or ideas needed.... My Volvo md7a is overheating when in drive. It's fine when running in neutral at fairly fast revs for an hour or so but when I go into drive and put the engine under load it sets off the overheat alarm after a couple of mins. I have dived under and confirmed there is nothing around the prop. I have oil in the engine and sail drive. There is plenty of water coming out of the exhaust.

The only other thing I can think of is a dodgey temp sender but not replaced this yet as it was fine last season and seems a little odd that it should decide to pack up now.

Any ideas appreciated!

 

[kwb78]

Check that the thermostat is opening and not caked up with salt deposits - it's in a housing on the front of the exhaust manifold and should open at about 60 degrees. It is also possible that the waterways through the engine are blocked. It may be possible to clear them by flushing with something acidic.

 

[Jon Goodyear]

Would that not completely stop the water flow though? I have water from the exhaust at fast revs after an hour in neutral?

 

[VicS]

Would that not completely stop the water flow though? I have water from the exhaust at fast revs after an hour in neutral?

A good proportion of the water flow bypasses the engine going more or less directly to the exhaust to cool that.

The water that cools the engine enters via a connection on the underside of the exhaust manifold and after circulating through the engine leaves via the thermostat, when it opens, rejoining the bypass flow.

Check the thermostat by all means. It should just start to open at the specified temperature. ( see the manual but may also be marked on it) but more likely you will find water passages including/esp those in the exhaust manifold are bunged up.

Owners manual available from VP website if you have mislaid your copy. http://www.volvopenta.com/volvopent...lication_search/pages/publication_search.aspx

Workshop manual at http://www.bluemoment.com/downloads.html

 

[Jon Goodyear]

Thanks folks! Will check the stat and do some descaling and see how it goes! ��

 

[wazza]

VicS & kwb78 why would your suggestions make a difference if the boat is in gear or not???

 

[VicS]

VicS & kwb78 why would your suggestions make a difference if the boat is in gear or not???

Heat will be produced at a much greater rate when running under load. Under no load even if the revs are increased very little fuel will be used and therefore very little heat produced. The engine probably has enough cooling water passing through it to remove the heat under no load conditions but not when under load.