Engines, steam and mechanics

[hillyarder]

There was a post some time ago about white "smoke" from the exhaust. I have a petter 12hp circa 1966 which until recently had not run for 2 years. she started first time and is desperate to run. does not misfire and has run for 10 hours solid. however very little water seems to come through the exhaust but there is some steam. the water is often black (not oily) but does clear. the noise from the exhaust is the sound of a steam engine. there is no silencer. the engine runs ok but as i say the water flow looks like it should be more and it did get very hot recently after prolonged running. i thought thre might be a problem with the thermostat but as yet have not had time to check.
any advice would be appreciated especially as to flow (the seacock is fine). or does anyone know a good mechanic in the chichester area i could use.

thankyou in advance

 

[maris]

I don't have any experiance of your particular engine, but the basics are mutch the same. On the water inlet side of the engine there is usualy a pump, (some times belt driven but normaly mechanical). In side the pump you will probably find a rubber impeler, they have a habit of sticking if the unit has been idle for a while. When the engine is next run the impeler starts to break up giving poor water circulation. This would also make the water black as bits of rubber get flushed out. A deisel engine is more tolerant to over heating so you might not notice any diference in how the engine runs untill major damage has been done. I would not run the engine untill the problem has been sorted. When running the engine it is always a good idea to check the flow from the exhaust from time to time.

 

[jfkal]

Good idea to change the impeller. Seems to be the most likely source of your problem.

 

[vyv_cox]

In addition to checking the pump, ensure that the water branch to exhaust manifold is clear. If this is blocked it may back-pressure the pump, wearing seals and possibly filling the sump with water, on some designs.

 

[WayneS]

I had a similar problem last week. In my case an engine mount had collapsed and, as the water pipe run under the engine, it became crushed and restricted the water flow. Silly but true.

Wayne

 

[oldharry]

Lack of water from the exhaust, + steam, + overheating engine = insufficent coolant flow. Check impellor (very likely to be damaged after 2 years unused), obtructions to the water inlet, kinked or crushed water pipes, or some sort of blockage in the water supply to the engine. (Check it all the way through - it doesnt always block in the obvious places if something has been sucked in to the water inlet.

If a rubber water impellor is fitted, check the housing is not damaged, as heavy scoring or wear dramatically reduces the efficiency of the pump. Some have a sacrificial s/s plate fitted which is replaceable in preference to the whole housing.

Soot in the water in this situation is normal. Its usually flushed through in such small quantities that you dont notice it.

Unlikely to be the thermostat, but thats the next thing to check if all else is OK.

Rather more difficult to deal with on an old engine is clogging of the internal waterways with either mud or solidified salt. I should say a LOT more difficult as it involves taking the cylinder head off, then a lot of careful poking and scraping around the water jacket and cylinder head waterways. This only should be considered after all the other elements of the system have checked out 100% OK.

Check too for corrosion around where the water is injected into the exhaust. Hot sea water is highly corrosive to metal, and failure here causes all kinds of problems.

Excessive back pressure in the exhaust system due to a blockage can have the same effect. You mention it sounds like a steam engine when running? If the exhaust is made of rubber diesel hose and has been run short of water, the internal liner fails and blocks it off and can stop the engine dead. The back pressure can overcome the water pump and prevent water circulation. Take the hose off at the engine manifold end. If the internal surface has a folded ribbed appearance, then it needs replacing - and may possibly solve the problem! These rubber pipes should NEVER run more than hand hot or they rapidly fail.