[rice]

hi everyone. i just picked up a single cylinder 5hp mariner for a kicker for my fishing boat. i believe it is early 90's but not too sure as i cannot find the model number. it started first pull, and ran good in a bucket. but the motor runs extremely hot. it has a telltale that has alot of flow but the water coming out seems to be about the same temperature as the water in the bucket. it does not seem to be removing the heat. when i put a bit of water on the head after idling for about 10 minutes it started to steam. if i put water on the exposed part of the spark plug just after the rubber cap it almost sizzles. you cannot put your hand there for even a miliseccond.

does anyone know if there would be a thermostat in there somewhere? i have done some searching and i dont think there is one.

does anyone know if small single cylinders like this are supposto run hot like this?

any ideas?

thanks in advance

[rice]

too many threads. hard to get attention.
please help

[rice]

anyone????

[emckelvy]

Definitely should not be running that hot. Don't think it has a thermostat but without a serial number hard to tell. Check all over the block for stamped numbers or something that looks like a ser #.

Take a look at the various parts diagrams for 5HP and maybe you can find your motor:

http://www.mercruiserparts.com/Selec...asp?class_id=2

If you find the motor has no thermostat, most likely the overheating is being caused by a blown head gasket or plugged cooling passages. You'll have to remove the cylinder head to inspect for that.

Be sure to install a new head gasket and also check the head for warpage by laying a straightedge across it in various positions and see if you can slip a thin (approx .001" or .0015") feeler gage under the straightedge.

If the head gasket is obviously leaking or the head is warped, the head should be 'surfaced' to ensure it's perfectly flat.

This can be done by a good automotive machine shop, or you can take some medium-grit sandpaper and 'dress' the head on a flat piece of glass.

It's probably quite easy to pull the lower unit off, you could inspect the impeller and blow compressed air up the water tube to check for obstructions while the head's off.

Note that the head bolts should be torqued upon reinstallation. Re-torque the bolts to specs after you run it for the first time and it's cooled down. And it's a good idea to re-torque the head bolts once a season after that. Put a thin coating of waterproof grease or Permatex Aviation-type Gasket Dressing on the head bolts to keep them from seizing-up in the block.

Let us know what you find out..........ed

[rice]

thanks for the reply emckelvy. the head gasket was fine, no warpage, i cant see a thermostat anywhere. the engine is still running ok just hot. the water passages are all clear. it looks brand new in there.

there is a silver shiny disk about the size of a thermostat on the side of the block. does anyone know if there might be a thermostat behind there and if so how to get it out. i dont know what elce it could be. its just a round silver disk about the size of a loonie. it looks like its just pressed in there. thanks again for the help

[emckelvy]

The silver disc may be for the model serial #, is there anything printed on it?

And it's probably time to pull the lower unit and check the impeller and pump housing out, blow air up the water tube, etc. to try and narrow down the problem........ed