INBOARD/STERN DRIVE

EXHAUST MANIFOLD TIPS

Exhaust manifolds can cause all sorts of grief to your Mercruiser, OMC, or Volvo if not maintained properly. I advise the installation of a "fresh water" cooling system on your outfit where available. With that, 98% of cooling system problems can be avoided. A fresh water cooling system is set up similar to the radiator on your automobile. The engine coolant is passed thru a heat exchanger that is supplied with outside raw water by the water pump in your outdrive unit. The engine coolant uses the same antifreeze as your automobile so there is no problem with freezing and cracked components in colder climates.
BUT - the RISERS are still raw water cooled as the raw water is dumped thru them to cool the exhaust. They MUST be drained for winter (and the manifolds also if raw-water cooled). They can also become filled with corrosion scale over time and restrict the water flow through your motor. If your motor is running hot this is the FIRST place to check after the thermostat & impeller. Engine circulating pumps are sometimes a concern, but because they have stainless vanes, they usually don't become a problem as far as overheating although they WILL eventually wear out the internal seal, just like in a car, which will be evident by the water dripping from the pump (this will cause failure and overheating).

If the risers are not corroded through, you may clean them as follows:
Obtain a gallon of Muriatic acid and a large box of baking soda. Fill an adequate size container with enough water to dilute the acid to one quarter strength and immerse the riser in the solution.

WARNING!!  Only do this OUTSIDE and in a well-ventilated area. Fumes are corrosive.
This acid is very corrosive and WILL damage anything else it touches including YOU! Do this at your own risk.

Leave the riser in the solution until it stops bubbling. You may add more acid as the process continues. Then neutralize the solution (and the riser) with the baking soda before you dispose of it.
You may be able to further clear the small holes in the exit part of the riser with a large screwdriver or similar.

It's also possible to have a radiator shop "tank" your risers & manifolds to get rid of scale & corrosion if  they're not too far gone. This may give you a few more years' use also. This is a safer, though more expensive, way to clean up your manifolds & risers.