Cruising Engine Temp?

Hi,

I got this somewhere else a while ago.

It depends if its raw water cooled or fresh water cooled raw: 160/165.fresh: 170/180

You're on the money. That 5* difference is normal.

Hi,

Does your boat have props and struts or outdrives?

It would be very helpful if you let us know what kind of engine this is and maybe what boat it is in.

As far as changing impellers, close the through hull and change it. If you can change a thermostat you can replace an impeller. While you're at it, clean the strainer.

If this is all a mystery, use Google to search for your engine/boat combination and raw water pump impeller replace.

Dear Dream Catcher,

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Look into your engine manual, but Mercruiser use to have the impeller in the outboard drive...

Is she fresh or saltwater cooled? It sounds exactly like a bad impeller. They should really be changed out each year, 2 at most. Yes it can be changed in water. Open up the waterpump and you'll see it. Go to Google and you'll find complete explanation and I believe video of how to do it. Make sure you get all the fins and pieces thereof which have broken off.
There are two other possibilities that I can think of, especially if she's been run into the sand. 1) The thermostat. I know you said you changed it, but I once ran into a boat that had a little sand come through and we ended up changing the thermostat 3 times. The other is the intakes on either side of the lower unit. Make sure they're clear.

Hi,

Ed - The OP says his boat is FWC which I read as Fresh Water Cooled, how do you figure sand gets into the thermostat on a Fresh Water Cooled System?

You're going to have to haul the boat to change the impellor. You're going to have an impellor in the lower unit of the outdrive. Change both sides. You also may or may not have a raw water pump on the engine and that has an impellor that should be changed if so equipped. Some of the smaller mercruisers only rely on the outdrive water pump to push it through. If this does not solve the problem, then I would look at removing and cleaning your heat exchangers. How high does the temperature get up to over 3000 rpms? There could be other more serious issues causing the temperature to rise also such as blocked/bad exhaust manifold risers, improper ignition timing, or a blown head gasket, etc.......but I would start with the impellors if it's been more then 2 years or 200 hours.

If you cannot physically see the amount of raw water flow out of the exhaust because it is routed out of the propellors underwater. The only way you may be able to see if it's waterflow is to put a gauge in the water line running from the outdrive to the engine, and measure how much water pressure each engine is making at cruise speed. If it has a raw water pump mounted on the engine, you can take the cover plate off and physically look at the impellor, but you might as well change the impellor if you take the cover plate off as they are relatively inexpensive. Less water flow would equal less pressure. You can also measure temperatures of the coolant before and after the heat exchanger, and the temperatures of the exhaust risers with an infrared temperature gun which would give you an idea. The water inlets on the lower unit of the outdrives could also be blocked with barnacles or other growth.

Hi, I think he answered that one already.

Checking the Heat Exchangers is good advice as they may have just furred up while it was sitting for the winter.

Not being familiar with this exact engine arrgt can anyone who is suggest if it is possible to remove the feed hose while the engine is idling and see how much water comes out?

If there is a good flow and it increases as the revs are upped the impeller might be good after all.

As it is a twin engine setup what are the chances of both impellers being duff at the same time?

Long day in the hot sun. I looked back specifically looking fo that and didn't find which is why I asked. Just looked back again and it stood out like a sore thumb. So he's heading for the outdrive and now has some education for his next boat.

50/50

My experience of bad impellers on FWC engines is the other way. When you drive fast, the cooling is sufficient, but when you slow down the heated engine will heat up the heat exchanger where the raw water cooling will be too weak.

Another experience is that the instruments are often showing wrong figures...