Not a lot of Water Coming out of Exhaust!

[Myorayacht]

Hey there,

I have a Perkins 50hp Diesel engine in my 36ft sail boat.
Occasionally people stop as we're motoring along and say we have not much water coming out the back of the boats exhaust (has done this since I have owned it) and diesel mechanic hasn't mentioned the problem whilst fixing other minor issues. Motor runs at 900 rpm and 95-100 degrees
Also.. The motor uses about a cup of coolent per trip (3-4 hrs) - maybe this is associated???
Anyway, hope someone out there can help me out!!
Cheers!

[DeepFrz]

Clean the raw water passages from beginning to end. That means from the inlet seacock to the water injector valve on the exhaust system. Have your heat exchanger pressure tested.

[Myorayacht]

Thanks!

[ranger58sb]

Shouldn't lose coolant at that rate.

Check engine temps, but also check pressure cap and overflow bottle for correct functioning...

-Chris

[JK n Smitty]

I would start by inspecting the impellar and than estimate the rate of the exhaust. I do this with a 5 gallon bucket and timing how long it takes it to fill. Than you can compare the rate to what you pump spec is.

Another thing is that the temp seems low. In my experience, diesels run at around 160 degrees. I would get an infrared thermometer and follow this guide from Maine Sail.

Good luck.

Jesse

[HappyMdRSailor]

+1 the IR thermometer.... Find out how hot she's really running.... As DeepFrz also said, get this raw water side flowing... Losing any volume in the freshwater side is absolutely wrong... I suspect you are running above temp.... venting your fresh side past the pressure cap because of running hot... You are slowly killing your engine....

[David M]

The amount of raw water being pumped through the engine has nothing to do with the coolant inside the engine if you have a heat exchanger.

Regardless of how much raw water appears to be flowing through the engine, if your engine is not overheating at a full load for an hour or so, then you have an adequate amount of coolant flowing.

A coolant leak can be indicative of a bad head gasket or a number of other things. Check your engine oil for any emulsification....it will have a brownish coffee latte look to it.

Diesels with a healthy cooling system run at whatever temperature the thermostat was manufactured to open, which the engine manufacturer determines. Mine run at 180 F at a full load.

[model 10]

I was under the impresion that salt precipitates out of salt water at just over 160deg. So does a fresh water temp of say 180, mean the raw water is close to the same temp? If so I suppose that might be a reason for reduced flow near the exhaust elbow on some boats.

[Sailmonkey]

Originally Posted by Guy

I was under the impresion that salt precipitates out of salt water at just over 160deg. So does a fresh water temp of say 180, mean the raw water is close to the same temp? If so I suppose that might be a reason for reduced flow near the exhaust elbow on some boats.

Not even close to 180 for the salt water. It's not in the exchanger long enough to rise more than a few deg above ambient.

[model 10]

How do you explain salt build-up at the injection point in an exhaust elbow? I have seen it down to the size of a pinky.

[SkiprJohn]

Are you really running at just 900 rpm? That's less than 1/2 of normal cruising speed for a 4-108. If its a 4-236 then it is still a bit low.

What does the cooling water look like when you kick it up to 2000 rpm? How does the temp look at the higher speed?

I'd be concerned about losing that much coolant but there might be a simple explanation like cracked hose or collection tank, or something else simple. Check out your cooling system thoroughly.

kind regards,

[Sailmonkey]

Originally Posted by Guy

How do you explain salt build-up at the injection point in an exhaust elbow? I have seen it down to the size of a pinky.

The elbow is a little different than the heat exchanger. Exh gases will be in the neighborhood of 500F. Plenty of heat to cook some salt out.

[Myorayacht]

Wow, everyone is so helpful!

Also, (forgot to mention) a lot of steam comes out of the exhaust... Maybe the water heats up to boiling point?
Anything above 5.5 (hull speed around 6 knots) knots the engine gets up to 110 + degrees Celsius. The gage has a green zone of 80-100.. ?

[gjordan]

100 degrees C is way too hot for a Perkins at just above an idle. The previous suggestion of checking the impeller is the first thing I would do, and then remove the inside tubes of the heat exchanger and take it to a radiator shop for a proper boiling out. When you remove the heat exchanger core, it is a good time to replace the rubber end fittings that hold the core in place. They get old and brittle. If that doesnt improve your water flow, then the exhaust elbow would be next on my list of places to check. Oh yes, the begining of the system(through hull) can be checked simply by taking the hose off of the through hull and opening the seacock. It should put out a surprising amount of water. A 1/2 inch hose puts out a lot of water. If it is just a slow flow or trickle then you have a through hull full of barnacles or some other crud. Any of the suggestions on this thread could prove to be the solution, so just go methodically at it and you will find your problem.___Good Luck_____Grant.

[sww914]

If you continue like this, you'll kill it.
Clean the sea strainer
Clean the heat exchanger, rod out the holes with a wire, if it's bad have it boiled out.
Replace the impeller
Check the exhaust elbow
Check the exhaust for restrictions while you're at it.