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Author Topic:   Questions on cooling system - 2004 Montauk
swist posted 06-07-2006 11:19 AM ET (US)   Profile for swist   Send Email to swist  
I just put my new (to me) 2004 Mtk 170 w/4s Merc 90 (carbed) in the water for the first time. Has less than 100 hrs on it.

All was fine but I have two questions.

1) The Water Pressure gauge is new to me. How does one interpret the reading - there is no "red zone" like on some instruments. It is calibrated from 0-30 (psi?) and once warmed up, seems to hang around in the middle of this range most of the time (couple of hours of trial runs).

2) There is either no telltale or I am looking in the wrong place (that engine is real low in the water w/24 gals of fuel and just one person at the helm). It might be under water. The cooling system is obviously working.


bsmotril posted 06-07-2006 01:21 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
For the pressure gauge, take some notes of where it sits at various engine RPMs. Then each spring, check the current readings against your notes of how the motor was when new. That will tell you the condition of the pump impeller. Right now, just get used to where it reads for various operating conditions, and get used to it so that when it is too low, you'll notice it is not right. Pressure is different for every motor depending on motor mounting height, impeller condition, poppit valve springs, even trim angle. There are no cut and dried readings, even for the same motor on different boats. BillS
Marlin posted 06-07-2006 09:09 PM ET (US)     Profile for Marlin  Send Email to Marlin     
I keep a chart of speed and water pressure vs. RPM in the back of my logbook. Picture at D160_perfdata.jpg
high sierra posted 06-07-2006 10:30 PM ET (US)     Profile for high sierra  Send Email to high sierra     
swist, I have the water temperature and water pressure on my 170 with a 115 Mercury four stroke on it. The water pressure does vary between 5 to 10 lbs. at idle and 30 to 35 at five grand. When there is low or no water pressure, a pump is in order or you have a blocked intake. Water temp runs about 130 to 140. high sierra
swist posted 06-08-2006 09:15 AM ET (US)     Profile for swist  Send Email to swist     
Thanks for the information. Unusual that I've never seen a water pressure gauge on a small boat before.

Any comments on the telltale stream or absence thereof?

high sierra posted 06-08-2006 11:49 AM ET (US)     Profile for high sierra  Send Email to high sierra     
swist, the telltale should be coming out the back of the motor where you could attach a hose to back wash it. Take off the hood and you can see where it is. If you take that hose off and drill a hole on the starboard side of the motor, you can see the flow and attach the hose. It works a lot better for me as I still like to see the flow. high sierra
Marlin posted 06-08-2006 01:02 PM ET (US)     Profile for Marlin  Send Email to Marlin     
Assuming that the 2004 90 4-stroke is generally the same as the 2003 115 4-stroke, the telltale is a few inches above the resting waterline on the centerline of the engine. There is a square-ish plug that fits into the engine housing, and within that is mounted a tube with a diagonal cut in the end that the telltale streams from. With the cowling off, you can use a pair of pliers to twist the tube within the square plug, changing the angle of the telltale.

When I got my engine it was pretty close to straight down, and difficult to see from the helm. I twisted it to about 45 degrees to starboard, and now I can easily see the stream.

Also, the telltale stream on the 115 (EFI) engine is diverted from the cold-side supply and runs through a heat exchanger that cools the fuel. I got into some soft mud, and by the next weekend a little clump of mud had solidified in the heat exchanger, blocking most of the telltale flow. I reamed out the exchanger with a piece of weedwhacker monofiliment, then gave the engine an extensive flush. I don't know if the carburated 90 has a similar heat exchanger.


swist posted 06-12-2006 08:53 PM ET (US)     Profile for swist  Send Email to swist     
Just got back to the boat to check this out, there was water coming out of the backflush port, but it was barely a trickle. Then suddenly about an hour into my last trip I got a full stream.

I suspect something was stuck in the hose - I recently flushed the engine, easily could have been some crud in the hose which wound up blocking the telltale.

The flush attachment is nice - a lot more convenient than earmuffs, but I had no idea it was pumping water back up the pee hole - now I'll know what to check.


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