20hp cooling question

Recently picked up a 1999 20hp merc ob and the lower unit was removed. The cooling tube (from the water pump to the power head) had been removed. One end of the tube is flared and one end is just a straight tube and I am not sure which end goes fits into the power head side. The manual I have does not show that in detail. I did put it together with the flared end into the water pump and someone told me that it should be the other way. I ran the boat after and water did not pee out during idle but had a great, but intermittent flow while it ran at a higher speed. I beleive this motor has a thermostat and not sure if water should pee out all the time or only when the thermostat opens. Any help would be appreciated.

Re: 20hp cooling question

Checked the service manual and it should have the flared end down with the non flared end into the housing on the adapter plate as seen in this link from the parts listing:

Mercury & Mercruiser Parts, Driveshaft Housing Assembly, (20/25/JET 20 SEAPRO/MARATHON 15XD SUPER 15/JET20) (2-STROKE)

Gerry

Re: 20hp cooling question

Make sure the long end of he water tube rides close to the exhaust tube and then the flare reaches away from the exhaust tube then into the water pump. If you reverse this the water tube will be angled and not seal properly spraying water into the midsection rather than a full force stream up into the base adapter plate.

Re: 20hp cooling question

Thanks Gerry. That is the way I did put it together but with the intermittent water peeing out I was not sure.

Re: 20hp cooling question

Thanks Maxz. Not sure if I understand what you mean. The water tube is about 30 inches long and is a straight piece of tubing. It just has one end different than the other. With the intermittent water flow it get me a little nervous.

Re: 20hp cooling question

OK That is good then I havn,t seen that style as ive mostly done 40 - 70 HP. When you say one end is different do you mean diamiter? After looking at gerry,s diagram I see the flange end goes to the bottom at the water pump. (Blown up veiw)I,m still concerned about intermintant flow though. Are you sure you got all the fins from the old impellor out? You should have counted the peices and tryed to reassemble it to make sure it was all there. Peices may have worked there way up into the ports. Ther should be as far as I can see at least a bypass around the T stat allowing water to flow but not enough to keep it cool letting you know the T stat is bad. Also when you put the new impellor in did you replace the metal plate and check the condition of the impellor cup. I was having problems with mine and it would shoot water out the TT then when letting off the throttle the stream would stop momentarilly them work again. I replaced the metal plate in the waterpmp and it works correctly now.

Re: 20hp cooling question

Your engine does have a 120 degree thermostat. see item 35 in this link:

Mercury & Mercruiser Parts, Cylinder Block and Covers, (20/25/JET 20 SEAPRO/MARATHON 15XD SUPER 15/JET20) (2-STROKE)

Once the thermostat has fully opened, you should have a good stream.

Why was the LU removed? Was the impeller changed?

Gerry

Re: 20hp cooling question

Thanks guys for the good information. Maybe I'm worrying about nothing. Seems as though I have the cooling tube installed correctly so that is good. The reason lower unit was removed was to replace a bent prop shaft. I did installed a new water pump impella and when the motor starts very little water pees out (more bubbles out) while ideling but when I run the motor and the thermostat opens the water pees out great (nice big stream), the discharge water is not that hot, but the water will not be a continuous stream (like if the thermostat is closing for a few seconds and opening). I have only owned one other ob and that peed out water continuisly from the moment I started it and thought this would do the same thing.