3.7 Cooling pressure check - dumb question

Alright I am still a newbie here with my little project. History: 1989 mercruiser, 3.7, 165, closed cooling with alpha 1 drive. I have an overheating problem that I am trying to figure out. The boat on muffs starts up and idles fine. The temp goes up steady to about 180 to 200 and then I shut it off. I have done a compression check and everything looks fine and no water in the oil. So I went to Autozone tonight and borrowed a cooling system pressure tester. Sprayed the connections and connected to the filler. Then pumped it up to 17 pounds and watched the needle steadly go down. I pumped it up some more to check for leaks. Then I heard water coming out of the water inlet. Pumped some more and then heard water flushing back through the power steering cooler.

OK, the dumb question is, did I do this test correctly? I even read the shop manual at http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/246

The motor should not be running, correct? I understand that is another test.

If I did do the test correctly then why is it back flushing? Did I miss a step?

Thanks.

Re: 3.7 Cooling pressure check - dumb question

Here is a flow chart for your engine. It shows the seawater path and antifreeze/coolant path.

The power steering cooler should have seawater. You mention you hear water coming out of the water inlet.... are you referring to where you hook muffs to on the drive?

Re: 3.7 Cooling pressure check - dumb question

nwboater45 said:

Alright I am still a newbie here with my little project. History: 1989 mercruiser, 3.7, 165, closed cooling with alpha 1 drive. I have an overheating problem that I am trying to figure out. The boat on muffs starts up and idles fine. The temp goes up steady to about 180 to 200 and then I shut it off. I have done a compression check and everything looks fine and no water in the oil. So I went to Autozone tonight and borrowed a cooling system pressure tester. Sprayed the connections and connected to the filler. Then pumped it up to 17 pounds and watched the needle steadly go down. I pumped it up some more to check for leaks. Then I heard water coming out of the water inlet. Pumped some more and then heard water flushing back through the power steering cooler.

OK, the dumb question is, did I do this test correctly? I even read the shop manual at http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/246

The motor should not be running, correct? I understand that is another test.

If I did do the test correctly then why is it back flushing? Did I miss a step?

Thanks.

Click to expand...

Ayuh,.... My guess is the heat exchanger is holed...

Re: 3.7 Cooling pressure check - dumb question

Agree with bond-o, you did the test properly. If the system is correct the pressure would hold steady, you are pushing coolant out of the system, your exchanger needs to be checked. With the 4" exchanger you can block off a couple of bad tubes and still have good cooling capacity. You can pull the exchanger and pressure check the tubes one at a time.

Re: 3.7 Cooling pressure check - dumb question

Yes, the water is coming out where the muffs go.

Re: 3.7 Cooling pressure check - dumb question

Thank. So this morning I read the shop manual. I pulled the seawater inlet hose off of the heat exchanger and did the pressure test again. Water with coolant mixed in did come out of the inlet nipple. So does that mean the exchanger is toast? How do you pressure test each tube? The Autozone tester only has the large connections. What type of tester would I need or can I use a air compressor and try to block one end?

Thanks

Re: 3.7 Cooling pressure check - dumb question

nwboater45 said:

Water with coolant mixed in did come out of the inlet nipple. So does that mean the exchanger is toast? How do you pressure test each tube? The Autozone tester only has the large connections. What type of tester would I need or can I use a air compressor and try to block one end?

Thanks

Click to expand...

Not necessarily, if it is only one or two tubes, and it is a 4" exchanger, you can plug the bad ones and you should be OK. Thought about it a little, and if you take the caps off of the exchanger and pressurize the system with the pump you should see coolant coming out of the bad tube(s) I think.

Re: 3.7 Cooling pressure check - dumb question

Thanks Terry. I call my local marine shop. They gave me the name and number to a radiator shop they use to test and repair heat exchangers. Hopefulle it will be an easy fix, fingers crossed. We will see next week.

Re: 3.7 Cooling pressure check - dumb question

It will as long as you don't require too many tubes sealed off.... I am a plumber and I've had to solder closed a tube on mine. Clean it up with some emory cloth and 1/2" copper fitting brush.... little flux and some 50/50 with low heat. piece of cake