View Full Version : Marine Power 60L Overheats at Idle RPMbs

07-10-2008, 03:29 PM
"I just got a new Marine Power 6.0 L motor installed in my 2860.

The boat runs fine when I first take it out and cruise around, but after an hour if I back the boat down to idle RPM's 700-800 the temp. gauge will instantly heat up to above 200 degrees (normally runs about 150) then as I try to power up the boat appears to be missing.

Once I am able to get back up to even 2000 RPM's the engine runs fine and the temp comes back down to 150 degrees.

I only have about 13 hours on the new re-power and it just started doing this.
Any ideas???

Thanks in advance.

Bayliner 2860
Valdez Alaska"

07-11-2008, 03:11 AM
I just got back from the harbor were I tried a couple of different things.

My boat at low idle (in the boat slip not in gear) is about 600-650 rpm's.
That is when the temp. climbs up above 200 degrees.

As soon as I bump the rpm's up to even 800 it will immediately cool back down to 150 degrees.

It acts like either the sea water pump or the thermastat is not functioning correctly. Both are brand new and there is less than 15 hours on the boat.
I hope the additional information will help.

Thanks again.

07-11-2008, 08:42 AM

Don't assume that because things are new, they don't fail. There is a possibility you have a weak pump but there are a few other things that could be factors as well.

Before you beat your head against the wall you should confirm the actual temp with an independent measuring instrument such, as a laser pyrometer. Those gages, and senders, can do goofy things.

I'm assuming this is an I/B installation. You could have a loose clamp or strainer cap which could be drawing enough air at low speed to effect your cooling. You could have a kinked cooling line which straightens out under the higher pressure of added RPMs. You could have debris or growth on or in your intake system that can not produce enough flow at idle speed.

I would suggest you pull the cooling line feeding the exhaust elbow and check the water flow at 600 RPMs, then at 800 RPMs and compare the difference.

This may shed some light on your problem.

Good luck

07-16-2008, 12:48 AM
"Just got back from working on my boat.

As detailed earlier, my anti-freeze was nearly empty. After a further investigation my overflow tank was way to full and the overflow line from the motor only seems to flow only one way, it does not go back into the motor FWC. Thought it might be a faulty cap (I replaced).

I had someone mention today that my overflow coolant tank needs to be higher than my fresh water cooling unit and it is not it is mounted about eight inches lower than my FWC. He mentioned the anti-freeze will not run up hill to get back to my cooler, is this correct ?

If I need to mount my overflow tank high I can, however it will be difficult to do so with my current setup.

Please advise??"

07-16-2008, 09:39 AM
"No, provided the closed side cap is tight, and working properly, it will create a vacuum when it cools and suck that coolant back into the system. Just be sure the hose on the bottle is connected to the bottom of the bottle and not the top."

07-16-2008, 06:35 PM

Your new information leads me to believe you have a problem similar to one I had. Your overflow should not be full and if it is that is where your antifreeze is going. I would get a radiator tester and take a pressure reading at the heat exchanger. If the pressure reading is higher it indicates a leak between the exhaust and water system maybe in the exhaust manifold or the head gasket (you may want to torque all bolts). The pressure in the exhaust system is far greater than the cooling system and forces the antifreeze into the overflow and than because there is a leak in the system it is not pulled back from the overflow to the cooling system."

07-16-2008, 07:59 PM
"I called the engine distributor today and he suggested checking my FWC filler opening and neck to make sure it had not been damaged.

Sure enough the filler neck had a dent in it probably preventing the cap to properly seal while it was under pressure. I think I have it straightened out now and it appears to be functioning correctly.

Thanks for all the help in trouble shooting my issue. It was very frustrating to have a brand new motor with less then twenty hours on it have these issues.

Thanks again!

Bayliner 2860
Valdez, Alaska"