Mercruiser 470 Coolant Leak

[tc123]

I have a 1987 Mercruiser 470 180HP (330 hrs. on motor) that leaks coolant from around the coolant reservoir cap if I have the reservoir full. If I keep the coolant level 1/2" or so below the filler neck it does not seem to leak. I have changed caps & cap gaskets and checked for any blockage to the overflow tank. The filler neck surface seems OK as well, no nicks or dents. Has anyone else experienced this on this engine and is it OK to run the reservoir less than full? I have no problem keeping the engine cool. It maintains 160 degrees just fine.
Also, I noticed on cold startup that I'm getting a few drops of coolant from the weep hole on the water pump housing. Is this the beginning of the infamous water pump seal leak? Once the engine is running I no longer see any drip from the weep hole. Any advice on this is appreciated. Thanks.

 

[Bt Doctur]

the filler neck on the HX has a crack in it. Any sign of AF from the weep hole is a sign of the seals going bad or the cam being grooved.

 

[nola mike]

the filler neck on the HX has a crack in it.

Filler neck on the HX? Did you mean coolant reservoir? OP, are you talking about keeping it filled to the top of the inner lip (below the level of the overflow bottle hose), or the upper lip at the very top (the cap seals against both surfaces)?

 

[stonyloam]

I am guessing you may have a crack either where the filler neck goes into the reservoir or where the tube goes into the filler neck. Go to Autozone and borrow their cooling system tester. With the coolant level below the filler, pressurize the system and use a little soapy water to see if you can find the leak. If you do, clean it up really well and use some JB Weld to fix it. Yeah, time for new seals, good winter project.

 

[salty3rd]

I have always ran both of my 470 's with the coolant level about an inch below the cap with no issues. I agree the weep hole should be adressed over the winter.

 

[tc123]

Thanks to all for the info and advice. I'll concentrate on the filler neck area to see if I can find something.To nola mike: I filled it to the top of the inner lip (below the level of the overflow bottle hose), not to the upper lip. I was afraid you would all tell me that the water pump cam seals were going south. Not what I wanted to hear but it is what it is. I'm surprised no one has designed an external retrofit water pump for the 470. Running the pump off of the camshaft was not a good idea imho. The 470 is a great running motor except for some of it's unconventional designs (water pump, alternator/regulator,aluminum block & cast iron head, etc.)

 

[stonyloam]

It is WAY easier to just redo the seals than try to figure out some alternate method. Your engine is the same as mine, and my seals have only been done once, not bad for 30 years. Yeah the seals ware out, but conventional water pumps go bad too, just that no one writes in here about it. Look at it this way, with the better seals these days you will probably never need to do it again. Besides the total time needed to do the job is probably way less than the time the guys with the "good" motors spend winterizing every year, I have never seen anyone here complain about a cracked 470 block in the spring

 

[nola mike]

Mine are still original.

 

[Pete104]

Mine are still original.

Mercury may want those in a museum. Watch out!