Mercruiser 3.7/LX Coolant Questions

[bryan.kearney]

I am a new boat owner who selected the (I know now) infamous Mercruiser 3.7LX. I am pretty sure I have a coolant leak, but I am always willing to ask dumb questions so here we go:

1) How much coolant should it use in a given 4 hour day of skiing/tubing? I went about 6 trips and then went out and noticed the engine was smoking. I filled it with coolant and it went down about an inch in one 4 hour day.

2) I am putting green antifreeze in, but I am concerned with what it does to the environment. Are there better coolants out there to use if I know I have a leak?

3) Where can I look on the engine to try and figure out where the leak is? Are there common problem areas I should look at? I note something in the bilge water that comes out of plug when I am done for the day, but I dont see a noticeable constant drip at home when it is docked.


Thanks for you help. I am also looking for a "I bought a 470" club to join as well as a "I really own a Bomber boat" club if anyone knows about those

-- bk

 

[180shabah]

Re: Mercruiser 3.7/LX Coolant Questions

1. Engines don't use coolant, if it is dissappearing, it is leaking. Could be internal or external, but a leak is not good.

2. Don't change coolants, find and fix the leak.

3. a standard cooling system pressure test is in order. However, a couple of ares to check are the heat exchanger(do you have the 3" or 4" unit?) and the front cam seal(it will be dripping out the bottom of the timing cover). If it is the cam seal, then a new engine is just aroung the corner if not corrected immediately.

 

[180shabah]

Re: Mercruiser 3.7/LX Coolant Questions

Oops, I forgot...

Welcome to iboats.

 

[stonyloam]

Re: Mercruiser 3.7/LX Coolant Questions

If you are finding coolant in the bilge water, as 180shabah says look for a leak from the front lower starboard side of the circulating pump. There is a tiny weep hole there. It will only leak while the engine is running. You may have to take the engine surround off to get a good look. While you are there make sure that the weep hole is open. If it is leaking from there you need new cam seals. This is a pretty good article on what is involved. http://www.lowerunits.com/470information/470coolantleakrepair.html Welcome to the "club"

 

[bryan.kearney]

Re: Mercruiser 3.7/LX Coolant Questions

Thanks for the information.

180shabah: is 3" or 4" the diameter of the heat exchanger? Also.. is the issue that the coolant will empty out and overheat? If I check it before a day trip is there an issue?

stonyloam: Sorry for the noob question.. but what does the circulating pump look like?

Thanks!

-- bk

 

[guyaverage]

Re: Mercruiser 3.7/LX Coolant Questions

My 470, without a recovery tank tube attached, likes the coolant level approx 1 inch below the cap. Any more and it will force it out. If I fill it all the way, it will lower itself to 1 inch or so below and stay there. It will go all season without needing more.

Some additional places to check for leaks are the intake manifold and the riser gasket. If the two front or two rear intake manifold bolts are even slightly loose, you can lose a lot of coolant (internally into the intake, or external) without noticing much externally. The manifold gasket a cheap easy replacement, I would do that first. If yours is original, its probably in horrible shape. Torque the bolts to 25 lb ft.

Also check your riser gasket. If you have a cast iron exhaust manifold, it may be cracked internally and leaking coolant inside, this is a known problem. If you have an aluminum manifold, your riser gasket should be the newest OEM version which is a thick, graphite covered gasket. Some aftermarket versions are paper or fiber, and they simply dont survive the relative movement between the dissimilar metals of the aluminum manifold and cast iron riser and they leak internally.

 

[bryan.kearney]

Re: Mercruiser 3.7/LX Coolant Questions

guyaverage.. thanks. Does the engine need to be running to see the elaks in these locations?

-- bk

 

[stonyloam]

Re: Mercruiser 3.7/LX Coolant Questions

stonyloam: Sorry for the noob question.. but what does the circulating pump look like?

Thanks!

-- bk

Like this: http://www.mercruiserparts.com/Show...88/35.png&inbr=908&bnbr=170&bdesc=FRONT+COVER the two cam seals are #2 and the weep hole is about where the number "2" is located on the diagram. We are all noobs at one time or another.

 

[bryan.kearney]

Re: Mercruiser 3.7/LX Coolant Questions

Stonyloam: Thanks.. I found it, and the weep hole seems to be plugged up with gunk. I asusme I should try and get he gunk out?

180shabah: It is a 4" hear exchange. If I reach around under and behind it, the metal is wet.. could be with oil.. I am not sure. I see a little bit of oil in the bildge.. but it is pretty dirty down there so I can not tell if it is just gunk I am seeing from the floor.

The coolant I believe is still leaking even when the boat is sitting, but it is pretty slow if it is. There is nothing obviously wet on the top/front of the engine that I see. I will keep digging around.

 

[stonyloam]

Re: Mercruiser 3.7/LX Coolant Questions

Stonyloam: Thanks.. I found it, and the weep hole seems to be plugged up with gunk. I asusme I should try and get he gunk out?

When they are assembled they pack grease between the seals. Just clean out the hole a little with a toothpick or paper clip to make sure that it is open and not crusted over. Sounds like your seals are OK, so far so good. An easy thing to check: Pull the plugs and look at the ceramic around the electrode, it should be tan or light brown, if it is white, you have coolant leaking into the combustion chamber (head gasket or exhaust riser gasket). Most likely to show up on #3 or #4. As said before, you might have a leaking exchanger or bad exhaust riser gasket (#28 in diagram)http://www.mercruiserparts.com/Show...=EXHAUST+MANIFOLD+AND+EXHAUST+ELBOW+(ALUMINUM). You could try putting some dye (any auto parts store) in the coolant and when it is in the water you should be able to see dye coming out with the exhaust if either is bad. If you do see dye coming out, drain some of the raw (not antifreeze) water (aft plug) and see if you have dye there, would indicate a exchanger leak. I know that's a lot of stuff. Good luck.

 

[guyaverage]

Re: Mercruiser 3.7/LX Coolant Questions

guyaverage.. thanks. Does the engine need to be running to see the leaks in these locations?

-- bk

The riser gasket you may or may not see any leakage, if its internal you wont notice anything other than disappearing coolant. Mine never leaked externally, but it definitely leaked internally.

The intake gasket could be either one too actually. I had a leak of about 1-2 drips a minute (externally) while idling, just because the top rear intake manifold gasket was slightly loose (by slightly loose I mean not as tight as the others, maybe 15 lb ft as apposed to the spec of 25 lb ft). This was with the new gasket it place. Before the new gasket was on, I had a lot of coolant making its way internally into the intake back towards the #3 and #4, enough to produce steam out of the carb after a hard run. This gasket is a real workhorse, it blocks off the head coolant passages in the front and back, the exhaust crossover port in the center, all 4 intake passages, and the oily lifter gallery on the bottom. All sealed by this one thin paper gasket. I actually like the 470 but the more I dug into it over the years, I can see why so many are turned off by the voodoo engineering they used to build it.