mercruiser coolant boiling

[sbuckx]

I had an annoying problem all last season, that I am going to try an nail down this year. My mercruiser 190 would boil over the anti-freeze into the plastic tank on the side without actually overheating the motor. I tried not to let it lose so much that the temp would get above normal.(I sucked it back out and re-added it) Here is what I tried. I removed the thermostat and tested it, also left it out , changed the impeller,changed pressure cap, and made sure all of the hoses and heat exchanger are clear. I seem to have good flow on the lake water side. And I assume also on the closed side because it never really gets hot until level gets dangerously low. The mixture is 50/50 on the closed side. I had a mechanic tell me that I may have a small leak somewhere that is causing it to lose pressure and boil at a lower temp. I was going to borrow a pressure tester this spring at test that out. Anyone think it may be something else? Any input would be greatly appreciated. Thanks

 

[snapperbait]

Re: mercruiser coolant boiling

Any bubbles or foam in the coolant? If so, might be a blown head gasket..

 

[magster65]

Re: mercruiser coolant boiling

Yeah, head gasket maybe or I've seen this happen from having a trapped air pocket in the motor.

 

[johnkc]

Re: mercruiser coolant boiling

did you check the hose from the drive to the transom assy. if it has been replaced make sure that it is not too long as it will kink.

 

[sbuckx]

Re: mercruiser coolant boiling

Thanks for your reponses.<br />I did change the hose from the transom and that did not work. My first thought was head gasket, but there is nothing in the oil, it has been clean, no water. Air pocket? How can I determine if there is one. I tried adding coolant like the book says. I let it run at a certain rpm and added to the bottom the filler neck, or whatever the book says, can't remember. I wouldn't say that there is foam, but it is definitely bubbling like it is boiling. It runs great, but this is a pain. Also, if I catch the boil over before it overflows the plastic tank, I can account for just about all of the coolant. Thanks again

 

[DJ]

Re: mercruiser coolant boiling

sbuckx,<br /><br />Removing the thermostat will not help your situation. <br /><br />I think that you may have an issue with the cap on your heat exchanger (radiator). The cap is supposed to hold the system at a certain pressure. If the cap does not do that, the coolant will boil at a much lower temperature than coolant under pressure.

 

[Bondo]

Re: mercruiser coolant boiling

With the bubbling you describe, I'd be looking into the head gasket.... It's leaking into the cooling system... Depending on Where it Failed, it May not leak into the oil, or to the outside....

 

[sbuckx]

Re: mercruiser coolant boiling

Based on what I have already tried and what your posts are telling me. It looks like I should seriously look at the head gasket. Since changing it is more work and hasle than I want to get into myself, can anyone give me an idea of how much $$$$ I can expect if I take it to my local boat shop. You know, like the comercial, I don't want to pay too much.

 

[sbuckx]

Re: mercruiser coolant boiling

OK the saga continues.. I pulled it out of storage and noticed that my coolant was laying in the bilge. It looks like it leaked out of the front of the motor somewhere near the water pump. I can tell this because it is wet on the floor near the front motor mounts. Anyway. Does anyone think that the water pump may be causing the bubbles or foam(although I don't think there is much foam)? If it is sucking air is it possible? I haven't started the motor yet this year, I don't know how bad the leak is.

 

[MrBill]

Re: mercruiser coolant boiling

You indicated that your engine was a Merc 190. If it is the in-line four cylinder, 4 bbl 3.7 liter 190....then the issue could be seals at the water pump. If you are indeed leaking coolant toward the front of the engine check for leakage out of a small hole on the underside of the water pump. The hole is there to drain coolant that gets by one or both seals as they begin to wear. If that is the source of the coolant leak, replacement of the seals is necessary, often requiring engine removal since the pump is driven off the camshaft. <br /><br />One other note, you mention having replaced the pump impeller. I assume you are referring to the impeller located in the outdrive (raw water pump), if not, check there for inadequate cooling. But since it's leaking, and you made mention of the front of the engine, I would head toward the closed system 'water' pump. If the head gasket were a problem you would encounter additional problems like water in the oil, extremely poor performance and stalling without capability of easy restart. Hope this helps.

 

[sbuckx]

Re: mercruiser coolant boiling

Thanks MrBill. Everything that you assumed I was saying about the outdrive impeller was correct. I never noticed the leak in front last season and suspect that this is the culprit. I already made an appointment with the local boat shop to look into this, because I was running out of options. They agree with you on the head gasket. Now I can point them in this direction, because I definitely don't want to get into removing the engine myself. I think it is lousy that it has to be removed, it looks like it is accessible without. I will take your word for it though. Looks like I will be forking of some $$$$.

 

[Trent]

Re: mercruiser coolant boiling

Take a look at this link....<br /><br /> Coolant Leak

 

[sbuckx]

Re: mercruiser coolant boiling

thanks for the link Trent. Yeah this is definitely beyond my expertise/patience/tools. I don't think there is enough clearance in the boat to leave the motor in. The boat shop is going to love me.<br /><br />Side note. I purchased the boat last spring and ran it all year like this. Makes me wonder if the guy I got it from knew about it, or if it started the spring that I bought it.