Mercruiser 3.7L Overheating and taking on water

[joburnet]

I bought a 1988 Baretta 18.5ft bowrider this winter and took it out for the first time today. It has the Mercruiser 3.7L 4 cylinder engine with about 165 HP and an I/O drive. After I fueled up I took it out and after 15-20 mins and noticed that there was a lot of water in the engine compartment, so much water that it was spraying all over the place from the serpentine belt. The engine was also very hot, water that would touch the top of coolant resiviour would instantly boil off. The temp gauge seemed to be working and was reading normally. I filled the engine up with coolant but it didn't seem like it was enough coolant to fill it up completely, I thought it would need more.

I turned on the bilge pump but that didn't seem to work at all, so that's my first order of business. I want to know how that water got in there, and why it was overheating. One thought was that whatever hose pulled water from outside the boat into the engine was loose or not there at all, that would explain both problems. The boat does have a cooling system so the internal coolant never touches the water outside the boat.

I'm not very familiar with boat engines yet, and I know nothing about I/O drives but I'm willing to learn. Any suggestions on where to start? Are there haynes manuals for these engines and drives?

 

[plassiter1]

Re: Mercruiser 3.7L Overheating and taking on water

maybe the heat exchanger

get it dry and examine all coolant hoses carefully

I have the same engine.

 

[joburnet]

Re: Mercruiser 3.7L Overheating and taking on water

I forgot to mention that it's been in storage for about 2 years after being winterized.

How exactly does a heat exchanger work?

Where is the water intake for this?

 

[88wellcraft]

Re: Mercruiser 3.7L Overheating and taking on water

Might sound dumb...but did you check the engine compartment before you put it in the water? Assuming you did...I would make sure you raw water intake is working properly and not leaking from anywhere. Get an infrared thermometer and make sure your gauge is working properly.

BUT, first things first, you're right...get the bilge pump working

 

[EricR]

Re: Mercruiser 3.7L Overheating and taking on water

A heat exchanger does exactly what its name implies, it exchanges heat. Just like a radiator in an automobile, except where a car circulates the hot coolant in one end of the radiator, air flows across it, and it cools the coolant and returns it to the engine.

Your 3.7 uses raw water supplied by the water pump in the outdrive to pump water up to the heat exchanger, where it ciculates through tubes that the jacket water (coolant or antifreeze, whatever you want to call it) flows around. Then it is returned to the engine.

The 3.7 was a good engine but had it's quirks. Developed by MerCruiser in the late 70's when the fuel crunch came and car makers downsized, Merc worried they would not be able to get the domestic V8 car engines and engineered their own. It did however use a Ford big block iron head from a 460cid engine. It is an aluminum block engine, hence why they were all what they call "fresh water cooled".

The jacket water pump (some call it a circulating pump) is driven off the end of the camshaft, and when the water pump goes bad you get coolant in the oil. The alternator windings are built into the harmonic balancer (the idea behind these two things was to eliminate vee belts and therefore maintanence)

The alt goes out it is really expensive unless you convert to a separate belt driven alternator for which there are kits availible.

Very torquey engine but known to be a bit of a shaker at low speeds.

Any Merc experts feel free to correct me on anything I said.

 

[Coors]

Re: Mercruiser 3.7L Overheating and taking on water

Fix the bilge pump; put it an muffs, open the engine compartment, and look , while it is running.
Pull out the plug, also.

 

[joburnet]

Re: Mercruiser 3.7L Overheating and taking on water

Thanks for the information, I talked to a mechanic who was worried it could be a cracked block but the engine oil still looks good, no water.

I noticed that it didn't like to idle for very long without stalling but did great at speed.

I'll fix the bilge pump, and then let it run to see where the water is coming in, should be pretty obvious because it was a lot of water. Where does the engine have the water intake and can I do this in my driveway rather then dragging it 30 mins to the nearest water?

 

[sea wolf]

Re: Mercruiser 3.7L Overheating and taking on water

The intake is on the lower unit. Get a pair of muffs {a must have for maintenance}, attach to a garden hose & fire it up. Also, get yourself a manuel for your setup, & familiarize yourself on how these systems work. Good luck. By the way, consider upgrading the bilge pump to a unit with more pumping capacity. Most OE pumps that boat manufacturers install are junk.

 

[joburnet]

Re: Mercruiser 3.7L Overheating and taking on water

Any suggestions for a quality brand and flow rate for a bilge pump?

 

[Chris1956]

Re: Mercruiser 3.7L Overheating and taking on water

Get at least a 500 GPH bilge pump. Any major brand is OK, as are the Marine Store Brands. I personally like the floatless automatic bilge pumps. They run for a few seconds every 3 minutes and if they detect water, they pump it out. keeeps the bilge pretty dry, much dryer than the internal or external float-switch type pumps.

 

[sea wolf]

Re: Mercruiser 3.7L Overheating and taking on water

Nah, 500 gph won't cut it. The flow rate will be reduced because the pump is pushing water uphill, so the 500 gph rating is baloney. I have a 1000 gph pump in my 19 ftr., plus a hand pump. Remember, the smaller the boat, the faster it can fill with water. A good bilge pump can save your hide, not to mention your boat.

 

[Coors]

Re: Mercruiser 3.7L Overheating and taking on water

I'm with Chris on the floatless; I installed a manual/auto switch, so I can turn it off when out of the water.