Maxum 2700 SCR Mercruiser Strange Leak - Maxum Boat Owners Club

Pilotrob25 · 03-24-2015, 02:49 AM

Okay so I want to give the full story on this as we are all confused!

2000 Maxum 2700 with a Mercruiser 350 (Carb) went into the shop and I had new manifolds and risers installed along with a new transom assembly, oil change etc. Ran the boat about 2 or 3 hours after. No problems noticed. Took the boat out New Years Eve and did a lot of idling. Once back in the slip we noticed a oily sheen behind the boat. Not sure if its oil, power steering, coolant, drive oil or gas. Also noticed a thin white smoke or steam. Smelled like an outboard motor is the best way to put it. (I assumed oil burning) Few weeks later I took the boat on about a 3-4 hour cruise and noticed the water temp gauge was not getting above around 120-130. So running cold. 175 is Normal. (Stuck thermostat?) Got back in the slip and decided to top off all fluids and see which is leaking. Since then I have noticed the oily sheen no longer appears and no smoke or steam either. Awesome right. Wrong, pulled the coolant cap off today and its missing a lot of coolant. No coolant in the bilge or anywhere visible. I have the half system so the manifolds are raw water. Engine runs just fine with no noticeable loss of power. I did notice my cruise speed was down 1 or 2 mph but that can be a lot of environmental things. So in conclusion, leaking coolant, low temp and a magically fixed oil out exhaust issue. Who wants to take the first crack at this?? haha

mmwjr · 03-24-2015, 02:58 AM

Me oh me

Half closed system so just the engine.

Coolant was low, was oil level normal or high?

Since transom Assy was replaced the engine was pulled, correct.

I suspect coolant is being burned and going out the exhaust so this means either a leaking head gasket or intake.

Stuck t-stat would result in overheat. Since the closed system is leaking the coolant is probably not touching the senior and the reading will be off.

Pull the spark plugs and see if any are wet.

mmwjr · 03-24-2015, 03:08 AM

BTY burning oil shows up as blue smoke, to rich on gas will be a black cloud, and water being burned is white.

Pilotrob25 · 03-24-2015, 03:34 AM

I haven't pulled the plugs yet but with the engine running as well as it does I don't expect to find much. My thinking is that its leaking into the manifold. I put stop leak coolant in it and the sheen behind the boat no longer appears. It was very noticeable on start up. So here is my conclusion so far. Coolant starts leaking into manifold. When the engine stops the leak continues until the pressure drops. When I start the boat the coolant that pooled up gets pushed through creating the sheen. The thermostat stays in the open position due to low coolant flow on one side. (One side is running hot) Now that the leak is under control from the "Stop Leak" it had to fill the empty space in the block with coolant so thats why it dropped so fast in the exchanger. This is my best guess so far today.........

Pilotrob25 · 03-24-2015, 03:37 AM

Quote:

Originally Posted by mmwjr

Me oh me

Half closed system so just the engine. CORRECT

Coolant was low, was oil level normal or high? NORMAL, ACTUALLY USUALLY HAVE TO ADD OIL

Since transom Assy was replaced the engine was pulled, correct. YES

I suspect coolant is being burned and going out the exhaust so this means either a leaking head gasket or intake. THATS WHAT IM THINKING, BUT A BAD HEAD GASKET WOULD CREATE A ROUGH ENGINE AND LOW OIL PRESSURE RIGHT?

Stuck t-stat would result in overheat. Since the closed system is leaking the coolant is probably not touching the senior and the reading will be off. NOT IF ITS STUCK OPEN. NO OVERHEAT ALARMS.

Pull the spark plugs and see if any are wet.

Half closed system so just the engine. CORRECT

Coolant was low, was oil level normal or high? NORMAL, ACTUALLY USUALLY HAVE TO ADD OIL

Since transom Assy was replaced the engine was pulled, correct. YES

I suspect coolant is being burned and going out the exhaust so this means either a leaking head gasket or intake. THATS WHAT IM THINKING, BUT A BAD HEAD GASKET WOULD CREATE A ROUGH ENGINE AND LOW OIL PRESSURE RIGHT?

Stuck t-stat would result in overheat. Since the closed system is leaking the coolant is probably not touching the senior and the reading will be off. NOT IF ITS STUCK OPEN. NO OVERHEAT ALARMS.

Pilotrob25 · 03-24-2015, 04:56 AM

Video I took when the leak was visible out the back. You can see the thin white smoke and the oil/coolant coming out of the water

https://www.youtube.com/watch?v=M1qFBbFJFgc

Pilotrob25 · 03-24-2015, 04:58 AM

Video I took when the leak was visible out the back. You can see the thin white smoke and the oil/coolant coming out of the water

https://www.youtube.com/watch?v=M1qFBbFJFgc

mmwjr · 03-24-2015, 12:48 PM

Quote:

Originally Posted by Pilotrob25

Half closed system so just the engine. CORRECT

Coolant was low, was oil level normal or high? NORMAL, ACTUALLY USUALLY HAVE TO ADD OIL

Since transom Assy was replaced the engine was pulled, correct. YES

I suspect coolant is being burned and going out the exhaust so this means either a leaking head gasket or intake. THATS WHAT IM THINKING, BUT A BAD HEAD GASKET WOULD CREATE A ROUGH ENGINE AND LOW OIL PRESSURE RIGHT?

Stuck t-stat would result in overheat. Since the closed system is leaking the coolant is probably not touching the senior and the reading will be off. NOT IF ITS STUCK OPEN. NO OVERHEAT ALARMS.

How many hours are on the engine?
If you are needing to add oil where is it going, leaking, burning, ...?

I have seen engines that have lost a cylinder and the owner did not even know. A bad head gasket will only cause a low of oil if it is near a return passage but will not result in low pressure.

Yes the t-stat could fail open, that and or low coolant will prevent an overheat warning however the engine could still be overheating. The temp sender must be in contact with the coolant to get an accurate reading.

Pilotrob25 · 03-24-2015, 08:19 PM

Quote:

Originally Posted by mmwjr

How many hours are on the engine?
If you are needing to add oil where is it going, leaking, burning, ...?

I have seen engines that have lost a cylinder and the owner did not even know. A bad head gasket will only cause a low of oil if it is near a return passage but will not result in low pressure.

Yes the t-stat could fail open, that and or low coolant will prevent an overheat warning however the engine could still be overheating. The temp sender must be in contact with the coolant to get an accurate reading.

Maybe 350 hours on the engine. No idea where the oil is going. Most likely just burning it. I don't belive the engine is overheating. Ran it at 4000 rpms for hours. My guess would be that the engine would be toast by now if it was overheating haha

mmwjr · 03-25-2015, 02:02 AM

An engine with 350 hours should not be burning any oil.

Check the spark plugs and do a compression test.

Pilotrob25 · 03-25-2015, 04:48 AM

Bought the boat 6 months ago and compression was good. There was a small oil leak that we thought we fixed but there is still a small amount of oil in the bilge. 1 plug during the inspection looked like crap but didn't seem to bother the mechanic. I did a compression test on the cooling system today. Pumped the cooling system up to 15psi and it instantly started dropping maybe 1psi every 5 seconds. So now we know there is at least some leak. Starting to think the oil sheen and the coolant are 2 different issues. Note that the oil sheen/smoke are no longer present. Fired the boat up with little effort. Stalled the first time on startup but that seemed more like a normal carb boat type start. Fired right up the second time so I'm thinking coolant is not getting in the combustion chamber. No smoke either. So I'm going to pull the heat exchanger and take it down to a radiator shop to check for leaks. Anybody know how to drain the thing before I pull it off?

mmwjr · 03-25-2015, 12:43 PM

Are you seeing any signs of anti-freeze around the HE when you pressure tested it? Still could be a closed to raw water leak in the HE. Other than that it's a few hoses and the engine.

Best of luck.

Pilotrob25 · 04-03-2015, 09:48 AM

SOLVED! Okay so here is the fix. After pressure testing the coolant system we had 2 leaks. One was from a hose on top of the heat exchanger, hissed like crazy. Hard to miss. The 2nd leak was the reason for the low water temp readings. The hose just above the water temp gauge was leaking....right onto the sensor! The sensor was covered in glycol! I replaced the temp and overheat sensors and 4ft of hose and good to go!

mmwjr · 04-04-2015, 12:34 AM

Glad to hear you resolve the problem.