Mercruiser 5.7 MPI Cooling System Won't Exhaust Water

[Skelley]

I fired up our 2002 Cobalt 246 boat after storage today on ear muffs and it runs fine, but temp started going over 170 and I noticed very little water was coming out the B3 out drive exhaust port. Ran perfect last season. Last fall when winterizing I put a new impeller in the sea pump (2nd time I've done this and the pump turned fine after reassembly with Vaseline to lube it). I also cracked the thermostat housing after draining all water and filled with a gallon of anti freeze. Cleaned up stat housing and resealed last week. Upon startup, I waited for water to start coming out the stat housing drain before I added the pet clock to prevent air from being trapped. All normal process as I've done for 5 years. I let cool down and drained the water - dirty looking and probably much of the anti-freeze. T-stat was replaced two yrs ago. I only use Mercruiser branded parts. Engine has 550 hours. Any ideas why very little to no water exits the out drive?

 

[tpenfield]

One idea would be the water passages in the exhaust manifolds or elbows are becoming clogged up. Have you checked those recently?

 

[Skelley]

Thanks, Ted. No, I haven't. I fired it back up this morning on the ear muffs, water in engine drained. No water coming out of the T-stat housing drain port after running 30 or so seconds so I shut it down. Water ran out of the t-stat housing drain shortly after fire up yesterday. Pulled the drain plug out of the lower water unit and almost nothing came out. I pulled the engine drive belt and the sea pump turns and feels normal. Seems like some is preventing water from getting to the sea pump perhaps. New impeller last fall. How could it be pumping water yesterday and none today? Baffled.

 

[alldodge]

Howdy Skelley

Look at your hose connections to the seawater pump housing. You have a left handed rotating motor and the suction hose needs to be on the correct side of the pump. My Rinker uses V belts the suction hose is on the top. My Formula uses a serpentine belt and the suction line goes on the bottom. Same pump housing for both motors but the routing of the belt makes the difference. Yours may be different

 

[tpenfield]

Also, there is (or should be) an oil cooler in line between the seawater pump and the T-stat. If the oil cooler get clogged, then you will get little/no water flow through the engine. you can back flush the oil cooler by sending water down from the hose that connects to the t-stat housing and at the same time disconnect the output hose at the se water pump.

 

[Skelley]

Great suggestion, Ted. Much appreciated. I'm still a little confused if I have the hoses on the sea pump installed the wrong way as it clearly brought enough water into the engine yesterday when I first started it up. It poured out the t-stat housing and when I drained it, I had much more than the 1 gal of anti-freeze I put in last fall. So if the hoses were wrongly installed, I'd think there couldn't be any suction at all to pull water in. Hmm. I'll check both the hose to the pump and the oil cooler as you've suggested on Thursday when I'm free again. Much thanks to both of you for the suggestions!

Here's my cooling system routing from Mercrusier... Looks like suction hose should be on top of sea pump. Is item 23 at the back of the engine the oil pump cooler? Mercruiserparts says it's a brass tube. I also have a fuel cooler that it looks like water from the sea pump runs through. Thanks much for your help and suggestions.

 

[alldodge]

The water that came out the thermostat housing when you first fired it up could be what you had in the engine block. The circulating pump would move it around very quickly. Now if you took the hose off the housing that was coming from the seawater pump, and it came out when you fired it up, then its in correctly.

Also item 13 is a check valve, should not get stuck but it can happen

 

[Skelley]

So the fresh water inlet hose was correctly connected to the upper connection on the sea pump. They are molded hoses and would be difficult to reverse. I called Mercruiser tech service and shared what I had done and your suggestions. I was advised to disconnect the water inlet hose at the transom and try feeding the garden hose to the sea pump to see if I had any blockages. Everything was great with normal water flow out the exhaust. Ran for 15 min and temp stayed in normal range. Then hooked hose back to fitting and hooked up ear muffs - no water coming out. I then disconnected the water manifold at the transom, sure enough, what many in the repair business call I've learned, Bravoitis! The hose and expander plug have collapsed due to corrosion build up. I can't even get any small finger in. Further search on I boats forums, I've learned about a good fix from Aftermarket Marine. They have a stainless fixture and formed hose that eliminates the corrosion potential. I'm planning to have this installed. Anyone familiar or has had this added to their boat? http://www.amarket.com/BRAVOblock.ham

 

[alldodge]

I've seen them but don't know of anyone that has actually installed one. If you do it take pics and post

 

[Skelley]

Ok, been a while and still playing with this issue. Making progress but now runs 175+. Since last shared, my initial concern was lack of water flow out of exhaust at the bottom of the gimbal housing area. I put in the new molded hose at the transom through the gimbal housing using the aftermarket unit with stainless fitting at transom. It is not kinked either while out drive goes up/down. In fact, I have verified water flows very well out of sea pump by pulling hose at feed side of p/s cooler. It also flows well at top of exhaust elbows when I pull these while running. Verified both on garden hose and in lake. Pretty convinced no blockage through coolers. Also removed the water distribution manifold below the front of the engine to verify not plugged or corroded, fine. Removed from boat and blew water through most external hoses - to/from sea pump, from T-stat housing to bottom of both exhaust manifolds, from manifold under engine to bottom of exhaust manifolds where they push water up to the ball in the fitting. All good and clean. Then, I replaced the T-stat. Only 3 yrs old. Put both new and old in pot on stove. New one opens a bit sooner and opens more than old one, but old one certainly opened. Thought that was it. Then I decided to replace the exhaust manifolds and elbows. They were reported new when I bought the boat 7 yrs ago and were cheap aftermarket brand. Keep in mind, boat was used in brackish water for 7 yrs prior, but only fresh water since I've owned. New everything, gaskets, hose and ball fitting at bottom of manifolds and fasteners. Also new exhaust shutter valves as they were totally burned up. Water now flows through manifolds and out the exhaust at gimbal housing. Elbows cool to touch - again on ear muffs. Thought everything was fixed!

Took boat 4 hours to lake for this weekend. First 1/2 mile is no wake, so idling and temp goes to 175 and a little higher. Got up on plane and cooled off to about 170 for a bit, then went over 175. Sitting in lake, both elbows are quite hot to touch. Stat housing very hot to touch. What's going on??? Got boat back to rented slip while maintaining 175 and let sit over night. Fired up this morning and rechecked water flowing well at p/s cooler inlet and feed to both exhaust elbows.

Thinking now might not be generating enough water flow throug engine recirculating pump. Removed engine drive belt and pump turns very easily in both directions. Surprisingly easy. No thumping or noise as if bearing went out. Weep hole is dirty looking, no evidence of seeping water. Was able to stick pointed end of a zip tie about 1.5 inches into weep hole. All is dry around pump. Pump looks original to me. Paint over bolts and stud threads. Can the vanes in the pump corrode over 14 years and 565 hours so they no longer pump the required volume? Going to look for a recirculating pump today. With what I've spent already, another hundred or so is small to rule this item out. Most parts used are Mercruiser brand. Barr Marine manifolds and elbows. I'm very conscious of my work and cleanliness. Torqued all manifold fasteners, etc. This problem is getting the best of my 40+ years working on vehicles and engines! Any ideas?


Thanks,
Steve Kelley

 

[Skelley]

Oh, forgot to add I put another impeller in the sea pump as I thought I may have run it dry with no water coming out of gimbal housing. It was fine. Housing is clean without any wear marks. I've also never seen any chunks of impeller missing upon every other year maintainence replacement.

 

[alldodge]

You said the exhaust and thermostat housing is hot, the only way for both of them to get hot as I see it, is if the seawater pump is not pumping. If the engine circulating pump is not working or has a broken vane, the motor gets hot but the exhaust stay cool.

I suggest removing and bypass the check valve item 13.

 

[Skelley]

Thank you very much! I see you suggested this earlier and I've not done this. Makes sense if it's getting stuck. The intermittent nature of hot and cool exhaust elbows has been confusing.

 

[Skelley]

No Title

Well, the one way check valve was an issue. Found two pieces of a very old impeller stuck in it. In my 7 yrs of ownership and three impeller replacements, never any broken blades. By the cracks and rust stains on the chunks, there is no way this is the impeller I put in a few weeks ago. The valve works fine now. I couldn't find a replacement valve today (and now don't need it) so I started it up with a bypass piece of 1" PVC. Ran fine and came up to temp normally. Exhaust elbows stayed cool. Saw temp gauge go up to 175, then back to around where 170 or so would be, acting like it did last year. After another minute, it started going over 175. Finally alarm went off and I shut it down. Exhaust elbows still cool. I'm planning to take home, back flush both coolers individually, remove big hose to stat housing and housing once again to check for pieces. I'll take apart the sea pump once more just to verify all blades are intact. Then plan to remove recirculating pump to check it out. Looking for more pieces of the old impeller. Any other thoughts?

 

[alldodge]

With exhaust staying cool now, I would lean toward the circulating water pump. The motor is getting water something is just not getting cool water into the block. So if the thermostat is installed correctly (including sleeve item 6), its about the only item left.