Mercruiser 3.0L w/heat exchanger Overheating?

[tule1]

I have a 2001 Bayliner with 3.0l Mercruiser. It has an aftermarket Seakamp heat exchanger. The boat ran flawlessly until last summer when it would start to overheat when I’d slow down to no wake speed or throw it in neutral. The temperature will continue to rise until I either idle up to a couple thousand rpm or get her up on plane real quick and then the temp will drop right down to 160 degrees. The boat doesn’t overheat at speed, just when I’m idling into harbor or have to drive real slow. Other than the overheating it runs flawlessly.<br />I have put a new impeller in it, the one that was replaced was in perfect condition. I have also put a new circulation pump on the engine to circulate the freshwater side of the system. I’ve pulled the exchanger to see if it was clogged and there are no obstructions or corrosion inside. I’m stumped!<br />I have felt the exhaust elbow to see if it's getting hot thinking it might be clogged but it stays cool to the touch.<br />Anyone have any suggestions for me before I take it in to a shop?<br />I would appreciate any help offered here.<br /><br />Thanks, Dave

 

[Haut Medoc]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

How old is the heat exchanger?

 

[Haut Medoc]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

I had exactly the opposite. Mine would over-heat @ high RPM, cool down @ idle. Over -heating is generally either circulation or restriction. Since the exaust riser stays cool i would tend to think that the problem is not on the sea water side.The problem with mine was the freshwater side of the exchanger was clogged internally, and that's the part you can't see. Was this converted from a raw water cooled engine?......

 

[tule1]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

The heat exchanger is about 4 years old. I pulled it off last year when I started having this problem and it was clean inside.<br />This boat was converted from raw water cooling.

 

[Haut Medoc]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

What I mean to say is you can't see inside the closed side of the exchanger. When you pull the side caps and look through, that is the raw water side of the system. That this problem came on gradually suggests that loose scale from the days when it was raw water cooled are slowly clogging the exchanger. Espiecially if it was run in the Sound. If there is any way for you to borrow an exchanger that is known to be good, I would try that. If you can't, Second Wave in Fremont might have one. I suppose the T-stat. might have something to do with it , but I really doubt it. I really think it's the exchanger, hopefully you'll get some more input.........J

 

[tommays]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

your manifold and riser are staying cool so you have enough water flow<br /><br />the t-stat would be the next easy thing to check<br /><br />takeing the exchanger to a raditor shop an haveing it cleaned out would be a low cost way to cross it off the list<br /><br />tommays

 

[tule1]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

I put in a new thermostat AND tested the old one in a pot of water on the stove and the old one was fine.<br />I've field tested it with the engine cover off just to see what's going on. When I slow down to an idle, which is when it will start to heat up, I can see the coolant pushing out of the engine into the overflow tube and back into the coolant overflow reservoir. Sounds complicated but in simple terms, as my engine heats up it starts pushing the coolant out. I talked to a marine tech and to him it sounded like maybe my head gasket is bad causing gases to build up and push the coolant out. I'm not too sure about that but he said the first thing he'd probably do a check on would be my head gasket.<br />Thanks for the responses, I'm still stumped.

 

[tommays]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

well that is actually possable as i have had it happen on two cars the overflow would bubble like a coffe pot<br /><br />i think you can get a test strip that will check for exaust stuff in the coolant if not a car type raditor pressure tester is not to much money <br /><br />tommays

 

[Bondo]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

If it was the Headgasket,... It would Overheat All the time,... Especially at High RPMs.....<br /><br />I think I'd Flush the raw water side.....<br />Have you Checked for Flow ??? Pull the hose coming from the drive,+ See if it's Moving Good Water Flow........

 

[tule1]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

Bondo, when you say pull the hose coming from the drive are you talking about the hose from the outdrive to the exchanger?<br />Are the riser and elbow the same thing?

 

[Haut Medoc]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

Yes

 

[tommays]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

my first guess is the heat exc and if i had never owned a VW i would say no way on the head gasket but it happened to allmost ever early one they made<br /><br />strangest thing you ever saw pushed it out and sucked it right back in and hardly lost a drop <br /><br />www vanagon com/problems/head-leaks.html<br /><br />This is usually noticed when the overflow tank suddenly fills up with a hot engine, and draws back in while cooling. This leak is less common than the first, and gives longer warning time.<br /><br />tommays

 

[tule1]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

Thanks for the responses. I'm going to install a new manifold and riser to see if that solves the problem.<br />The manifold that is used is both an intake and exhaust manifold. I noticed that my manifold gets extremely hot toward the front(where the raw water enters) and is cooler toward the back of the manifold(where it enters the elbow and exits). The middle of the manifold is where the carburetor sits and it is hot on one side and semi-cool on the other. Is that telling me that there might be blockage in the manifold somewhere?

 

[tommays]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=011013 <br /><br />have a look a these i just pulled mine to check the water passages this weekend <br /><br />2 bolts and a 2.50 gasket to check<br /><br />if there cloged were the riser bolts onto the maifold thats a good sign there getting old<br /><br />you never have said how hot you getting? usally when there cloged you would get hot at high speed<br /><br />tommays

 

[tule1]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

The temperature will rise until it's pegged on my gauge if I let it. When it starts to climb past 180 or so I either get it up on plane or put it in neutral and idle up to 2500 rpm which brings the temp down.<br />I'm replacing both the manifold and riser but still have concerns about the head gasket or maybe some warping.<br />Thanks for the replies.

 

[xltier]

Re: Mercruiser 3.0L w/heat exchanger Overheating?

ive been a mechanic for 30 years and have never seen a head gasket that was worse going slow than it was going hard.just my observation![or 2 cents}