Mercruiser cooling issue

[Scarborough]

Hi,
I have a Mercruiser 2001 5L MPI, raw water cooling and with about 800 hours on it,
We have been out for the day and all seemed to work fine, except for the engine temp gauge was not showing any temp at all and we didn't get any hot water to shower in. Only reason why I didn't turn back was because I also have a Northstar GPS with Smartcraft installed and it told me the engine temp was fine, no overheating alarm either. What I did notice during the trip was that the temp gauge momentarily came back and at the same time Smart Craft indicated the water pressure increased from about 10 to 15/18psi then back again to about 10 when temp gauge showed no reading.

When we got back I pulled out the boat and flushed the engine as usual but this time the overheating alarm sounded and I turned it off. Note that Seawater pump and circulation pump has both been recently replaced (Seawater pump because the impeller broke and the housing was in bad nick). During the flushing of the engine the water is come out equally no problem from both sides.

I assumed that it was the thermostat which I changed but I still have the same problem. Can I just have been unlucky and bought a faulty one (bought it from a Mercruiser dealer and it was a stainless steel one)?

3 questions:
1 ? Why is it overheating during flushing but not running (the water supply has always been enough before to flush it)?
2 ? Any idea on why we first lost engine temp gauge and hot water?
2 ? Where does the Smartcraft temp sensor sit?

Cheers,
Scarborough

 

[Scarborough]

Re: Mercruiser cooling issue

To add to this saga.
I took out the new thermostat and put it in water that I hotted up to see when it opened, it open when it should so it can't be the thermostat. Next I back-flushed the hot water systems that takes the heat from right next to the thermostat and puts it back in at the circulation pump, no issues here either. I noted something interesting during testing it and that is she overheats if I just let it idle 600rpm (water 2psi) but if I rev up to about 1000rpm (2.7psi) then the smart craft temp Immediately goes down but stays in the 160-170, the other temp gauge falls back to nothing. Slow back down to 600rpm, goes hot again?

HELP

 

[Lyle29464]

Re: Mercruiser cooling issue

did you find 100% of the old impeller?

 

[Scarborough]

Re: Mercruiser cooling issue

Hi, I am not sure but the mechanic who did it said he though he did. I have tried to flush it as much as possible and I have seen any more impeller parts come out. When I flushed the hoses from the thermostat to the manifolds I could see water rising in the block where the water goes into the thermostat, is that right. Looking a link below it looks like there is a ball there to block the flow back?

http://www.boats.net/parts/search/Merc2/Mercruiser/5.0L%20MPI%20ALPHA-BRAVO/0M300000%20THRU%200M599999/Exhaust%20Manifold%20And%20Elbow/parts.html

 

[cr2k]

Re: Mercruiser cooling issue

First place to look is the in side of the heat exchanger.

 

[Scarborough]

Re: Mercruiser cooling issue

Unfortunately I don't a fresh water cooled system on this boat Or do you mean that I should check the risers and manifolds?

 

[cr2k]

Re: Mercruiser cooling issue

No I mean you should check the PS heat exchanger usually on the port side lower part of the block it is in line with the water line from the transom.

 

[Scarborough]

Re: Mercruiser cooling issue

Hi again,
Sorry have been away and just managed to get down to the boat and check it. I took the Power Steering Cooler off after a bit of hassle getting the one and only bolt off that holds it, it looks fine and the water goes through it ok. As I see it there are now only three places where the water splits left to check,
1 ? The Water Distribution Housing
2 ? The Lower Distribution
3 ? The join under the manifold from the thermostat and the lower distribution unit

Then I will take off the risers to check..

 

[Scarborough]

Re: Mercruiser cooling issue

Hi all,
A couple of things to add to the saga. Checked the water distribution housing and lower, nothing. I also back flushed from thermostat and circulation pump, all good.

Here is the new discovery. I started the engine and let her run until warm. The temp kept climbing, I went and felt the water coming out in the back, it was not hot even though temp gauge said 185. I then revved it a couple of times, temp went down and I run back and felt the water it was now very hot.

I am guessing that something has clogged the manifolds where the exit hot water from the thermostat goes into the manifolds and out, sounds about right?

Any suggestions?

Can someone tell me why there is a return to the lower water distribution unit connected at the same point as the exit hot water from the thermostat, if it come there it is hot and needs to be sent out, right?

Cheers

 

[Scarborough]

Re: Mercruiser cooling issue

Hi again,
I pulled off the manifolds and risers. The risers were in very bad nick. The manifolds do look like they are in pretty good shape. I opened all the plugs to clean it out and wow, it needed that. I have ordered new risers but I am not sure if I'll need new manifolds. Here in Australia they are about $380AU each (not Mercruiser) = about $400US so I am thinking I'll put it all back and test it and if the issue is still there then replace them.

Another day not boating

 

[Scarborough]

Re: Mercruiser cooling issue

Hi all,
Just in case some one else has a similar problem to what I had. I pulled every hose off, back flushed the engine and all parts, all good. I also pulled off the "new" water circulation pump just so I could back flush everything. Once I got it off it made a weird "clunk", I opened it up and the steel impeller was split in half. I also found a small piece from the rubber impeller jammed in there.

I have now got new risers and everything is working just fine .

Cheers,
Mats

 

[achris]

Re: Mercruiser cooling issue

...I opened it up and the steel impeller was split in half....

Sack the mechanic! Steel impeller means AUTOMOTIVE water pump, NOT marine. Marine pumps have cast brass impellers. In AU an automotive pump is less than $100, but a genuine MARINE one from Merc is over $650!

What part of AU are you in? Is your screen name your suburb? I ask because there is a suburb by that name in my city.

If you are in that suburb I would LOVE to know who your mechanic is.....

Chris..........
(Bibra Lake)

 

[Scarborough]

Re: Mercruiser cooling issue

Hi Chris,
Sorry for the late response but yes you are right, I scratch the surface and it was a cast brass impeller. I am just north of Brisbane. I got the water pump for $150 from http://www.suburbanimports.com.au/marine.htm guys in Sydney.

Engine is now running perfect at 160-163 at any speed, happy days again, until next thing lol