Mercruiser 6.2L MPI overheating

[platon20]

Boat is freshwater, 2017 with 35 hours on engine; raw water cooled.

My engine temp goes from 60 to 200 within 60 seconds after starting the engine and leaving it at idle. It overheats both when connected to water hose as well as when on the water.

I checked the sterndrive water inlets for blockages/debris and it looks clear

The first thing I checked was the impeller, but I just put in a new one a few days ago and it looks fine to me (see pics). It's slightly difficult to turn on the pulley but there was no squealing of the belt while it was running and the pulley was definitely spinning when the engine was running so that should be OK I would think. I did notice when taking off the impeller housing that there was a very slow drip from the edge of the housing, but there was no water in the bilge to speak of.

I guess it's possible the old impeller had pieces come that are blocking something? When I took off the old impeller I didn't see any broken off pieces though.

Is there something in the sterndrive that is supposed to pump water up to the impeller?

My cooling flow diagram is attached, I see 5 possible areas to check:

1) water circulating pump (k);
2) fuel supply module water inlet strainer (f);
3) distribution housing (h);
4) crossover with thermostat - n
5) poppet valve assemly (q)

Which part should I check first?

 

[Scott Danforth]

overheating is from lack of cooling water flow

check the line from the pump to the pickup. including where it goes thru the gimbal. backflush as needed.

check your PS cooler and cool fuel module for plugged tubes.

check the poppet valve.

35 hours on a 4 year old boat is not many hours you should use it more often.

 

[QBhoy]

If it does that after starting from cold...I’d be almost certain it’s not genuinely doing that. Sure it’s not the famous SW pressure sensor needing replaced...common to these mpi.

 

[platon20]

I used an IR gun to check the temps, it's definitely overheating. However this time when I started the engine it took about 3-4 mins to get above 180.

When I shut off the engine at 190, the risers were reading 210 with the IR gun.

 

[tpenfield]

Did you replace the impeller (a few days ago) because it was overheating?

If not, did the engine ever cool properly after you replaced the impeller?

Things to consider/check. . .

Hoses connected backwards at the sea water pump.
Marine life clogging the coolant flow.

Are you getting any water to come out the exhaust/transom ports when you run on the muffs/garden hose?

 

[platon20]

Update: I disconneted the water inlet to the impeller and used a garden hose to push water thru and it worked like a champ, the highest temp the engine go up to was 152 F after 15 minutes. The thermostat is 140 F.

After that I ran the garden hose backwards into the hose that runs to the transom and there was some water coming out at the inlets on the sterndrive but it wasn't very much.

So apparently I have some kind of obstruction somewhere in the sterndrive up to the impeller inlet. I used an endoscopic camera to snake down into the hose connecting the impeller inlet to where it attaches at the transom and didn't see anything blocking it.

I looked closely at the water inlet holes on the sterndrive and there's no debris or blockage. It must be higher up somewhere

I guess the next step is to take off the stern drive? I thought about trying to disconnect the hose where it attaches at the transom to look at it but I can't really get to it

 

[alldodge]

Check the water hose going from the drive bell housing to the transom plate. It might be twisted and going flat

 

[kenny nunez]

It will be interesting to find out what is causing the blockage.

 

[platon20]

I have to wait for a stern drive holder to arrive and then I will take apart the drive and find out

 

[platon20]

I'm going to drain the gear lube first, I was going to drain it today and let it sit for 24 hours to drain everything out and then in a few days I will take it apart and look for blockages.

If I drain the gear lube and just leave it empty while I work on it, is that going to cause a problem with the air getting inside the sterndrive?

 

[Bt Doctur]

Might be Bravoitis, backflowing thru a Bravo you should have no resistance pushing water out the drives inlet holes

 

[Scott Danforth]

If I drain the gear lube and just leave it empty while I work on it, is that going to cause a problem with the air getting inside the sterndrive?

No, as long as you put the plug back in. i would also put a tag on it that there is no oil.

 

[platon20]

Might be Bravoitis, backflowing thru a Bravo you should have no resistance pushing water out the drives inlet holes

I thought about that, but my boat has only 35 hours on it and has never been on saltwater. Does Bravoitis happen that fast? I just wouldn't expect a lot of corrosion yet on this engine.

I'm thinking more likely it's some kind of mechanical blockage of the tube, something getting sucked up inside like a piece of plastic or something

 

[kenny nunez]

According to the consensus on the Donzi site the best thing to do with a Bravo is to add a pickup through the bottom with a sea chest and a valve. You can hook up the line from the drive with a “Y” connection which is also a suggestion in the Mercruiser service manual, that way you can still use the ear muffs to flush out the engine and the water circulating through the drive will keep it cool. Bravos have a habit of collecting debris even small sea shells.

 

[blamtro]

No, as long as you put the plug back in. i would also put a tag on it that there is no oil.

DO NOT do this. I had a drive I drained and due to a health issue/surgery didnt get back to filling up until the beginning of the next season. Some gear and bearing surfaces flash rusted.

the mercruiser spec gear lube has special water dispersants in it to help handle a higher percentage of contamination of water then a non marine lube and when drained, can leave moisture on your bearings/gears. If youre going to drain it, fill it back up. If not, leave lube in until you can drain and fill same day. Please learn from my expensive mistake.

 

[tpenfield]

There is that old saying . . . 'You can get a lot of exercise by jumping to conclusion.'

I agree that the boat/engine is quite new to have Bravoitis. Typically you'd be looking at 10-15 years of age. However, you seem to have isolated the issue as being between the outdrive lower unit inlets and the sea water pump. So, it is time to get busy and start eliminating those possibilities, which can be many.

Have you removed the outdrive and inspected the water duct, the fitting at the bell housing, the transfer tube, and then anything else that lies between the outdrive and the sea water pump?

 

[platon20]

DO NOT do this. I had a drive I drained and due to a health issue/surgery didnt get back to filling up until the beginning of the next season. Some gear and bearing surfaces flash rusted.

the mercruiser spec gear lube has special water dispersants in it to help handle a higher percentage of contamination of water then a non marine lube and when drained, can leave moisture on your bearings/gears. If youre going to drain it, fill it back up. If not, leave lube in until you can drain and fill same day. Please learn from my expensive mistake.

My boat is in the garage so no water will be getting in there.

 

[platon20]

There is that old saying . . . 'You can get a lot of exercise by jumping to conclusion.'

I agree that the boat/engine is quite new to have Bravoitis. Typically you'd be looking at 10-15 years of age. However, you seem to have isolated the issue as being between the outdrive lower unit inlets and the sea water pump. So, it is time to get busy and start eliminating those possibilities, which can be many.

Have you removed the outdrive and inspected the water duct, the fitting at the bell housing, the transfer tube, and then anything else that lies between the outdrive and the sea water pump?

I will be checking those things in a couple of days, I'm waiting for my sterndrive trolley to arrive.

 

[platon20]

Update: successfully removed the sterndrive, however 2 screws holding the trim sender to the bell housing are stripped, so I'm waiting to get a screw removal tool to help get them out.

In the meantime I was looking at my shift cable clasp in the upper unit and it's very loose and flimsy. Is it broken, or is it supposed to be loose like that? The 2 clasps just fall together instead of "latching" tight

I never had any problems with shifting while the boat was running so I assumed it was OK but wanted to double check.

 

[alldodge]

The top piece just flaps, it will stay in place once drive is on because there is no room for the clasp to raise enough to cause the cable to come loose