Merc 470 running hot

[2fishy4u]

I know this has been covered in a lot of ways. But I cant find anyone that has had a similar problem. I have a 28.5 searay with twin merc 3.7lx 180 4bbl

Starboard was running fine, always ran at 170. A couple months ago while heading out to the islands, the temp crept up to 200 before I stopped and shut it down. Verified temps with heat gun.
I have had multiple people look at and work on it. Here is what has been done, Replaced the exhaust manifold, riser, heat exchanger (4"), all hoses, exaust elbow, fresh water pump. And the head was replaced. Now, it runs at 180 temp up to 3k rpm with no load. It maintains its temp under load up to 2k rpm but anything over and it starts heating up. Checked fresh water flow and it has more than enough flow. Checked the closed cooling and it seams to flow ok. There are no leaks whatsoever, everything has been presure tested. There really is nothing left to the cooling except the water pump. But it does not seam it could go out. When we pull the hose and feel inside the blades seem to be intact, no odd wear is felt. ANd it is not loose that we can feel. I am literally 5k in and no progress. Could the water pump fail to the point it is not creating enough flow? Obviously to replace the pump is a mojor job, and I am not spending another 2k and still have this issue. At least I hope not.......

so are there any Merc 470 masters out there that has run into something like this??

 

[Eric 3.7LX Alpha 1]

Welcome to the 470 club! :thumb:

The engine circulating water pump almost never fails.

I run the same model and don't budge off 160? all day long with the 4" exchanger. My mind is thinking drive related.

Your port engine runs at what temp?

Did you do just the impeller in the drive or the whole kit including the base and upper housing?

How about a drive swap test? Either swap them over and see if the temp issue moves with it... or...

pull the water inlet hose "E" in the diagram (from the drive)... attached to the Voltage Regulator (if you still are have it) Couple it with another piece of hose and connect it to the voltage regulator of the other engine. 5/8" heater hose sold at auto parts stores fits perfect, along with a small section of 1/2" copper pipe and some hose clamps to make the connection. Should do the same thing for you as long as the hose doesn't get kinked at all.

 

[stonyloam]

You did not mention thermostat, but I am assuming you did that. It does not seen likely that the engine waterpump would fail. Actually changing out the impeller should be pretty easy. Just remove the hose and take. Off the waterpump cover (NOT the timing chain cover) and unbolt the impeller. May be a bolt with locktite on it or a stud that has left hand threads (note the arrow on the impeller). I think the 4 barrel engines have a oil cooler, maybe that is plugged and you are loosing some cooling capacity there.

 

[2fishy4u]

Thanks guys,

So the drive was completely rebuilt 30 hours prior to this. Replaced the impeller even though it was in perfect condition. We checked water flow at every point right out the back of boat. Its definitely circulating very good. I just got a call from the mechanic, he did a flow test of the closed system and said it was weak but flowing. He is convinced it is not the impeller also, but at the same time is clueless at this point. I am going to have to fire him as he keeps charging me for all this unnecessary work....with no progress. Is it really that easy to change stonyloam??? If it is I will choke that guy, as everything he has done was major work compared. Thermostat was first thing I checked. replaced twice, didn't make any difference. Even ran without thermostat with same results.
And Eric with what I said do you still think a swap would be something to try? Its in the water, with no trailer anymore. So I would have to do your alternative suggestion of hooking them with a hose. And How would that work, wouldn't the port have to be running to drive the impeller to circulate the water in the starboard? And wouldn't it overheat with the water going to starboard instead of port? Or are you saying to hook up the port to the starboard and the starboard to the port and run both?

 

[salty3rd]

I agree with the above, i had the same issue a few years back and the only way to narrow it down was to swap drives. And sure enough it was a missing part in the water pump that was missing. Now im the only one that changes my water pumps..

 

[stonyloam]

Yeah you could just get a length of hose and run a line from the port water cooled voltage regulator to the intake of the starboard exchanger and visa versa. A length of inexpensive hose should do it since it is only temporary. Yeah it is that easy https://www.mercruiserparts.com/Sho...39469.png&inbr=908&bnbr=170&bdesc=FRONT+COVER you only have to take off the impeller cover #15. You could see if one exchanger is getting hotter than the other. If the hotter engine has a hotter exchanger then you probably have a raw water flow problem, if the hotter engine has a cooler exchanger then you probably have a engine coolant flow problem. Anyway I think that would be how it works. I agree with Eric, there is not much that can go wrong with the engine water pump impeller. But you never know.

 

[Eric 3.7LX Alpha 1]

Well couple of things to check/try so far in this thread. With all of those new parts on the engine there really isn't much left it could be.

I like the idea on checking/comparing the temp of the heat exchangers to see if raw water flow or coolant flow issue. Great starting point there.

How long have you owned this boat?

To get at the impeller on the engine I'm pretty sure you will have to remove the rotor (harmonic balancer) first, it blocks one or two of the bolts on the impeller cover. You can rent a harmonic balancer puller/installer from Auto Zone for free. That will probably be the toughest part of the job, but it's not bad at all as long as the engine has room in front of it for the puller.

http://forums.iboats.com/forum/engi...oving-rotor-pully-covering-stator-on-merc-470

 

[stonyloam]

Yeah Eric you might be right there, the rotor might block a couple of the impeller cover bolts, but still it is not a huge job to remove the rotor. I think that I would save that job for the very last thing to try, because it is quite unlikely to be the problem.

 

[2fishy4u]

Thanks guys, I get the weekends to go to the boat. I will definitely try the drive swap and see what happens. Ran out of money, so I will be doing everything myself from this point. I have had it for 2 years Eric, I just re-powered the port after a piston rod broke..... Then this started first trip out. Then I guess try the impeller as the last resort. I've been told to sell it and start over, but I love the boat. And once this is sorted out, with proper care and maintenance these are good engines.

Ill let you guys know if I make any progress or still need advice.