Mercruiser 350 Riser Overheating

[intrepidvoyager]

Re: Mercruiser 350 Riser Overheating

OK ...if I get this right ...... on muffs little water coming out of exhaust .... in the water lots of water coming out ...... seems to me you got lousy hose pressure to muffs or some muff issue. there is always less system water on muffs but sounds like you have really low pressure.

so you can't measure water volume out on the hard ...it won't mean anything .

If my boat ....and sounds like you have done a super job to check everything I would put the boat in the water everything hooked up ...BUT FIRST check there is no blockage in the exhaust Y or transom shield relief holes.

as soon as the engine is idling make sure you can squeeze the hoses going to the manifolds and that they are not hard.

wait for the thermo to open ...you should be able to feel this as the bypass water in the hoses to the manifold will go from cold to around 110 degrees.

As per the previous post re riser temp ..... you should be able to keep you hand on the riser ...140 degrees.. some people are more sensative and this does not work
so an IR thermo would help

up to 150 degrees at the riser is OK but if you start getting over 160 ...well in most boats with ok risers/manifolds it would be time for a new impeller.

I'll be interested to hear how it goes ..

 

[dlkb1240]

Re: Mercruiser 350 Riser Overheating

I have never run it with bunny ears/ ear muffs. My engine is a stern drive. I think of it as a half inboard/half outboard where the engine is actually in an engine room and the "lower gear unit" is out side of the boat. Sorry if I haven't been clear on this. I don't even have the lower gear unit on it yet. I'm trying to fix the main engine part first.

So I ran it yesterday but could only do it for a little bit. It appears while I was cleaning out the water system I stripped the threading on one of the bolts that holds the thermostat housing to the engine block so water was shooting out of that...no problem just get a new bolt but I didn't have one on hand. I got to run it for about 10-15 seconds. I had two 5 gal. buckets catching the discharge and I think it got somewhere between 1 - 2 gallons on each side. Another good sign. On the starboard side manifold there is some smoke coming from the exhaust port towards the bow. I'm thinking a bad manifold gasket... Again no problem those are relatively cheap.

I had a IR thermometer and the risers stayed at about 85-90 deg. The manifolds were around 110 - 120. Not sure if thats normal.

So my plan now is to fix all the problems I caused by taking the engine apart and then get it running for more than 10-15 seconds and take some temp readings,

 

[intrepidvoyager]

Re: Mercruiser 350 Riser Overheating

OK ......all sounds good .......110 at the manifolds is perfect ..... also sounds like you got lots of flow for operating off a hose ...... there is not much more you can do till you get the outdrive on and the boat in the water .... keep in mind that your raw water pump is capable of pumping up to 18gmp thru the system ...... unlikely you have that kind of flow from a garden hose so measuring the outflow on a hose is not going to mean much. Looks really good anyway from the short test you've done.

Also .......are you sure smoke from the exhaust manifold is not oil or some type of lub spilt on the engine ..... some people spray fogging oil all over the place when storing an engine so on start up the stuff burns off.....lots of smoke !!!

 

[intrepidvoyager]

Re: Mercruiser 350 Riser Overheating

one other point ...because you are running on garden hose pressure which has an average flow rate of 5 GPM you cannot match the approx 18 GPM flow rate of your raw water pump for which your cooling system is designed and therefore any temp readings you take will be high and will not reflect the actual operational condition of the system ....... in short ...you gotta get the leg on any the boat in the water.

 

[dlkb1240]

Re: Mercruiser 350 Riser Overheating

The boat is in the water. I have never run it with bunny ears or on garden hoes pressure.

 

[FreeBeeTony]

Re: Mercruiser 350 Riser Overheating

How are you running the engine with the boat in the water without the outdrive installed?

 

[intrepidvoyager]

Re: Mercruiser 350 Riser Overheating

You got to get the outdrive together and then test it .... there are issues dealing with exhaust gas back pressure with the outdrive not connected that will effect riser temps and give you false temp readings.

ON YOUR TEST You got about 4 gallons flow out in 15 secs ....... thats 16 gpm .....THAT'S RIGHT ON THE MONEY ....... FANTASTIC !!!!!

So get the leg together and let us know .....don't forget to check the rest of the exhaust ....Y tube,etc for blockage ...but looks like you have done that .

 

[SuperNova]

Re: Mercruiser 350 Riser Overheating

How are you running the engine with the boat in the water without the outdrive installed?

Uh, yeah, this has me curious also. You said the boat is in the water and you also said there is no lower unit on it. Do you have an engine driven raw water pump that pulls through a thru-hull fitting?

 

[dlkb1240]

Re: Mercruiser 350 Riser Overheating

Yes. The water comes through a separate intake. The outdrive part is just a housing for the gears to the prop.

SO i got her all back together. And ran her for about 7 minutes because water was shooting out of the thermostat housing. However, the temp readings were pretty normal the risers hit about 160 and stayed steady there. Good sign. (Side Note: I heated up the thermostat and it started opening around 130)

So i tightened up the thermostat housing bolts and ran it for about 10 minutes. This time the riser got up to about 200...that still seems a little high to me, what do you guys think about that? There was a little water coming out of the water distribution pump to the engine. I tightened that up as well.
I still need to change the oil on it as well.

 

[intrepidvoyager]

Re: Mercruiser 350 Riser Overheating

Water coming out of the raw water pump means its possible air is getting in on the suction side but first you did not say what the temp of the hoses were going from the engine to the manifold/risers .... if its 110 or there about (normal) that would indicate that the RW pump flow is adequate ....ie , there is enough flow so the bypass water is lowering the engine water temp at 140 to 160 or so down to where it should be before it goes into the manifold/risers.

You did not say if the hoses going to the manifold/risers where hard or can you squeeze them once the engine is warmed up ?????

from your previous flow test it appears that you are getting good flow out of the risers but you still have an issue ...200 is too high for a riser temp.

Anyway check the above and will go from there ...

Have another look at this link ..... hold your hand on means 140 or so .

http://www.acms-usa.com/bulletin_files/hotItem.htm

 

[bruceb58]

fox glastron you should start your own thread with your issue.