350 mag mpi overheats only at idle

[silver_power]

Hello, my 2009 350 mag mpi (1A348183) alpha one genii drive, running hot when it is on idle. To be more specific: when running cruise and wot the temp is steady 71-73 degrees C (160-165F) but when returning at the dock and idles the temp raises till 85-88C (185-190F) not more. If I push the throttle to 1000rpm, the temp drops. Manifolds-raisers - impeller new. The thermostat was changed 1 year before as then was the first time the engine overheated but the reason wa's the blocked manifolds. The mechanic then gave me a 75c tstat instead of 71c which is the standard rating for my engine. So now I have 75c tstat. Is it possible that this is my problem?....meaning that the engine runs hotter and when it dles, the low water supply of the alpha drive at idle can not cool down the engine fast?

 

[silver_power]

I must mention that it is open cooling , running seawater and already back flushed. ......

 

[Bt Doctur]

Your not moving enough water at idle, that is usually a weak/worn impeller.

 

[alldodge]

+1 agree, not enough water

I don't see increasing the thermostat temp as the issue, and this can make things worst in open cooled salt water environment. The higher temps can cause the salt to erode the cast iron faster

When was the impeller last changed and the pump housing inspected/changed?

Do you have the 3 or 7 point drin system?

If you have the 3 point drain this can also cause some issues as there are other items which can restrict water flow in one area or another

 

[silver_power]

I just changed the impeller and it has the 3 point drain system. I am also aware about the salt deposits to the cast iron and that is why I am thinking of changing the tstat to 71c degrees. ...this issue occurred right after tsat change.....

 

[alldodge]

Assuming your pump housing was in good shape, I would look at item 2 the check valve, distribution drain housing, item 20 the Tee and item 9 the manifold. Something has increased a restriction in the main feeds so water is going in other directions and not so much in the main feed lines

 

[thumpar]

Going to a lower thermostat will help prevent salt issues but I know an MPI likes warmer temps so it is tough with a raw cooled MPI in salt. I would probably go with the lower temp just to keep the salt problems at a minimum.

 

[silver_power]

I put out my thermostat and the serial is 8M6002715 . My engine normally has the 8M019441 tstat....I ordered the correct today and I will check it. I made a mistake, my engine is a single point drain system. What else can I check? New manifolds and raisers, backflushed the system, new impeller , new gaskets and checking-brushed the housing (it was very clean and in good condition). What else can I check?? I want to find the problem before I put the bist into the sea.....

 

[alldodge]

Is this a new to you boat, or have you had it a while and it just started this?

 

[silver_power]

Last year I had overheating problem for first time, and I bought a tstat from my mechanic. I Change it but the overheating was still exist just because the problem was that I had rusty manIfolds. But then the problem was that the temp was high while cruising and not at idle. Now with the new exhausts and the tstat I had changed last year, the temp while cruise and wot is normal and when I slow down@idle the temp raises. Now I have the boat out if the water and try to find the problem while it is with muffs, the temp raises at idle and if I accelerate to 1000rpm, the temp drops......I can not understand what is the problem since I thought that my problem would be solved with the impeller change.

 

[alldodge]

Pull the large hose off the circulating pump and look up inside at the vanes. Rotate slowly to look at all vane, then use a screw drive or other to try to keep vanes from moving while you turn the pulley by hand

I that's good then its either the pump housing, impeller is wrong size or type, or the hoses and parts on the single point drain has an issue. Something is keeping most the volume of water coming out from the drive to go to other places

 

[silver_power]

I will check the circulating pump with the way you are telling me. I hope there to be the problem.
I will post after the check. Thank you very much

 

[silver_power]

I am thinking......has ever happened the circulating pump to fail to a 450hr engine?? I think is little early....I hope this will be the problem.

 

[alldodge]

Normally no, but could be from a factory defect. Might not be it, but just searching possibilities

 

[thumpar]

Circ pumps usually fail because the seals go and take the bearings out. I would say that is not the likely problem but always a chance. Before I did the pump I would rule out the other possibilities.

 

[silver_power]

In any case I will pull it of for inspection and for that I already ordered the two gaskets needed. Just a thought....as now I pull off the tstat housing is there a problem to throw inside the engine water with the hose? Can I do the same inside the two holes I will see as soon as I pull off the circulator pump?

 

[QBhoy]

I’d be back at the impeller and it’s assembly. Defo not pumping enough water at idle.
Have you started it out the water at any point since changing it last ?
I have a similar engine and it runs right on about 152 at idle and anything up to about 3500 rpm. Only time it will go above is by giving the boat silly trim and wot, but never goes aboive about 170, even then. .

 

[silver_power]

The impeller is totally new, and gaskets as well. Zero hours,only test on muffs. The housing perfect as well inspected. The only staff I did not change was the orings inside the water hose outgoing the impeller housing, but the old seems good. I will back flush again the block and check the hoses. And also check the circulation pump.

 

[thumpar]

Test it in water.

 

[FreeBeeTony]

Maybe your hose isn't supplying enough water?