new engine overheats

[Pmt133]

Just out of curiosity... is that the thermostat housing from the old engine or is that what came with the new one? Is there a part number anywhere? Does it say alpha on it anywhere? I can't tell from the photos is why I ask. They are different and its simple to rule out.

 

[Scott06]

I can leave my hand on either riser even as the temp gauge reads 200 and the manifolds I can slowly "slap" bare handed without fear of burning myself.. I'm about ready to remove the entire single knob drain system and plumb it old school.

If you cant really leave your hand on them long then they are probably the correct temp. when the thermostat opens (should be if engine is 190-200) it should be feeding water water out of the block to manifolds. If those hoses going from thermo housing to bottom of manifolds are not hot no water is coming out of the block.

before you tear out the single drain system - there is a T feeding the two hoses that go to the elbows. this is where the raw water comes up from the drain 'ball' by balancer. There should be some type of restriction in there - I would look at this and make sure it is not allowing too much water to bypass the block. the T is #20 in this parts diagram- there are a bushing and oring listed below the T as non serviceable parts - Im assuming this comes with the T? Note there are different setups for alpha and bravo

https://www.marineengine.com/parts/mercruiser-sterndrive-parts/350-mag-mpi-alphabravo/0m600000-thru-0w059999/standard-cooling-system-single-and-3-point-drain

you might be able to test this by running it until it gets hotish and clamp off the two hoses feeding the elbows a bit. if this drops engine temp you know where look

 

[svb165]

I can lean on the risers with all my weight and stay there and not get too hot. I was just reading 165-170* + - 4* on both risers even at 195-200 on the temp gauge. they actually get hotter after sitting a while waiting to cool down. the engine read 195*+ so that is getting warmer than the risers.

Just out of curiosity... is that the thermostat housing from the old engine or is that what came with the new one? Is there a part number anywhere? Does it say alpha on it anywhere? I can't tell from the photos is why I ask. They are different and its simple to rule out.

I do believe I used the one off the 5.0 its been too long ,but I thought they were identical, no?

 

[Pmt133]

I can lean on the risers with all my weight and stay there and not get too hot. I was just reading 165-170* + - 4* on both risers even at 195-200 on the temp gauge. they actually get hotter after sitting a while waiting to cool down. the engine read 195*+ so that is getting warmer than the risers.

I do believe I used the one off the 5.0 its been too long ,but I thought they were identical, no?

According to merc they are different part numbers because of the difference in flows... simple enough to check just to rule it out. Now can it cause your issue? Not sure. But if you're bypassing too much water (higher flow bravo housing say) then I could see it.

 

[svb165]

According to merc they are different part numbers because of the difference in flows... simple enough to check just to rule it out. Now can it cause your issue? Not sure. But if you're bypassing too much water (higher flow bravo housing say) then I could see it.

I do feel its bypassing too much since the temps vary so much. I have nothing "bravo" tho. I will check into that right now,, thank you. I thought they were the same part # between the 5.0 and 5.7.

 

[Pmt133]

I do feel its bypassing too much since the temps vary so much. I have nothing "bravo" tho. I will check into that right now,, thank you. I thought they were the same part # between the 5.0 and 5.7.

5.0 and 5.7 are the same. But if the donor engine was configured for a bravo, the housing would look the same but be different internally and have a different PN.... Chances are its correct but still worth investigating. Again. Not sure it'll cause what you're seeing but just worth confirming is correct as well as everything else suggested.

 

[svb165]

5.0 and 5.7 are the same. But if the donor engine was configured for a bravo, the housing would look the same but be different internally and have a different PN.... Chances are its correct but still worth investigating. Again. Not sure it'll cause what you're seeing but just worth confirming is correct as well as everything else suggested.

thanks yes I'm looking at everything at this point. it is the same housing listed for both 5.0 and 5.7 with the single point drain system. same stat too. 160*

 

[Scott06]

According to merc they are different part numbers because of the difference in flows... simple enough to check just to rule it out. Now can it cause your issue? Not sure. But if you're bypassing too much water (higher flow bravo housing say) then I could see it.

Doubt the flow rate between bravo and alpha housings is different as it’s the same engine . Most likely related to hose locations and water flow given bravo is engine driven raw water pump and alpha is in the drive so flow path from transom housing is different

 

[Pmt133]

Doubt the flow rate between bravo and alpha housings is different as it’s the same engine . Most likely related to hose locations and water flow given bravo is engine driven raw water pump and alpha is in the drive so flow path from transom housing is different

I think externally they are identical. But yes. I don't think its the issue... just worth checking.