persistant overheating issue.

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woodguy81

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I have a 2004 mercruiser 6.2 mpi. serial number is gone. cooling system is closed cooling with the coolant that flows through the manifolds as well as the block. This engine has been overheating since i put it together last year. This was a new long block. Here is what ive done and where im at.
1. new water pump and impeller. Tried this a few times.
2. replaced the through hull line (bravoitis was setting in)
3. Checked every line for blockages as well as the heat exchanger
4. engine circulation pump appears good and solid with no noise or play in the shaft. It has the bronze bidirectional impeller installed.
5. thermostat starts to open in a pan of water at about 170


The engine runs at least 20 degrees hotter than my other similar one. Same engine slightly different closed cooling system. One has the dry joint exhaust and the other has the wet joint. The alarm goes off after a short time that its overheating. can get it to come down just enough to clear the alarm by running at least 2500-3000 rpm. I currently have the entire system tore apart. Only noteworthy thing is the when flushing the coolant side of the heat exchanger it came out brown and dirty. the side of the thermostat facing the exchanger is also dirty. coolant flushed from the block and manifolds is greener and cleaner.
 
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tpenfield

tpenfield

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Have you taken the end caps off the heat exchanger to check for calcium build-up blocking some of the tubes? BTDT. :oops:
 
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woodguy81

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havent tried on the hose. It overheated after a short run at 3000 rpm then coming back down to idle it started with the alarm. The temp according to the Diacom computer reading in the spring was around 188 while running at 3000 rpm. that was with 55-60 degree water coming in from the lake. it is now over 80 degrees in the lake so im guessing the problem was there before but the cooling water was a lot colder before. Ill try the thermostat. I never changed it. It starts to open at 170. fully open by 185. just checked it again.
 
Fun Times

Fun Times

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Yes. buy a new thermostat then check it the same way you do before you install it as it may help give some indication…. 188 is to warm.
 
tpenfield

tpenfield

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I would get an IR thermometer and get temperature readings all throughout the cooling system, particularly when it is running hot.
 
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woodguy81

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Bondo said:
Ayuh,..... Which one are we talking about,..??
Click to expand...
the problem engine is the dry joint one with the coolant that runs through the manifold as well. guess it is called a full system vs the half system that is on the other engine.
 
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woodguy81

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Fun Times said:
Yes. buy a new thermostat then check it the same way you do before you install it as it may help give some indication…. 188 is to warm.
Click to expand...
Bought a second 160 degree thermostat. different brand. they both start to open at 170 in a pan of water at identical rates.
 
Lou C

Lou C

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Does using the outdrive water pickup provide enough volume of water flow for full closed cooling? I’d think that it should if Merc sold it this way OEM.
You’re having an overheating problem on the engine that had full closed cooling but not on the one that doesn’t, correct? I’m wondering if you’d be better off with the thru the hull water pickup. Is the heat exchanger on the problem engine an OEM or after market unit? Is it sized big enough for the extra heat load of the exhaust manifolds?
 
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