440 overheating

[Targojoe]

Hi all...I've tried everything!! my starboard motor is overheating...i can idle all day long...once i bring her up to 3k rpm antifreeze blows out the overflow...here's a list of what I've done:
1-pulled her out of the water and cleaned the screens and through hulls...both through hulls were 60 - 65% clogged...i though this was it I was so happy...
2-I've replaced the thermostat
3-i've reverse flushed the transmission and oil coolers with a hose and a shop vac
4-I pulled the elbows and risers...cleaned those (they were only a couple years old) while those were off I cleaned the exhaust manifolds...

when running the risers are cool...the bottom of the manifolds are hot but the tops are cool...

I have great water flow...what am I missing???

[prowlersfish]

Have you cleaned the heat exchanger ? Cleaning the raw water side you may need to use something like rydlyme . Flushing with a hose won't remove build up . Raw water impeller and pump cam should be checked .

[WayWeGo]

Not sure how your fresh water cooling is plumbed, but on our boat, the manifolds are fresh water cooled and the exhaust cooled by raw water. If your risers are cool but the manifolds are hot, you should be looking for a problem on the freshwater cooling side of things.

If you have an infrared thermometer, look at the temperatures around the heat exchanger. The raw water should be cool coming into the exchanger and leave the exchanger 5-10 degrees warmer. The coolant should leave the exchanger significantly cooler than your thermostat setting.

If your coolant is coming out cool and the raw water is not getting a significant rise, then you should be looking for a circulation problem in the antifreeze side of the system. If your coolant is coming out hot and the raw water has a significant rise, then the raw water flow through your heat exchanger is being impeded and it needs to be cleaned.

Since your port engine is not overheating, you can compare temps between the same points on each engine and that should also help point you in the right direction. You can pick up an infrared thermometer cheaply at Harbor Freight, or if you want a nicer one, I have and like a Fluke 62 MAX Plus IR Thermometer which will run you about $125.

[Big D]

I agree with the above. If your intakes were that clogged, chances are so is your heat exchanger though your oil coolers are typically first in the circuit.

Flow and volume can be deceiving. What may seem normal is often not enough to do it's job. The impeller may be suspect here as well.

I'm not assuming anything so I'll ask; what does your temp gauge say, and have you confirmed that temperature at the block? Too much coolant in the heat exchanger to begin with will overflow once it reaches a certain temperature.

[Targojoe]

I forgot to mention that I did remove the heat exchanger to have it cleaned an tested...all clear!

The exhaust manifolds are definitely raw water cooled...

The only thing that has antifreeze is the block...

[larryeddington]

Years ago I had a car that overheated anything off idle. It turned out to be the advance mechanism. The was a long time ago but symptoms were like yours. On that on had a mechanical and vacuum advance which I doubt you have the vacuum. But the mechanism could be stuck, rusted etc. I would check that for sure. It is worth checking anyway.

[WayWeGo]

Lots of good advice here. It sounds like you have checked most of the raw water side of things, and the cool risers tend to indicate that you have cool water flowing through the whole system, exiting through the exhaust. Not that you definitely are problem free on this side, but it seems less likely your problem is on the raw water side.

I still think you should look at the temps at the heat exchanger, on the input and output sides of both raw water and antifreeze circuits. That will help you isolate where the problem is so you can use a top-down logical approach to finding the area where you have a problem. Otherwise, you can end up spending more time and money on a shotgun approach.

If you don't have an infrared thermometer, they are quite valuable on a boat. Not only can you check the cooling system, but also your stuffing boxes, batteries, oil temps (at the filter or pan), transmission temps, etc. Probably one of the most used tools on our boat.

I saw one on Amazon for $14 shipped, and Harbor Freight sells them for $30. The HF model seems to be quite popular with boaters. You get what you pay for, with the more expensive ones being a bit more accurate and typically having a more narrow beam so they can be used from longer distances and still look at a small area.

[P-Dogg]

Let's not forget to mention that an IR thermometer is great for checking to see how cold the beer is......

[WayWeGo]

I have heard that a few boaters on another forum have checked their wives foreheads to see if they were having a hot flash. Unfortunately, that resulted in broken infrared thermometers and having to explain the black eye at work on Monday...

[Barrie]

Let's not forget to mention that an IR thermometer is great for checking to see how cold the beer is......

Sorry I can't add anything useful to this thread, but this made me laugh more than maybe it should have.
I bought an IR thermometer about 6 months and haven't pointed it at anything that the inventors likely considered someone taking a temperature of.... my dogs, the street lights across the street, moonshine leaving my still, the difference between tile floor and hard wood and the temp of my whisky with and without ice

Sorry I'm done now