OK kids, I have a small problem with a Volvo Penta 5.0 engine in my boat.
Last week it overheated,(+210 degrees F) this due to a bad impeller on the raw water pump.
This has now been replaced, but the engine still overheated after the replacement impeller was installed.
So out of the water it came, after looking at the thermostat I found small bits of the old impeller inside the housing, so I cleaned out the housing, and back in the water it went, it still over heated, though not as bad,(under +200 F) out it came again, this time I looked at the main circulating water pump, found nothing, and tested it, it worked fine.
So, I pulled all hoses and did a thorough cleaning, then a complete back flush of the engine block with the water pumps, and thermostat housing off the block, I made adapters to block off the one side of the water pump and one to push water through the thermostat entrance, this was a backwards flow, ran the water at street pressure for 10 min, I didn't see anything come out the discharge tube into the 5 gallon bucket I used to catch anything if there was anything blocking the water passages.
I tested the thermostat by boiling it in a pot of water, it opened right at 167 degrees F, and was fully open at 174 degrees F, so it's not the problem.
I tested the thermostat water sensor buy using an ohm meter and a pot of water on the stove, this along with a calibrated digital thermometer gave my the resistance readings for a wide range of water temp's, I know now that at 210 degrees I will have 64 ohms at the sender, and around 760 ohms at 70 degrees.
This way I can tell directly at the engine if the water temp gauge is right or not.
Now......Is there a filter somewhere that I am not seeing???? And if it still overheats after all this do I need to pull the heads to look for blockage?? (Not a job I'm looking forward too)
This is looking to be a big project, I don't want to take it in to the service center as that is a bit above my budget right now, any advice from you boat guys will help.