Request for help: problems with overheating old Volvo Penta engine

[Kolchac]

From my Yanmar experience:
1. The indirect cooling: fresh water pump is a metal propeller located inside the engine (more effective than yours). The salt water impeller is ~40% bigger, than the salt water impeller for the same engine, just with direct cooling modification.
2. You must be sure there is no air in the fresh water cooling system.
3. You can test the thermostat putting it in boiling water: it might be not open completely. The thermostat is installed only in fresh water system.


Did this indirect cooling system worked before? What cooling liquid do you use?
Why do you think your engine is too hot, - do you see white smoke from the exhaust?

[balticcruiser]

Maybe I'm missing a similar post, but from experience I have seen an electric circulation pump impeller too loose on the shaft. If I remember correctly, on my former MD11 there was a similar pump, and the impeller was just pressed on the shaft without any locking mechanism, just tight. But it had become too loose on my engine, so I had to replace the pump. I think it was replaced with a Mercedes interior heating pump.
So, even though the pump is running, it might not pump effectively, regardless everything else is okay.

[Baba Buoy]

Try flushing coolant passages with HCl dilute acid. It fixed my overheating problem with my old Volvo motor.

[bacchant]

Hi everybody,


Thanks for a very impressive response to my request for help, I am overwhelmed by this forum. I can now report that the problem has been identified and solved!


Since I had covered all parts of the raw water / external cooling system from inlet to exhaust and this worked well as confirmed by the heat exchanger being cold in the areas where salt water circulated, I knew the problem had to be something related to the circulation of the cooling liquid between the heat exchanger and the engine block. Since the mechanical thermostat seemed to work fine, I focused on the electrical pump connected to the heat exchanger.


After input from the forum I tried the following: 1) touch the pump to determine whether I could detect movement (it was hard since the entire engine vibrates quite a lot) 2) use multimeter to test start battery before and after starting engine (alternator charges, but possibly undercharging so I... 3) checked alternator directly (its new and works fine, so I will check the regulator next) 4) finally, I disconnected the pump from the alternator and connected to a separate battery - and that worked! Now I could hear that the pump circulated cooling liquid without turning on the engine. Conclusion: the problem must be related to the electric cables/connection between pump and alternator and/or the engine block (there were some suspicious looking connections - I replaced them with wago connectors). Alternatively, it is the regulator. I will check this too.

Now I have tested the engine for several days using the test setup with separate battery for this particular pump only and the results are quite amazing. I can now push the engine to 1500+ RMP and run at this speed for 5-6 hours (I haven't tried longer because its getting freezing cold..) without problems/insignificant heat (compared to 1-2 minutes before). Before identifying the problem I have been moving forward at "dead slow" speed and 900 RMP for days. Luckily it seems like I haven't caused permanent damage..

Again, thanks to all of you for helping out - I greatly appreciate it! Now my next target destination is within reach again..