Will running cold cause engine damage?

[nightowle]

Without getting into a long story, my A4 is running without a thermostat (the PO took it out and the intake from the water pump to the thermostat housing is blocked). The engine used to run hot, but after a flush it has run progressively cooler from about 140 down to around 100 now. I have replaced both the sending unit and the temp gauge, both of which are operating correctly. the water here in Puget Sound is still cold these days, but the engine stays at 100 or 110 degrees. My question: other than fouling the plugs more quickly and getting less than optimum fuel mileage, will low operating temps hurt the engine long term?

[sailingdog]

It will use a lot more fuel too... and it won't be able to burn off the carbon deposits or moisture—which will cause serious maintenance problems in the long term. You're better off restoring the thermostat and fixing the problems than using it with the systems mickey-moused...

[nightowle]

I'm just concerned that I'll mess with the system and it will start running hot again!

[jaschrumpf]

It's an awfully simple cooling system, so I wouldn't worry too much about that. If it ever runs hot again you can install the manual thermostat bypass valve that Universal actually recommended for these engines. You can get a look at one here at the Moyer Marine Atomic 4 site. You can get all the parts at your local hardware store, but this gives a good picture of what it looks like installed.

I put one on my boat because I have the opposite problem and run a bit hot. I have yet to flush the cooling system, but it's on my list of things to do for this spring.

Good luck!

[Piratesoul]

I have the same issue as nightowle and I have the the manual bypass valve installed. The PO removed the thermostat. I once opened the bypass valve and forgot to close it. On my next sail the engine shot up to 200F. I wonder if I should just use that valve occasionally to run the engine hotter to get rid of deposits and moisture? What do you guys think?

[JimsCAL]

The proper temp is 135-150F. Hotter than that and you will get scaling in the engine passages. Lower and you get engine deposits and other problems. If necessary, adjust the manual bypass valve to get the watre temp within that range. The Universal 140F thermostat seems to have problems working effectively without a little resistance in the recirculation line.

[Piratesoul]

Thanks JimsCal, great idea!