Overheating, can't find the culprit

[Scotty Mac]

I need some help. Last year my '93 SNOB was running great. I replaced the thermostat as a maintenance item (it was over 10 year old). Since then I've had 5 thermostats, all new hoses, replace the water pump, replaced the impeller pump and impeller and also replace the flush valve. I got the boat out this weekend to get it ready and the temp went up to 180 sitting in the driveway. With the thermostat removed, the engine temp is cold. Put the thermostat back it and I up to 170-180. This boat ran for 20 years at 150 degrees (has a 143 degree tstat) and now it runs over 160-180 on the water. Any suggestions!

[eyekode]

Overheating, can't find the culprit

Are you sure it is actually overheating? It could be your gauge or your sender.

Also does your boat have a transmission cooler? On some this can restrict the flow of water if crap is in it.
Good luck!
Salem

[Zach@n3]

Scotty, are you sure you didn't get ahold of an EFI thermostat instead of a carbureted thermostat? Your temp sounds very normal for a 160 degree T stat instead of a 143 degree.

[bhectus]

If it is running a consistent 180, i wouldn't worry too much about it. If it is fluctuating, then you may have an air leak somewhere, or a blockage. Trans cooler as eyekode suggested could have debris in it. Or if you have shredded an impeller in the past it could have pieces clogged in the exhaust risers. I found quite a few in mine after my last impeller gave way.

[Scotty Mac]

All very good suggestions. I'm looking into the sender and gauge. I'm just not sure what the range should be for the old sender, so probably just buy a new one and move on. The Tstat is a 143 degree I'm told, that's why I've been through five. PCM sent me several to try and told me they had a bad "batch." I put them all in hot water and there was one that started to open at 150 degrees, so that's the one that's in the boat. bhectus, I've just rebuilt my exhaust towers and they were good, flushed them anyway and got some rust out, but never had an impeller shred. Eyekode, the transmission cooler is clear as well, can see right through all the holes. I'm just at a loss, I've never had something like this happen. When I changed the 1st Tstat out last year, the Temp did hit 200+ before I could get back to the dock, so I'm still wondering what I may have done to a 20 year old engine that has effected the cooling system. Maybe I should have started with the gauge and sender. Obviously resistance is working and the gauge is indicating, but I don't know what my resistance reading should be for the sender I have. Thanks for your reply's guys, any other suggestions are greatly appreciated.

[Zach@n3]

200 won't hurt anything. That engine in a truck towards the end of its life probably ran a 210 degree thermostat. I would ohm out the sensor while it is running.

[lucky7t]

A good test would be to buy or borrow a temp gun. It shoots a lazer at the part and tells you the temp. This might help you test the gauge.

[DanielC]

I would suspect an air leak, in the suction side of the cooling system before thw raw water pump.
see this thread about a flushing adapter I made.
http://www.planetnautique.com/vb3/sh...ushing+adapter

you can use this adapter to pressureize the cooling system, before the raw water pump. Usually that makes any air leaks apparent.

[TRBenj]

200 won't hurt anything. That engine in a truck towards the end of its life probably ran a 210 degree thermostat. I would ohm out the sensor while it is running.

Its not the 200 degree water that will do the damage... its allowing the engine to get that hot and then shock it with (relatively) cold lake water that will! 200 is about the limit that I feel safe pushing it during an overheat... any hotter, shut it down.

I agree that if youre running a consistent 180, I'd be suspicious of the thermostat. Sounds like a 160 'stat.

If youre seeing 20+ degree swings in temperature, especially when idling for extended periods of time or after a hard run and returning to idle, I'd suspect an air leak. Inspect all hoses, tighten all clamps. Strainer bowl needs to have a good gasket and be installed TIGHT. Make sure your hoses arent overtightened on the tranny cooler- that is soft copper and can deform, allowing air to leak past.

[Scotty Mac]

Guys, sorry for not getting back sooner to wrap up, been on the lake. Don't know which did the real trick, but I put the new sender in and at the same time pulled the Perko Flush Pro OFF and guess what? I'm constant at 155 almost all the time. Perfect Water temp. Thanks for your help and suggestions.