Rust in thermostat

[scoflaw]

Raw water cooled 502 that keeps getting rust stuck in t-stat preventing it to come up to temp.

​Has happened a couple of times. Looking for a quick fix to get the engine temp up enough to flush the rust out.

​Pain in the butt to pull t-stat and clear it..

​Suggestions welcomed. Thanks

 

[alldodge]

Have you ran it without a TS with an attempt to flush?

 

[Scott Danforth]

let me guess, you boat in salt water

sell boat, buy one with fresh water cooling.

the rust is coming from inside your engine block. and no, you cant add fresh water cooling at this point.

 

[Lou C]

Ahh well we have all dealt with this, the longest I have been able to use a thermostat has been about 4 seasons. One thing I've done (sounds crazy but it worked) was this:
When you get the cold running at 100*-120* at idle; I've run it on plane long enough to get it up to 160*. Then let it drop off plane and bring it back to idle. before it cools off, Take a small hammer and tap all around the thermo housing and on the intake below the Thermo housing. This may jar the rust flakes loose and the t stat will close enough to get the temp up to normal.

The other thing you could try is to pick up some extra front circ pump gaskets. Drain the block. Remove the front circ pump. Then rig up a way to feed low pressure water into one of the water pump homes on the block. That way you can get more of the rust flakes out. About all u can do. I carry spare t stats, gaskets and gasket sealer.

 

[scoflaw]

So this motor runs fine all summer, now I have had this issue twice in the last 5 outings. Easy enough to clear if I pull the stat out, but looking for a way to clear it without pulling it

​It's not stuck open much, maybe an 1/8". And it doesn't have to open much further to clear itself. Beating the boat on plane doesn't do it. Was thinking of a way to block off some water flow to get it to heat up without burning up my shutters. It's a trailer boat, so also thinking about running it in a tub of hot water.

​Any ideas ?

 

[Lou C]

If you're saying that running the boat on plane does not get the temp up to normal, then the stat itself is probably sticking, normally the water flow at those rpms flushes the rust flakes out all by itself. I'd say you need to change the stat.
Its a pain, yes. My next engine will be new and will be closed cooled for sure.

 

[scoflaw]

The stat is new. The ocean is getting cold, and this seems to be a very cool running engine. Like I said, the stat is only open about an 1/8", so I must have a ton of flow. Going to try clamping the circulating pump hose shut, see if that opens it up. Stat performs nicely in a pot of water, that's how I cleared it the last time.

 

[Scott Danforth]

the issue is you have raw water cooling and you boat in salt water..... rust is flaking off the inside of your water jacket. any bit of crud holding your thermostat open will prevent the thermostat from getting warm enough to open all the way to allow the stuff to come free. the only solution you have at that point is to periodically pull the t-stat and clean.

you can flush your block and heads with a mixture of oxalic acid which will help remove some of the rust. requires making a service loop of coolant with a tub and an electric pump

out of curiosity, when was the last time you replaced your manifolds and elbows? you may want to inspect them.