Bukh dv20 thermostat

[afterpegassus]

The engine temp alarm went off today. Impeller ok and plenty water at the exhaust. Because the block felt hot I suspected a stuck stat. On removal and placed in hot water it opened fine, but when reassembled and run the alarm went off again. Perplexed, I removed it again and reassembled without the stat. When run, no alarm and cooler block.
Is the stat goosed?

 

[Poignard]

Just a thought. The block housing the thermostat is cast iron and becomes corroded and scaled. Is some of this build up of material preventing the thermostat opening?

 

[Seanick]

Is the small 'dribble' hole in the stat clear? If there is not one a 3 or 4mm hole drilled to allow some water into the head to activate the stat and prevent air locks. Very slightly slower warm up but can can cure a lot of probs.

 

[christo2024]

I think twisterowner is right. I had overheating problems on mine and Bukh advised me to take the exhaust manifold off (easy job)and clean it. They were right. It was very badly scaled and the cooling water holes were almost closed with corrosion.

Its very likely that corrosion and rust could prevent the stat opening

 

[afterpegassus]

The cleaning out the crud suggestions seem reasonable and I'll get to grips with that today. At £67 a time I'm reluctant to replace the stat when it appears functional.
Thanks for the suggestions.

 

[afterpegassus]

for the interest of those who posted, after cleaning, all appears well.