Overcooling - what are the effects on the engine

[Razorfish]

Morning all,

just pulled the thermostat out of my YSM12 and it is stuck wide open. What are the effects on the engine of a over cooling?

I was wondering as I noticed that there was a lot of soot in the exhaust water the other day but put it down to the engine being under a bit of load against tide/very fouled bottom.

Cheers

 

[Lon nan Gruagach]

Think of the difference between permanently open thermostat and properly working 90^c. For permanently open the water will sill et hot, just not as fast or to the full temperature, maybe 50^c to 70^c. Compare this to the heat source (inside the cylinders of maybe 700^c* and the relative difference is tiny. (700-50 vs 700-90 or about 6%)

*Wild guess taken from exhaust gas temps.

 

[Razorfish]

Hmm, I hadn't thought of it like that. I assumed that the amount of water flowing through the water jacket around the cylinder would be sufficient to cool it quite considerably. But hey, I'm no engineer hence my question.

 

[VicS]

Morning all,

just pulled the thermostat out of my YSM12 and it is stuck wide open. What are the effects on the engine of a over cooling?

I was wondering as I noticed that there was a lot of soot in the exhaust water the other day but put it down to the engine being under a bit of load against tide/very fouled bottom.

Cheers

Probably excessive condensation of water in the oil and in the cooler parts of the engine, eg in the rocker chamber and the crankcase breather (???) leading to build up of an oily emulsified sludge, although the YSM12 does not normally run at a very high temperature. The thermostat begins to open at 42C and is fully open at 52C.

( not sure where Dougal Tolan is getting his temperature figures from)

If the thermostat is difficult to get or stupidly expensive it may be possible with a bit of descaling, thermal cycling and gentle persuasion to get the old one operating again .......... I freed up my outboard engine thermostat in this way when I unexpectedly found it stuck fully open

 

[Razorfish]

Thanks Vic.

I'll have a look for what you describe - reminds me of my old Morris Marina (it was free) when the head gasket went, yuk.

I found one for £25 but was going to see if I could free up this one as I like a challenge. It keeps me out of the pub.

 

[neil_s]

Another successful thermostat rejuvenator, here! I favour Fernox DS3 for descaling.

Scale build up is a problem for raw water cooled engines, so they don't normally work at over 60 deg C to keep it under control. My Bukh DV20 needs a clean out every five or so years, even so!

 

[Razorfish]

Even though I've ordered a new thermostat I soaked the duff one in vinegar for an hour and gave it some heat. It is now not duff at all so have kept it for a spare.

Hopefully there hasn't been an ill effects on the engine.

 

[reeac]

My old MGA has a very good ether-based temperature gauge and I can see from it that when the engine is up to temperature the thermostat opens and closes perhaps 5 or 10 times a minute, thus determining the engine running temperature. It follows from that that a thermostat that is stuck open will result in the engine always running too cold. It's not just a matter it warming up too slowly. There's a tuning mod. for MGs that run too hot when used in competition .... replace the thermostat with a baffle plate which has a judiciously sized hole which is alleged to permit the correct flow of coolant to keep the engine at the correct temperature.