Author Topic: THERMOSTAT BLEED HOLE SIZE ? (Read 18657 times)

xyzer · « **on:** March 20, 2009, 07:08:36 PM »

I was thinking(

) the other day while my oid was warming up what if we used a larger air bleed hole in the thermostat. I watched as the temp gauge it climbs up to 190 or so then it opens and gets a shot of cold water and drops back down to 100 or less. This cycle repeats over and over until the cooling system gets warm then it will stay at 200 or so. If we used a larger hole in the thermostat it would allow more flow and it would eliminate some of the cold shock. Do I make any sense?
Dave

compig · « **Reply #1 on:** March 20, 2009, 07:17:25 PM »

Can see where your coming from , try it and see. Worst case is a new stat if it doesn't work.

Tom · « **Reply #2 on:** March 20, 2009, 07:32:39 PM »

That would also slow down the warm-up. Perhaps it would be best to place a gate valve on the outlet and adjust it so the the engine has just enough flow to cool under full load. Then when the thermostat opens there might not be as big a gulp of cold water.

Best would be a housing that bolts to the outlet with recalculation to inlet. Could be a new product???

I felt the temp changes you describe on mine too. I have an 1/8" hole in my thermostat. I wonder if there are any slower reacting thermostats out there?

xyzer · « **Reply #3 on:** March 20, 2009, 08:21:40 PM »

compig,
I agree no big deal! I'm going to try it and see what happens. I have data on the time it takes to get to full operating temp so I can compare.

Tom,
My thinking is it will take about the about the same time to reach full operating tempeture without the hot cold cycles. A more constant rise instead of 200 open 40 in (on a cold day) close heat er up again. Basicly the hole is the gate valve and if it is a bit to much of a restriction the stat will open to allow more circulation.

Stan · « **Reply #4 on:** March 20, 2009, 10:03:00 PM »

The only reason to have a hole in the thermostat valve, NOT the outer flat plate, is to release the air in the system while filling it up for the first time. In theory, once you have run it the first time, there should be no air in the system anymore. (unless you have it bolted to Vancouver Island

Stan

ronmar · « **Reply #5 on:** March 20, 2009, 11:57:41 PM »

Quote from: xyzer on March 20, 2009, 07:08:36 PM

I was thinking() the other day while my oid was warming up what if we used a larger air bleed hole in the thermostat. I watched as the temp gauge it climbs up to 190 or so then it opens and gets a shot of cold water and drops back down to 100 or less. This cycle repeats over and over until the cooling system gets warm then it will stay at 200 or so. If we used a larger hole in the thermostat it would allow more flow and it would eliminate some of the cold shock. Do I make any sense?
Dave

Dave
I don't recall what you are using for a cooling system? A larger thermostat hole should ease the severity of the temperature swings by allowing a steady flow of cool water to enter the engine. It may actually shorten warmup time. Warmup time is a factor of BTU generated, coolant mass, BTU dissipated and temp difference. By allowing a steady flow of cooler water into the cylinders, you maintain a greater temp difference between cylinder wall and coolant, and have a higher heat transfer rate.

The flow will be dependent on how much heat you are putting into the fluid, and how big the hole is. I agree that if it is too small, the temp will rise, and the thermostat will open and cycle to take up the slack. The area of the hole could be as large as the thermostat opening at normal operating temp and a very light/no load. The thermostat would open and regulate the temperature at any greater heat input.

Stan · « **Reply #6 on:** March 21, 2009, 01:18:27 AM »

I was just teasing you Jens...good to know you're still paying attention

Actually, if the thermostat is installed the correct way, that is with the bimetal spring on the hot side, as the water cools just below the temperature of the bimetal spring activation, it will start to close very slowly, thereby throttling back on the flow but never quite stopping it. I would advise xyzer to take his thermostat out and put it in a pot of water on the stove and watch it while it boils. (yes, a watched pot will still boil!). You will then see the action that it uses. These things don't "snap" shut, they move at the pace of a Galapagos tortoise! There's no way it should act as described if it's functioning normally.
Stan

xyzer · « **Reply #7 on:** March 21, 2009, 02:42:31 AM »

ronmar,
I thermo siphon with a metro radiator on one oid, and a Saturn on the other. They both exhibit this trait. My thoughts were as you explained but you did a better job!

Stan,
Yes I could have a defective stat......But I see this behavior on both of my oids....also I have heard of others observing this behavior. If I put the stat in a pan and wait for it to open then throw in a cold pan I bet it shuts. Wait for that pan to hit 190 it opens then throw it in another cold pan it will shut until I run out of cold water. Now if it had a pump and a bypass we would have another story. Like I said I was just thinking
Dave

MacGyver · « **Reply #8 on:** March 21, 2009, 02:59:56 AM »

Thermostat "gulping" s a common occurrence in lots of automotive systems.
FWIW, lots of Subaru cooling systems (and maybe other manufacturers) have the thermostat on the *inlet* side of the engine instead of on the outlet...

NoSpark · « **Reply #9 on:** March 21, 2009, 04:54:45 AM »

I took out the 195° thermostat and put in a 180° with a 3/16 bleed hole. If it wasn't such a pain to drain and refill I would take it back out and make the bleed hole even bigger but it does work much better. I'm tempted to take the thermostat out all together and regulate with the fan and temp switch, it may take more time to warm up but it would be a more even heat up.

Speaking of inlet thermostats. Another form of cooling is reverse flow cooling, where coolant flows through the head first and down through the block. For gas engines this means cooler heads so higher compression ratios and more spark advance can be used and the cylinder to head temps are more even. Maybe this would be an advantage for diesel also. Of course you couldn't do this with thermosiphon.

xyzer · « **Reply #10 on:** March 21, 2009, 05:11:33 AM »

NoSpark,
When I have it apart I'll try a .225 and see how it does!
Dave

ronmar · « **Reply #11 on:** March 21, 2009, 05:12:23 AM »

Nospark, Why did you opt for the lower temp thermostat?

NoSpark · « **Reply #12 on:** March 21, 2009, 06:32:10 AM »

I put in the lower temp thermostat with a bigger bleed hole to get the whole system up to temperature faster. With 20F ambient temps the engine temp swings were huge until it ran for a long time, even with a 3000+ watt load. At the same time I installed a much smaller radiator and 50/50 antifreeze. It still takes a while to heat up but warmer weather will be here soon I hope. I have a 120v fan mounted behind the radiator, I just need to find a safe place for the 120f snap switch to keep the fan off until the engine gets up to temp. I found out that a plastic radiator tank does not transfer heat to a snap switch very well, even with thermal grease.

oliver90owner · « **Reply #13 on:** March 21, 2009, 08:39:23 AM »

Not sure wher Stan gets his 'bimetal sping thermostats' from - mine have been wax operated for as long as I remember, and I am old.

Not one has adressed/mentioned the other possible problem of a faster warm up. Reduce the water volume to the minimum required and the heat required will be at the minimum. If yours is way oversized with metres of extra tubing that might be a much better place to start.

Jens point about the 'stat not getting hot was just a little off beam - who else would put a stat at a lower level than the engine outlet and expect it to work properly? If it is elevated, the hot water will rise and operate it correctly.

If you have a pump and a 'stat there should be a bypass, or the pump will be pumping into a closed head which is not so good for it - even an impellor pump.

Maybe a smaller 'stat might be beneficial, instead of one designed for a 60HP engine. Big pipes were OK for thermosyphon in 1920s with sediment, no antifreeze/corrosion additives etc. Designs have moved on a pace since then. Apply a little mathematics to the well documented design requirements for the cooling system and come up with the minimum flow needed for the worst case scenario and I would think the flow rate can be reduced by quite a percentage of what you are experiencing now. Think hottest day, highest load - thermostat should remain open and temperature might rise a few degrees above that opening temperature, but engine should not overheat - and you will close to the optimum for the design parts you cannot change.

Me? Let it thermosyphon. I don't run mine long/often enough to worry about it. KISS.

Regards, RAB

compig · « **Reply #14 on:** March 21, 2009, 09:43:50 AM »

Quote from: NoSpark on March 21, 2009, 04:54:45 AM

Speaking of inlet thermostats. Another form of cooling is reverse flow cooling, where coolant flows through the head first and down through the block. For gas engines this means cooler heads so higher compression ratios and more spark advance can be used and the cylinder to head temps are more even. Maybe this would be an advantage for diesel also. Of course you couldn't do this with thermosiphon.

Mitsubishi used this method on their Evo from version 6 onwards. Quite a critical application though with almost 300 BHP from a 2 Ltr 4 cylinder , and this is before people like me start fiddling with them to obtain obscene amounts of power , currently 450'ish on mine !! The engines still bullet proof though ,even at this power and much higher !!

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