Drilling the thermostat??

[undy]

Rick,

I'm seeing pegged-out 250 deg spikes! The needle swings to the 250deg mark and then right away starts to drop, only on the first warm-up.. The only thing I can imagine is that there's a recurring pocket of steam that travels past my temp sending unit shortly after start-up. I can actually jump out and feel the coolant part of the intake near the sending unit when it shows 250 deg and it feels fine (no where near what 250 deg should feel like). It's still doing it with 2ea 3/16" holes in my t-sat. I'm going to replace the thermostat (again) and drill the new one with 4ea 1/4" holes this time. I also, as I did before, test it in a pan-o-water on the range w/a thermometer in it. I had the March pullies, actually still have the water pump pulley. I changed the crankshaft March pulley to an OEM larger diameter crank pulley, giving me an overdriven waterpump (overdriven by +0.05%). As I said my cooling capabilities are fine, just that darn temp spike that's driving me nutz!

[Tom Kirkham]

The bypass is to keep the coolant circulating to prevent steam pockets from forming in the heads while the thermostat is closed. If the water flow is stopped (no bypass hose, and a thermostat with out holes drilled in it) then you have a formula for getting localized steam pockets in the head. The problem with holes in the thermostat is the delay in the engine warming up. Another help in preventing steam pockets is running higher pressure radiator caps. On our billet surge tanks we are running 20 PSI caps. F1 cars for a while (until it was banned) were running closed systems... On stock surge tanks you can only run about 13 PSI with out the tank ballooning. Another issue with steam pockets is that because steam dos not carry away the heat, as well as water, you also get hot spots in the combustion chamber... This can also lead to detonation...

[Tom Kirkham]

The bottom line is you need to keep the coolant moving. You should run either a restrictor, holes in the thermostat, or a coolant bypass.

[Tom Kirkham]

An interesting article:
Evans Cooling Systems, Inc. High Performance Engine Cooling and Power Production.

Note: I am not advocating their coolant. Just giving the reader food for thought.

[undy]

Originally Posted by Tom Kirkham

An interesting article:
Evans Cooling Systems, Inc. High Performance Engine Cooling and Power Production.

Note: I am not advocating their coolant. Just giving the reader food for thought.

I looked at that Tom.. but .. The heat rejection factor of the Evan's coolant is well below water and a water/glycol 50/50 mix, 75-80% compared to water (100%) if I remember correctly. I don't have the cooling redundancy to support it.

Dave

[RICK LAKE]

Undy with this spike problem I would first go out and get a infrared temp gun. Start the car and watch the temp readings. It could be the gauge, sendor or a grounding problem to the block or if you have teflon tape rapped around the threads to seal the coolant it could cause a poor ground until thing heatup. At 250 there should be steam and water boiling coming from your tank outlet. If not than something is giving bad readings. Are your gauges electric or manual with a solid tube coming from the sendor to the gauge. How much pressure is on the coolant system before the temp drops? I know I am reaching but, who put the motor together and is it possible they installed a head gasket on wrong. This has happend more than once. The headgasket should look both the same with the ends of the gasket sticking out, if not, possible head gasket in upside down. Motor will run but get hot over a long drive. 1 hour or more. For the $15.00 dollars go to the pepboys and look for the themostat old style for a dodge 383-440. look at the outlet, it's a 1/2" larger than the FE one. Trim the out side edge to fit in the opening of your intake manifold and twick the 2 top supports to fit in your tank. Drill the holes. This should work. Is the motor new and tight? how many miles on it since assembly. Rick L. I only use tap water and 2 bottles of water wetter in my car. My coolant recover kit sucks down the whole system so I get no air pockets. Good luck. Rick L.

[undy]

I actually have 2 or 3 infrared guns laying around.. I'm a HVAC contractor and have quite a bit of knowledge of heat rejection etc.. I use them on the Cobra all the time (checking individual header primary temps helps with adjusting 4 corner Holleys and Barry Grant carbs)

The temp gauge appears to be operating correctly all the rest of the time so I suspect it's working correctly when it's reading 250 deg. There's no potential difference from the sending unit's housing to ground too (good ground contact). It's conceivable that there's a 250 deg pocket of steam flowing past the sending unit while the rest of the system's not up to temp. That would account for the disparity between the gauge reading and the "feel" of the intake. I'm thinking (hoping) that the 4ea 1/4" holes will take care of the steam pockets. If they don't then I need to rethink my problem solving tree and look elsewhere for the problem/solution.. I'm banking that's not the case. The head gaskets are fine (I assembled). If they weren't I'd be overheating all the time. The gauges are electric, not cap tube. All the Robertshaw (Milodon and Mr. Gasket) high flow thermostats (BB Chrysler and the smaller current style) have the same diameter openings, so there's no advantage there as I'm using the Robertshaw now. I'm running Water wetter too. You need to stay away from tap water (I used distilled water) as it contains too many conductive minerals which promote galvanic corrosion and electrolitic activity.

Coolant recovery kit??

Thanks for the help/suggestions,
Dave

[undy]

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