You're somewhat correct.. except:

Water doesn't enter the engine via the bypass, it leaves the engine. The thermostat IN ADDITION to venting entrapped air/steam pockets can do double duty. It can TOTALLY provide the required engine coolant flow movement through the engine when the coolant bypass is done away with. This coolant flow through the bypass has nothing to do with attaining a more consistent temperature as its designed use is solely for a quicker engine warm-up (that amount of coolant bypasses the radiator). If you size and have the required amount of holes in the thermostat in conjunction with a blocked bypass then all that water that bypasses the radiator now flows though it. That gives you a "tad" more cooling capacity, which is valued to many big block, large cubic inch Cobra owners. The minus part of the equation is that engine warm-up suffers somewhat, not a big deal with me. The big thing you've got to worry about is too many and too large holes. Then the engine, on cooler days, may not come up to temperature.. Not a good thing.


BTW.. The cross-sectional area of a 1/2" (ID) coolant bypass hose and 4ea 1/4" drilled holes is the same, down to a hundredth of a square inch.. Flow should be approximately the same, save some unknown variables.


Dave

I do have my bypass hooked up
 

Undy I do have my bypass hooked up. Any motor is going to spike temp until the spring on the thermostat gets weak and lets the flow of coolant go through the housing. As long as you are not hitting 220 temp don't worry about it. My temp gauge is like a yo-yo until it stabilizes. 200 -160 in 3 seconds. Until all the coolant is within 10-15 degrees of your temp spec on the thermostat housing you are going to get spikes. The problem with my car was worse with the underdriven pulleys. I am sure the Gessford thermostat works perfect with the 4 holes. I would think that mounting it with the holes at 12 & 6 would help remove all air in the system if you don't have a vacuum pump to use on the coolant system. I used this the last time It's works great. My march pulleys where underdrive, My fault on that info. Also run a edelbrock waterpump with the shield that is riveted to the impellor for more flow. Rick L.

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!:CRY:

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...

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.

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

Infrared thermometer to start
 

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.

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

last post didn't show up??:confused:

coolant transfer machine
 

Undy He have a coolant flush and fluid transfer machine that removes the coolant after run to operating temps. Vacuums the whole system down and replaces with new coolant. The vacuum parts keeps air pockets and air from being caught inpockets in the heads. Have you tryed to purge the coolant system with the motor on the first startup cycle? The best place would to be at the highest point of the coolant system on the motor. I would try cracking the sensor and see if coolant leaks out or air. If air, you may have to do this 4-5 times to purge the system. LS1 motor have this problem. It's possible to have 1 head gasket in wrong on the FE and run the motor for over 1 hour and just start to overheat. I know I mounted one wrong. Motor ran fine. but over an hour the temp was at 220 with a 180 thermostat. Plenty of flow of coolant but running hot. Try the holes, IMO I think you are going to push too much coolant through the thermostat housing without letting it heatup. It may fix the spike problem but might hurt the effectiveness of the coolant system. Dave I will get you the right number of STAT tomorrow for the thermostat with the larger opening. You must have alot of air in that motor that after 5-10 drives and till having this problem. I wonder if you have a head gasket not sealing, and it is bleeding compression gas into the coolant system. Motor heats up and the expansion is stopping the leak. Motor cools off and you have the air in the system again. What combo are you running, iron block aluminium heads, iron heads aluminium intake, all aluminium?? You have a recovery bottle so the hot coolant goes in there and when the motor cools off it is sucking coolant back into the motor but not all. There is a tester kit for checking combustion gases in the coolant system. Rick L. Ps used to drive on VA beach in the 70's, there was a patrol guy on the beach in the summer with a black jeep still there? I lost $50.00 to him in a drag race on the beach at 2:00a.m. Still a great beach for the sites.

I don't run the bypass. I drilled three 3/16 holes in the thermostat. It does take a bit longer to warm up. I copied what Stewart does with their thermostats where no bypass is used.

Stewart Components - High Performance Automotive Cooling

Rick,

I'm running the Pond 482, all aluminum. It's not and air entrapment problem as all other times, other than the intial temp spike, the temps are dead nutz on (between 180 to 185). I can, even after a long (hard) drive, let the car sit and idle in 80deg weather and the thermostat will modulate open and closed to maintain 180 deg. I let it set running like that for 30 minutes w/no increase in temps. Air inthe system is not aproblem. I did the "wrong side up" on the head gaskets on a 428 I built so I know the head gasket dilema, not an issue here. I'm about as sure as I can be that it's just too low flow through the engine w/the t-stat closed, stem pockets and the whole mess. Afret, I bought another t-stat, talked to Stewart Componants Technical, and have drilled 4ea 1/4" holes. I'll install today and report back on the findings.

btw, fyi.. I've a AAS in Automotive Technology and a "not-current" master ASE cert.. so... pretty heavy w/theory etc. knowledge.. It's Just a hobby though .. as HVAC pays much better here.:LOL:

Yea, Va beach is the shiznits during the summer. The co-ed Russian babes are here all over the place, dressed in minimal garb.:eek::D**) ...and eager to dive head-long into Capitalism

UNDY, How did your 4 holes turn out?

I did the 4ea 1/4" holes and they worked fine ... well ... they worked too good. I drove it a couple times in 50+ deg weather and I had problems building enough engine coolant temp. I was wondering if that was going to be an issue. I bought another thermostat (my 5th Mr. Gasket stat I bought and modified, I'll get it right yet;) ) and I'm going to do the 3ea 3/16" holes on this one, per Stewart Componant's recommendation and post results.

The short answer though is yes, it did eliminate the high temp spikes prior to the thermostat opening.

Dave

I think 4, 1/4 holes are way too much, I have 4, 3/16 holes in my street car and race car and it works just fine.........

David

Undy, I've forgotten now -- do you run the bypass hose or do you not?

No, hence the need for tstat bypass holes..