Drilling the thermostat??
 

I've done away with my cooling water bypass line that ran from the intake to the water pump suction, common to all FEs. It's been plugged on both ends for some time now. I've never bothered (should have) to drill the thermostat to maintain flow across the engine when the thermostat is shut. For not doing this, I've suffered some time now with high coolant temperature spikes prior to the thermostat opening. Convection, not flow, getting the hot coolant to the thermostat's thermo bulb takes too long, hence the temp spikes.

The solutions to this are four fold, take the thermostat out, install a restrictor plate in place of thermostat, reinstall the coolant bypass or drill some holes in the thermostat. While not going into the merits and draw-backs of each, I chose to drill the thermostat. My question is, how many and what size holes do you guys recommend?? I've Googled my arse off on the subject and what I've found has led me to 2ea 3/16" holes.

BTW... I'm running the Robertshaw high flow/balanced t-stat, which I'll drill the "balance cup" that actually opens, not try to fit the holes in the perimeter ring. The thermostat is also marketed by Milodon and Mr. Gasket, all the same t-stat.


Just in case you're wondering .... why?? The factory bypass actually recircs the water through the block, bypassing the radiator. This facilitates a quicker reheat at the loss of a small amount of engine cooling. While this does not present a problem with the average vehicle (due to designed massive cooling system capacity redundancy), this good be the proverbial straw that broke the cooling system's back with our "cooling system challenged" Cobras.

Undy: You must drill the thermostat to allow water to circulate slowly as the engine is warming up. This way the coolant is warming evenly as is the engine. Otherwise the engine will have very hot spots and flash into steam while others areas will be cold. That's the reason for the bypass in the first place. You're seeing spikes in engine temps because the localized steam expands and blows open the thermostat. When the superheated coolant then passes the thermostat and the water-temp sender, you see a spike in engine temperatures followed by a rapid cooling.

See ERA's instructions on drilling a thermostat and how to position it in the housing: Thermostat modifications

I drilled my thermostat as ERA recommended but for the added benefit of bleeding the air that gets trapped in the intake when initially filling the system.
I understood that the bypass line was plugged in the cobras because the radiator was so far away.

Impeller Cavitation
 

The bypass hose also helps prevent cavitation of your water pump's impeller. If you plug it, the "one-hole" ERA method might not be enough flow -- either use the four hole Gessford Method, pictured below, or keep the bypass hose unplugged (I keep the bypass hose unplugged and use the ERA method).

http://www.gessford.com/cobraparts/Thermostat-08254.JPG

The single hole in the thermostat serves an additional function besides bleeding air through.
It allows a small amount of hot water to bypass so that the thermostat is efficiently "bathed" in coolant. Without flow, the thermostat won't respond until much later. Since the thermostat will open in a timely fashion, I don't feel that the other holes are required.

One of the holes should be at the top when installed, because the air bubble congregate there.

Actually, I would forget the holes and use the bypass hose. The Ford engineers do not just add stuff to make engines more expensive. They added the bypass for many reasons.

Yep, and now that most of our water is fluoridated the risk of cavitation is greatly reduced. :rolleyes::D

As far as I know, only Ford has these bypass hoses. I have never seen them on Chevy, Chrysler, Pontiac, Olds, Buick, Tucker, Kaiser, Nash, etc., etc.

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A lot of cars have internal bypass channels in the water pump itself, small block Chevys come to mind. Our friendly FEs do not.

EDIT -- Looks like Mopar saw the light in 1951. **NEW** NAPA Airtex Water Pump

The 351C, 351M and 400 engines have internal bypasses, too . . . in the blocks.

I know this is refrenced to FE's however:

I find this challenging when using Webers on a 289 smallblock with dual manifold outlet instead of the normal (manifold contained) provision for a 180 degree thermostat (no provision for bypass). I have a thermostat in the hose before the radiator. It has (2) 3/16 holes. It seems like it takes considerably longer to warm up than before I installed the Webers, previously it had a Holley 650 D/P. My observation is that when it approaches the 180 temp of the thermostat and it begins to open, the indicated water temp drops considerably from the surge of cool water from the radiator and causes the thermostat to close. The engine is VERY slow to get to temp even at road speed and never reaches the previous (with 4 bbl) operating temp. I am using the Fluidyne Shelby spec radiator.

Drill the holes.
Without a bypass you need the holes....for all the reasons already given.

The question wasn't whether to or not to drill the holes. As I'd said I was already going to do that. The questions were, How many holes and what size?:confused:

thanks for everyone's input.

Dave

With a functioning bypass hose a single quarter inch hole at 12 o'clock will do. If you are blocking your bypass hose use four quarter inch holes.

What pulleys are you running?
 

Undy I have 1 3/16" hole in my thermostat. I am also using Dodge thermostat The outlet is 1/2" larger than the FE one. You where talking about spikes with coolant temp. I am running a shelby 482 motor and the heatup is quick for coolant, 2-3 minutes, the oil takes about 5-7 minutes. The thermostat is a 180. I had a overheat problem and spike temps, I changed everything. The biggest change was getting rid of overdrive pulleys. I had the March setup. They provided just enough flow to keep from hitting 225 when roadcourse racing. I limit the run to 5 laps. I am now running custom pulleys that are 5 1/2" crank and 5 3/4" waterpump. The temp after racing is in the 190's I still get the temp spike in the 190's until the thermostat opens but I get a drop to the 160's quick and after a couple minutes of driving the coolant is stable a 180-185 with the motor at idle. March makes a nice pulley kit for FE's and on the street they get by as long as you are not in a stand still for a long period of time. The under drive is about 20-25%, and IMO thats too much. ASP built my custom pulleys. I do have the bypass hose on and working. The dodge thermostat does out flow the FE one by alot. If you go to an autozone of pepboys and look at the back where the outlets are you can seen the differents. The only thing is you need to remove 2mm on the edge to fit in the stock location on the manifold. Like said before hole goes on top for air. Hope this helps Rick L.

Rick,

Are you running the pump bypass or is it hooked up? I might have missed it in your responses.. IMO, I need to drill enough holes to give me the approximate volume that the bypass line had. I would assume that's a Ford designed predetermined flow that's required. No way one or two 1/8" to 1/4" hole will give you that. It looks like Gessford had already figured that out. Given the ID of the bypass hose I would think, as in Patrick's post, that 4ea 1/4" holes would approximate the volume of the bypass hose. I can calculate it closer mathematically too. Overheating isn't a problem. My pulleys are of the right diameters. The only problem is the intitial temperature spike before the t-stat starts to modulate.
dave

FWIW, I have the bypass hooked up and have my t-stat drilled as Gessford suggested- works great with no problems at all.

After 12000 miles with bypass blocked off and one 1/8 hole drilled in thermostat...runs just fine.

Holes in thermostats are not there to replace the bypass, but rather to let any air trapped in the top of the water jacket escape. Coolant that leaves via the thermostat heads back to the radiator and is replaced by cold coolant. Water entering the engine via the bypass is warmer and allows the block to attain a more consistent temperature.

Just my $0.02

Bob

Correct Bob, except when there's no bypass. Then you need a bigger hole.:LOL: