Thermostat bleed hole importance?

[EcoCivic]

As the title says, I'm wondering how important the thermostat's little bleed hole is. From my understanding, its purpose is just to allow a tiny bit of coolant circulation all the time to make the initial fill easier and prevent problems when the cooling system isn't refilled properly.

Since I always use my spill free funnel when adding coolant and let the engine run at varying RPMs until the thermostat opens and then until there is no air left, would it be safe to block off the bleed hole for a little faster warmup and more stable temps in cold weather? Possibly even slightly better block heater performance and a slower cool down since a thermosyphon through the radiator would be prevented?

I would normally just try something like this and see what happens, but the thermostat I'd be trying this on just cost me nearly $100 and that was a deal, so I'd rather not destroy it.

I'm thinking not having a bleed hole should be safe since the system will be completely bled before the car is driven and air should pass through an open thermostat no problem, but any input would be appreciated!

[freebeard]

I don't know the answer, but there may be other ways of achieving the same goal. Paint the engine block with insulative paint?

[EcoCivic]

Originally Posted by freebeard

I don't know the answer, but there may be other ways of achieving the same goal. Paint the engine block with insulative paint?

There are definitely other ways of achieving the same result, but I never heard of insulating paint.

That method would have the downside of somewhat decreasing cooling efficiency all the time though. Although the engine is liquid cooled, the surface area of the block, head, oil pan, valve covers, etc somewhat contributes too, especially to oil cooling.

[freebeard]

Insulative paints have microscopic vacuum beds. There're also intumescent paints that expand and char when expose to flame. Different application.

Too bad one can't use engine heat to warm the transmission to operating temps.

[Piwoslaw]

IIRC the bleed hole is not just to de-air the system, but also to ensure the thermostat is not sitting in stagnant coolant, ie it is "up to date" with the current temperature of the engine?

Modern cars have sensora all over the engine and a heating element in the t-stat housing to open it when the ECU wants to, but those also should have a bleed hole as mechanical back-up.

[aerohead]

I vote: 'leave it alone!'
When it's open, it's an industry leader in hydrodynamic efficiency.
The entire cooling system design is predicated upon the thermostat's architecture exactly as it is, transporting a miniscule amount of coolant at cold-start, and turbulent 'blending' of the solution throughout the cooling system, to produce an 'average' coolant temperature as 'seen' by the ECU's sensor suite during open-loop operation.

[hayden55]

Are you talking about the thermostat bypass port or the bleed port?
1. is just a high spot for initial bleed.
2. is the circulation port for the thermostat that allows coolant to circulate until the thermostat opens.

[EcoCivic]

Originally Posted by Piwoslaw

IIRC the bleed hole is not just to de-air the system, but also to ensure the thermostat is not sitting in stagnant coolant, ie it is "up to date" with the current temperature of the engine?

Modern cars have sensora all over the engine and a heating element in the t-stat housing to open it when the ECU wants to, but those also should have a bleed hole as mechanical back-up.

Great point! On some engines, I could see that being an issue. However, on the K series, the coolant bypass goes through the thermostat housing and continuously circulates coolant over the thermostat.

On something without continuous coolant circulation around the thermostat, I could see that being a major issue.

Anyways, I decided to block off the bypass hole this afternoon with a nut and screw and a little JB Weld around the head of the screw and on the threads to fully seal it and make sure it can't come loose. The thermostat is now completely sealed and no coolant can get through or around it while it's closed.

I plan on installing the new modded thermostat tomorrow and will report back with the results.