What's the best way to refill empty Twin Cam cooling system?

[Sea Ranch]

Greetings,

Wondering what your ideas are. I like the vacuum system (like the UView Airlift) but a little pricey.

What have you found that works? What is the best way to get the system full with no air, or as little as possible?

Thanks!

Randy

[StressCraxx]

Drill a 1/8" hole in the thermostat.

Use distilled water with the antifreeze. Open the heater valve. Fill the system slowly. Warm up the engine, look for leaks. Drive it. Top it up after it cools.

Have fun!

Dan

[Sea Ranch]

Thanks, Dan.

The thermostat I'm using doesn't have a bleed hole, so I wondered about drilling one. The idea there is that as you fill, even with the engine cold, some coolant can get past the thermostat into the engine block?

This is a newly rebuilt engine, hasn't been started yet. Is there any way of getting coolant into the engine block before I actually fire it up for the first time??

[MarkDa]

I've never really seen filling engines of any type a particularly big deal.
It is a good idea to have a thermostat that allows air through so the system has a chance to get reasonably full before starting the engine.
So yes drill one.
It does help to get the rad cap to be the highest point though. I'm lucky that I can do this on my drive but one can jam a tube or cut off plastic bottle into the top of the radiator to extend it.
So after initial filling I just start the engine and top up as needed.
The heater is inside the thermostat so providing there's a way air can get past the thermostat it'll fill quickly enough.
Tickover is enough to release most of the air.
You don't have to get it completely full, so long as the overflow bottle has coolant in it the cooling of residual air in the header tank will draw coolant back into the system and top it up.
The most important thing is having a back flow radiator cap that seals well on the cap itself to ensure refilling on cooling .

[Orsom Weels]

Thanks, Dan.

The thermostat I'm using doesn't have a bleed hole, so I wondered about drilling one. The idea there is that as you fill, even with the engine cold, some coolant can get past the thermostat into the engine block?

This is a newly rebuilt engine, hasn't been started yet. Is there any way of getting coolant into the engine block before I actually fire it up for the first time??

The idea of the bleed hole in the thermostat is to let air out rather than coolant in. As you fill the radiator, coolant will flow into the block via the bottom hose & through the water pump. Air will then be forced out through the bleed hole, the top hose & escape through the radiator header tank & filler neck. Coolant will also fill the heater from the from the lower hose connection in the water pump stub & air will be forced out via the other hose connection at the thermostat housing, through the thermostat bleed hole in the same way. If there is no bleed hole in the thermostat, air can't escape & that's when you get troubled with air locks.
As Mark says, parking/jacking the car with the nose high will help, but using an extension tube in the rad filler can impede the escaping air if it becomes filled with coolant, so if using this method, fill slowly & always make sure the air can escape.

Regards, Tim

[Sea Ranch]

Tim, thanks for the reminder on the direction of the fill. Got it.

I have read somewhere that the relief hole in the thermostat is supposed to face a certain direction, but I can't see why or how that would matter.

[rgh0]

The hole both helps removal of air from the system when filling from cold as well as helping the thermostat to open at the right time by allowing a small flow of coolant past the thermostat so a pocket of cold water does not build up behind it a slow its opening.

I don't believe there is any reason to orient the hole in any particular direction when locating the thermostat but having it on the outside of the thermostat holder casting would ensure the thermostat has the maximum exposure to water as it flows through the hole during warm-up but I don't think this is critical

cheers
Rohan

[richardcox_lotus]

From memory, I read the hole should be oriented to be between the thermostat & top main hose, leading to the top rad inlet.

Can?t remember why though!

Regards
Richard

[rgh0]

From memory, I read the hole should be oriented to be between the thermostat & top main hose, leading to the top rad inlet.

Can?t remember why though!

Regards
Richard

Probably similar rational to mine but I am sure it is not really critical

cheers
Rohan

[MarkDa]

If one's cooling system is so marginal that this bleed hole alignment is important then I suspect there are bigger issues to address!
Having said that some cars have vertical thermostat where having the hole at the top obviously let's 'all' the air through at initial filling.

[Bigbaldybloke]

I?m about to fill my cooling system from completely empty so am interested in this topic, what is the capacity of a completely empty cooling system on the Plus 2?
Knowing this would give a good idea of whether there was a big airlock that needed clearing.