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That is the idea: The bubbles will circulate into the bottle and get trapped. However, if you have a big enough bubble, then it won't circulate. It will just hang out in an upper volume. That can be really bad if it is in the head or the radiator. If you get a large enough bubble in the head, then local boiling will occur and the steam pressure will block circulation.
 

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'00 MR2 Spyder, base model
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Discussion Starter #22
So a bunch of smaller air bubbles can group together to cause a larger pocket. Can you cavitate the water pump in such a case? burn it out?
 

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I've done a few coolant changes and here is what I would recommend:

Drain from the front and rear. (not the middle, risk of damage to the coolant lines)
Jack up the front of the car to get the remaining coolant out from the rear.
Re-fill coolant, with the rear drivers side of the car on a jack stand.
Start the car, reach operating temp, top off coolant.
Let the car sit overnight with the coolant fill cap off (still on the 1 jack stand), run to operating temp and top off coolant again.

The service manual instructions were fine when the car was new and you were a dealer service tech with the car on a lift. The cars are old now and gravity is free. Use OEM toyota coolant. I've never had any overheating, water pump or hose failures after all these miles.
 
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No way .... if he keeps going at the same rate he'll have a little over 112k in 10 years . Then maybe I'd think about it , maybe . Working under your theory he should change out the radiator , cooling fans and probably a serpentine belt .
I might agree about the water pump, but all of the rubber parts degrade with time, not just miles.
 

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I've done a few coolant changes and here is what I would recommend:

Drain from the front and rear. (not the middle, risk of damage to the coolant lines)
Jack up the front of the car to get the remaining coolant out from the rear.
Re-fill coolant, with the rear drivers side of the car on a jack stand.
Start the car, reach operating temp, top off coolant.
Let the car sit overnight with the coolant fill cap off (still on the 1 jack stand), run to operating temp and top off coolant again.

The service manual instructions were fine when the car was new and you were a dealer service tech with the car on a lift. The cars are old now and gravity is free. Use OEM toyota coolant. I've never had any overheating, water pump or hose failures after all these miles.
Why not just follow the proven method of refilling as stated in the shop manual? You don't even need to start the engine, just realize it can take a half-hour to fill and purge. Follow the shop manual procedure and it works perfectly every time and you will not have to worry about any large bubbles of air being trapped. I also disagree about you draining idea. It is much more effective to use the intended drains than removing the lower radiator hose.

Dave
 

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'00 MR2 Spyder, base model
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Discussion Starter #26
the two coolant line drains seem to be the lowest point on the system, and the logical way to get most of the fluid out. I haven't read of anyone messing up the coolant lines doing this change. Unless you over tighten them?
Thanks everyone.
For anyone who has already done this, does any fluid come out of the the engine drain if opened? Or is it to let air into the system to make the draining quicker?
 

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The block petcock valve is under the #4 exhaust pipe about midway on the block.

I would follow the BGB regardless of the age of the car. Personally I would use wire spring clamps like OEM if I were to change the hoses. I have thought about changing all the hoses but for now they are still in good condition. When I have a problem with one hose they will all probably be replaced.
 

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I love those "how does it?" questions the most.
First off to level the field let's call your overflow my "expansion tank" for starters.
Coolant expands into the bottom and contracts (creates a vacuum) when cool and is sucked back into the system, like covid magic.

Your expansion tank is not meant to deal with air at all. Period.

BGB procedures are there for a reason, they work.

BTW if your operating with 25 year old rubber coolant hoses I'd think before a pressure test that a "mechanic" swears will show you a leaker.
Here's the mark1 thermo bleeder. Bleeder valves, thermostat.jpg
78929
Bleeder valves, thermostat.jpg
THE BLEEDER IS FLAWED IN THAT THE CRUCIAL ITEM IS WEAK PLASTIC.
HOWEVER, THAT ENGINE DRAIN PETCOCK HAS THE SAME THREAD AND IS ALL METAL AND CAN BE USED WITH SMALL SOCKETS.
 

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I love those "how does it?" questions the most.
First off to level the field let's call your overflow my "expansion tank" for starters.
Coolant expands into the bottom and contracts (creates a vacuum) when cool and is sucked back into the system, like covid magic.
Mister Tim, I have to remind you again that we are talking about an entirely different car here, with an entirely different cooling system than you are familiar with. The spyder has a closed, two phase cooling system and no expansion tank at all. AND THERE IS NO TIMING BELT. :oops: :rolleyes::oops::LOL::ROFLMAO:
 

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Just to be clear: the Spyder's fill tank is also known in the industry as a hot-bottle and definitely is supposed to have pure liquid in the lower half and air in the top. It's function is both to handle thermal expansion in the system and also to continually de-aerate the system. That is why there are small hoses going to and from the bottle. Coolant, air bubbles and steam go in the top, and only liquid coolant returns to the engine through the bottom hose. It is not an overflow tank, though if you replace the OEM tank with aftermarket, you can add one to it.

Dave
 
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