Wot! No Bleeding Screws?

Honest John Back Room » Technical matters
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Tue 15 Oct 2002 22:16
Wot! No Bleeding Screws? - Rich Mixture
In every vehicle I've ever owned or worked on there have always been bleedscrews in the cooling system (usually in the heater exit pipes and maybe the top hose feed to the water pump as well) to assist you in bleeding all the air from the system when replacing coolant.

I've just bought a 1990 Toyota Corolla for SHMBO and am about to change the oil and coolant as a precaution. Checking both the vehicle and the Haynes manual I find no mention of bleedscrews. Haynes just tells me to drain and refill the system.

Question - What wonders of hydraulics have Toyota used to achieve this? Is it likely to be this simple or am I still at risk of airlocking with this vehicle? Should I refill the rad very slowly? Any other tips/hints/help welcome.

Thanks

RM
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Tue 15 Oct 2002 23:02
Wot! No Bleeding Screws? - Dynamic Dave
None of my previous Vauxhall's (starting with a Mk1 Astra) have ever had bleed screws. I've always just drained and refilled. However, what I do is leave the cap off the expansion tank after the first initial fill, run the engine and then top it up as necessary. I then check the next day when the system is cool again. Never had any probs with air locks.
Not sure what age of vehicles you're used to working on, but what you have to remember is that there is always a certain amount of air in the expansion tank anyway. Any air in the system will normally end up back there.
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Wed 16 Oct 2002 10:03
Wot! No Bleeding Screws? - Claude
I have owned (and serviced) 19 cars and never come across a bleed screw in a cooling system !
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Wed 16 Oct 2002 10:34
Wot! No Bleeding Screws? - keithb
I have owned (and serviced) 19 cars and never come across
a bleed screw in a cooling system !

I would have said the same until I worked on French cars. I have seen bleed screws on Renault & Citroen cars but never on other makes. The French cars also had rather lengthy and specific methods of refilling.
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Wed 16 Oct 2002 11:16
Wot! No Bleeding Screws? - Rich Mixture
Interesting. Yes - They've all been Peugeot's, Renault's and Citroen's. Bleedscrews are obviously peculiar to Gallic voitures although I hadn't realized this before now. Perhaps David W might care to comment?

Thanks all for your responses...

RM
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Wed 16 Oct 2002 12:55
Wot! No Bleeding Screws? - Humpy
I think...........
Because the expansion tanks are above the rest of the cooling system there shouldn't be a problem with airlocks. With the french cars often the expansion tank (sometimes included with the radiator) is below the highest point of the system causing the likelihood of airlocks and the need for bleeding screws. Does that sound plausible!!
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Wed 16 Oct 2002 18:38
Wot! No Bleeding Screws? - keithb
I think you're correct. On my son's first car - an old Renault 5 - you had to unstrap a glass bottle (expansion tank), undo 3 or 4 bleed screws, hold the bottle up high while filling it and close each bleed screw as coolant appeared, all the while trying not to drop the glass bottle. Other areas of the car were also designed to make maintenance as difficult as possible and I vowed never to buy a Renault.
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Wed 16 Oct 2002 19:54
Wot! No Bleeding Screws? - Doc
Rover Metros have 2 bleed screws; one on the heater flow pipe and one on the main return hose.
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Wed 16 Oct 2002 20:06
Wot! No Bleeding Screws? - madf
Peugeot 10 has 2 bleed screws : on at water pump and one on heater pipe. Expansion tank is above the level of both. No Ford has any that I know of .

The Pegeot has also a reputation for bursting hoses: the design of the bleed screw is a rubber screw thread bonded to a hose .. which fails after 5 years at a cost of £35 to replace (parts only.. takes about 1 hour after you have removed all the shields, rusted stupid clips which have to be replaced etc). Typical French design to increase the revenues from spare parts.
Of course the hose is also kinked to provide an airlock just where the screw is ..

Now that is what I call perverse design.. just plain bad engineering.. unless it is to increase the sales of spares which are unique to Peugeot..

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Wed 16 Oct 2002 20:06
Wot! No Bleeding Screws? - madf
sorry should read Peugeot 106
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