3VZ strange overheating issue just

[briweekes]

No other cooling issues, it was just not efficient with the pipe going over the top of the engine and a high point there. Coolant circulation seems better now. No funny angle. This was tested. By thrillseeker using transparent marine hose, which revealed air accumulating at the top of that arc, and not being able to be bled out.

[Paul Woods]

Then the pipe had the wrong angle on it which made it higher than the filler point, if the filler is the highest point then you don't need any extra bleed points.

[cdwood2010]

Looking at most 3vz builds (and mine) people use either a regular aftermarket hose or the original Camry top hose. It has a habit of sitting a bit hunched.

I've noticed Paul uses a slightly different hose with a lower profile so this isn't an issue.

I generally fill up the coolant with a pop bottle hopper - basically a pop bottle made into a funnel with the top thread wrapped in masking tape so that it seals. That way you can give the top hose a bloody good squeeze and get all the air out, then cap on. Never had an issue once its bled fully, but I have seen air trapped as Brian describes.

[Paul Woods]

I guess my point is even if you had that top hose with a small airlock in it, that isn't going to matter and will eventually be forced out, the filler neck is still the highest point in the bay and air will always find its way there.

Mr2 cooling systems are self topping up once you have the inital burping done, the pressure cap acts like a tidal gate.

When running it should never open unless there is a problem.
On shutdown the pressure builds in the engine and the cap opens forcing coolant into the expansion bottle.
When cool the engine now creates a vacuum, which sucks coolant back out of the bottle back into the engine via the cap which allows return under those conditions.

So all trapped air will eventually find its way to the bottle.

Extra bleed points are simply not needed.

[cdwood2010]

Um, I always thought the expansion bottle was just for expansion, didn't think it could draw coolant back through a one way valve.

I generally just bleed them lots and leave the hopper full overnight. It gravity eventually gurgles it into the system.

[Paul Woods]

The coolant pressure cap is a two way street, it flows both ways, out under pressure, in under vacuum.

[cdwood2010]

[Paul Woods]

If you notice the pipe leading from filler point to expansion cap it goes to the tube that is submerged in the bottle, so it is never allowed to suck air back in, only coolant, so the system works like the tide flowing to and from the bottle on shutdowns.

People see problems from piping to the wrong outlet of the expansion cap, using the overflow as the feed, so what happens is the engine chucks coolant out on shutdown but during the cooldown period draws air back in, this gives an almost head gasket failed symptom, same thing happens on Mk1s with the original white plastic caps that crack, although plumbed properly it draws air back in during cooldown. The later Mk2 black plastic caps do not crack and never see the issue.

But yes, essentially extra bleeds, although not doing any harm, are not needed on V6 swaps.

[cdwood2010]

okay, I still don't understand how a pressurised cap, requiring 0.9 bar or whatever to open, can open and suck coolant back in.

The pipe to the expansion bottle sits above the spring cap seal, so certainly pressure (>0.9 bar for example) makes it open and expand, but how does it open to draw coolant back in again?

[Paul Woods]

It's witchcraft, and i've no clue what i'm talking about.

http://auto.howstuffworks.com/cooling-system7.htm