mikuni

Sheepers' RA28 Celica

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While the coolant is out, is it worth poking a snake camera up its passages to look for blockages/forgotten rags etc?

I have one if that's any use  

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Hang on a second! super dumb question... do you have the rad plumbing the right way? Water pump suction to bottom of rad and thermost to top? 

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yea so the thing i welded up was a threaded hole where a gauge sender went.

the only part of the water circuit that i have changed is the hot water feed to the throttle body which is now blocked. it was a 6mm pipe.

 

also the UZ has the thermostat in the return line sort of. its fed hot water at the back of it from the water bridge between the heads and as it opens it blocks a bypass hole with a flange at the back. so technically the thermostat is in the return line but its kind of not. 

the head gaskets have bigger water holes on one head than they do on the other and im assuming thats done to force flow across from one head to the other at the back water bridge.

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What is it with toyota's and cooling system airlocks? My 2f was the same, had to burb it with the front way up and even then it would still get an airlock.. 

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Do you have old themostat you could butcher so it closes the bypass but has full flow from the radiator? 

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This sounds pretty similar to what an AW11 does when you don't bleed them properly and get an air lock. Everything seems OK at first, then the temp shoots up and water boils in the head. 

Sometimes you'd get a hotspot so bad that when the water got there, it would instantly boil and squirt a litre of hot water out of the radiator filler hole.... The solution was usually to force feed water into every cavity (remove rad hoses and squirt water directly into the radiator, same deal with the heater core), then open up all 3 sets of bleeders and run the car for at least an hour until all the air bled out. Once it was burped properly, it was good.

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You've changed rods / pistons from 10.5 to 9 CR, yeah? What does that do to the combustion? Maybe the flame front is slower, so it all needs more advance? As Cletus mentions above, over-retarded ignition can cause overheating? (I'm pretty sure I've seen that on -cough- smaller engines). I'm also reading reports on other engines over-heating when too retarded. 1st graph here has some clues miiiight be helpful. https://www.sciencedirect.com/topics/engineering/compression-ratio 

To my eyes it looks like the r8.6 peak pressure is lower, but also takes longer to come up.

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21 hours ago, Truenotch said:

This sounds pretty similar to what an AW11 does when you don't bleed them properly and get an air lock. Everything seems OK at first, then the temp shoots up and water boils in the head. 

Sometimes you'd get a hotspot so bad that when the water got there, it would instantly boil and squirt a litre of hot water out of the radiator filler hole.... The solution was usually to force feed water into every cavity (remove rad hoses and squirt water directly into the radiator, same deal with the heater core), then open up all 3 sets of bleeders and run the car for at least an hour until all the air bled out. Once it was burped properly, it was good.

 

Vacuum fill kits on trademe aren't badly priced:

https://www.trademe.co.nz/motors/car-parts-accessories/tools-repair-kits/repair-kits/listing-2534612104.htm?rsqid=208f7d2cbf5348d8b555dd4f1c58d5ad-001

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I'll second Vacuum filling cooling systems, once you've done it that way you'll never wanna go back. Eliminates all doubt.

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When you were putting on the new manifold, etc.  Did you have pieces of cloth or tape covering ports, etc. or something similar that may have accidentally been left on?  

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Is there a way you flow check the engine, I guess there won't be any data on flow rates but you might get an idea on how much water is passing through the heads etc

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How are you measuring the heat?

You mentioned something about taking out a gauge sender, was it relocated? 

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Coming from left field here, but has the diameter of your water pump drive pulley changed ?

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10 hours ago, thegreatestben said:

You have me convinced, can get them for $55 delivered here https://www.trademe.co.nz/motors/car-parts-accessories/tools-repair-kits/meters-testers/listing-2536401264.htm?rsqid=ce804657b5744d91b11083a2d3c0e32a-001 haven't used it so not a recommendation as such. Same price as AliExpress without the super long current wait.

Posting incase Sheepers wants one / doesn't have one.

 

Sounds like a right cnut of a problem, hope you suss it soon!

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Yeah could well be actually, i'm willing to take the chance when it's $90 cheaper with shipping. If it breaks, we fix it, with have the technology. Sheepers can probably fab one up to put them both to shame anyway.

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Is your temp gauge reliable?

My LT1 motor into a VN commodore conversion had massive overheating issues, I did everything you could think of and couldn't solve the problem... 

Then out of desperation I purchased a cheap temp gauge from repco and hooked it up.  Yeah...turns out I was trying to solve a problem that didn't exist. It was the original temp gauge that was the problem.

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