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The overheating probelm that has baffled the Zed Shed


laidbackluke

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Evening all,

 

right we have a quite a doosie for you guys.

 

as you may all know buster and keyser being the heroes that they are very kindly fixed up my car and got me back on the road before Xmas.

 

A few weeks ago however, one of the coolant hoses popped off (the small on located to the left of the plenum, tucked behind the larger one) it looked to be just because the clip wasn't quite secure, anyhoo, i popped it back on, topped up the water and away i went.

 

Since this though the car has been overheating, the boys put it down to an air lock and bled the system only for the same thing to happen again...and again :(

 

last Sunday the Zed Shed took a little road trip out to Dorchester to try and solve the problem, we took out the thermostat to find it was pretty worn, so to get me on the road again without overheating removed the thermostat.

 

now is where it gets annoying....

 

 

After testing a spare thermostat to ensure it was working we fitted it back into the car. When ticking over its fine, nice and warm in the cabin and the temp gauge is sat normally. However after a few minutes of driving the cabin goes stone cold and the car overheats again.

 

There's no symptoms whatsoever that point towards the head gasket, and Ive been driving it this week for a good few miles with no troubles, bubbles or signs of oil in the water.

 

I hope this all makes sense!

 

If anyone has any ideas at all please let me know and both Chris and Bob are verging on chinning me because we cant work out what it is.

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Bring the car to me & Octet @ the real zed shed & we will fix it for you

 

Your on - I'm lost at the moment - all the signs point at it being thermostat as when we take it out the car runs fine no overheating etc - when you put it in the lower hose is cold - so no circulation and the car overheats - had we not tested and used 2 thermostats I'd say it was that.

 

So how long you need it for? just the day???

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Im not sure about the sensor mate however id guess its pretty bang on as when its overheating you can hear the water boiling and steaming out the top of the expansion tank.

 

as for the pump wouldn't that cause less pressure to build anyway, thus keeping the thermostat open allowing the water to flow? it really seems like once under load the thermostat decides to close as like Chris mentioned the lower pipe into the radiator goes stone cold

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Water pump? Temp sensor? is the ecu reading water temp? whats the gauge showing?

 

Are the fans working?

 

Well when it's not overheating the gauge shows normal

 

When it is over heating and has steam coming out the expansion tank the gauge shows HOT

 

Water Pump - works fine when the thermostat is removed so unlikely but we did consider it.

 

Fans work perfectly

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Are the fans spinning at all? Maybe they're slow before they're dying, a well know problem on the 350z, causing overheating.

 

Fans are spinning a treat matey....my knuckle can vouch for that :stretcher:

 

Hmm, mine were doing the same thing, they looked like they were working, not seized, but they were slower that they should have been, you couldn't tell the difference just by looking at them. The minute I've changed them with brand new ones overheating was history :)

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The fact that the cabin goes cold is weird as usually it heats up when theres an airlock when moving and goes cold when not moving.

 

I still think theres an air lock though. Id drain fully and fill as stated with the manufacturers instructions which means you will be there for ages doing it.

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Good point Mace

 

Do the pipes pressurise as the temp goes up. If the system doesn't hold pressure 1.1bar I think the standard cap is, then this will affect the efficiency of the cooling system.

 

 

But if the pump & thermo stat are good & all the hoses reconnected (in the right places) I'd be looking at an airlock. The 350z can be a right bugger to fill without getting an airlock.

Edited by Darren-B
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If i had that problem I would be thinking the water pump as it will pump water through the larger radiator hoses with the thermostat removed but put the thermostat back it can't pump water through the smaller hose to the heater matrix may be the impeller is loose on the shaft.

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My guess too Dazza that's as it looks like everything is kosher its an airlock.

It can be painful to get rid but I've devised a few techniques and get it right 1st time now.

 

Fill up slowly with coolant with the posterior bleed nipple open.

When it appears full keep squeezing the pipes sequentially to get some more air out and keep topping up until rad full and replace cap.

Final trick is to raise the rear of the car to make he posterior nipple the highest point on the system.

Fill now will funnel slowly through the nipple while still squeezing pipes intermittently until full. Close nipple

Now start the car and up to temp and put on heating to circulate coolant and more air. While this is happening intermittently bleed the nipple until no more air.

Level out the car and open rad to too up if necessary.

Go for a good spin and repeat the process. Should be job done.

I replace coolant yearly and also use the 2.3bar car to pressurize the system more.

 

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Air rises to the highest point which is the posterior bleed nipple. By jacking the rear you are accentuating this but also helping the air trapped within the engine block to escape towards the top most part rather than go below before rising to the top and burp out through the rad👀

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I don't think jacking the back up is going to make much difference, when y0u fill the system you are always going to get a some air in the system, so long as you have the heater set to hot & fill the system slowly you should eliminate most of it. The rest of it should find it's own way out through the expansion tank. As the temp rises the air in the system will rise in pressure & ill be released into the expansion tank & when the system cools water/coolant will be sucked back in

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