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260z Overheating issues

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Hello Their,

I'm new to the forum,

 

So I purchased a 1974 260z 2+2 off a fellow member and since I have had it I can't drive more than 15 minutes without it overheating.

so I have tested the thermostat, flushed it, checked fan,checked water pump cleaned it out all new gaskets screws and sealants, clean out rad,

pretty sure not the head gasket.

Noticed oil smelt like it had a small amount of petrol in it, checked hoses were not collapsing, seems to be ok while idling in driveway.

Ordering new aluminum radiator just in case, rich while idling.

would really appreciate some ideas and advice thank you.

Taner

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i would seriously just change your thurmostat, same thing has happened to me twice and both times it was the thurmostat, they appear to work but just dont open all the way what you can do is take it out see if it overheats if not then its your thurmostat.

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+1 to Thermostat.

Assume when you say 'overheating' it's the gauge reading high? Check the radiator/hose and make sure it's actually getting hot (water is flowing past the thermostat). It's such a cheap item and so easy to replace you might as well! :)

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Ok so I ran it without the thermostat still gets really hot, no it actually overheated and pissed out fluid everywhere gauge got to 120 :(

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if you take out the t/stat water has no restriction so it flows so fast through the radiator it cant cool down therefore boils, put in a new one and try it my guess is h/gasket or even w/pump.. when it is idling with the cap off any bubbles coming up??

Linton

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If you do have bubbles and you loose water, it can be  a cracked head, compression super heats the water .

I would try a bottle of Chemiweld before starting to pull things apart, I managed to get 5 years out of Cressida with a bottle each year. It was pouring water out the exhaust, blowing water out the radiator, and oil in the water and water in the oil, running on a couple of cylinders sick as, 5 min's after treatment runs fine.

My Bob cat has now gone 5 years with one bottle.

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Has the car sat around at all with no water in the system at all? That happened in my case and all the sediments dried up and hardened in the radiator and blocked 3/4 of it.. drive for a bit and it's ok then shoots right up to over heating. I'm with Benny, thoroughly check your radiator...

Also check for a temp difference (with your hand before it gets too hot) between the top and bottom rad hose; if the one near the thermostat is cooler than the lower hose, water is not circulating ie could be either rad or tstat.

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Give it back and get a refund.

 

Let us know who the member you purchased it off is and we'll fix him up :)

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Check the ignition timing my volvo 240 was set at 40deg advanced which caused it to get hot enough to blow gaskets. When I ran my Z after replacing the head it also ran hot until I got the timing right.

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Another item to check is the water pump...........the pump veins can rust away to nothing and inhibit circulation.

 

If your radiator is clear, your thermostat is Ok and you water pump good then look for a blown head gasket, easiest way is to pull out the plugs and look for one that is has been steam cleaned.

 

Also make sure you have flushed your cooling system with a radiort flush to get the gunge and rust out of the water jackets around the block.

 

my 2c

 

Al.

 

 

 

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Looks like that might be my old bus that I sold to another guy on here ;) Different engine to when I had it though.

 

Is it a 3 core vl or vn or 'whatever bloody crappy car' it comes off radiator? And does it have a 12 inch thermo fan on it? If so it did cool fine with daily driving on the old engine, even in traffic in summer. I think the thermo fan controller might have been fried when I sold it, I assume they fixed this or might have replaced with an original fan setup?

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Yeah definitely agree with the other boys.

 

Replace that thermostat first      >>  try chemiweld (even a few bottles)    >>      then pull your waterpump and check that

 

I think most likely waterpump but other 2 are easier to try first ;).. also just make sure to keep an eye out for milky looking coolant, sure sign of problems in the head as it leaks oil into the coolant

 

Good luck!

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Radiator Cap too!

I think we missed that one! Dodgy cap will stop the system from pressurising properly so could cause the coolant to prematurely boil. Plus they are cheap and just about the easiest thing to replace on the whole car (provided it's not actually overheating and spitting boiling liquid at the time).

 

Correct me if I'm wrong there, that's just what my limited understanding suggests!

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You would be right Daedalus! That would have been the first thing I tried, after that feel the top and bottom rad hoses when the car is warm to check for blockages.

 

After that I would be looking at the thermostat and then the radiator. In this case start with the cheapest item and finish with the most expensive 8)

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if you take out the t/stat water has no restriction so it flows so fast through the radiator it cant cool down therefore boils,

 

I've read this statement before on this forum, pretty sure it is incorrect. Increasing fluid velocity increases the convective heat transfer, which will improve the efficiency of the whole system, which results in lower average water temperature.

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??? Two other checks for head gasket problems is oil deposit in radiator cap when removed or also a milky colrd residue in oil cap when removed.Compression test is best method to check thoroughly but best take two readings .First one while motor is cold & the second after the motor has been warmed up to allow metal to expand & problem to be more evident. If both readings are fairly close it's not the gasket.If there is a distinct variation of readings then it is either the gasket or the head is cracked.

 

                                                          Regards: Alan.  :D       

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A lot of places have these testers that change colour if it detects combustion gases in the radiator, these gases super heat the water, you can have a cracked head and not show water in the oil or oil in the water,

My 306 pug showed this, and a bottle of cemweld fixed it.

 

images?q=tbn:ANd9GcQmEd2mf_vstosRaQvZVW6PaVYCKfrYptNq8P5-id4K-0j_YCxHa3KO1FcBcA

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I've read this statement before on this forum, pretty sure it is incorrect. Increasing fluid velocity increases the convective heat transfer, which will improve the efficiency of the whole system, which results in lower average water temperature.

 

The statement is correct, which is why companies such as Moroso sell "water restrictors", that get installed in place of thermostats in race only engines.

 

The issue with no restrictor is that the coolant is allowed to flow so quickly, that it doesn't spend enough time in the radiator (and heater core, which is also a forgotten part of the cooling system), that the coolant doesn't spend enough time in the radiator to transfer the heat from the liquid to the metal (brass or aluminum) heat exchanger (radiator). It also works the other way, the coolant can flow so quickly through the engine itself, that the coolant has limited time to "pick up" heat from the engine itself.

 

Another issue is that the coolant can cavitate when allowed to free flow, which reduces the ability for the coolant to actually transfer heat.Air and air bubbles are a very poor conductor, and therefore have a poor ability to be able regulate temperature.

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The issue with no restrictor is that the coolant is allowed to flow so quickly, that it doesn't spend enough time in the radiator (and heater core, which is also a forgotten part of the cooling system), that the coolant doesn't spend enough time in the radiator to transfer the heat from the liquid to the metal (brass or aluminum) heat exchanger (radiator). It also works the other way, the coolant can flow so quickly through the engine itself, that the coolant has limited time to "pick up" heat from the engine itself.

 

That is a common myth. It is a closed system so heat in = heat out. It is not an issue of 'spending time' in the radiator but it is more about the equilibrium temperature reached. Restrictors in race engines are for increasing the vapour pressure as the water flows around the sharp geometry in the block so that it does not boil, as a steam reduces local cooling which can exacerbate already hot spots in the engine. Restrictors do not increase cooling efficiency at all.

 

I found this explanation the best: http://www.stewartcomponents.com/tech_tips/Tech_Tips_3.htm

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That is a common myth. It is a closed system so heat in = heat out. It is not an issue of 'spending time' in the radiator but it is more about the equilibrium temperature reached. Restrictors in race engines are for increasing the vapour pressure as the water flows around the sharp geometry in the block so that it does not boil, as a steam reduces local cooling which can exacerbate already hot spots in the engine. Restrictors do not increase cooling efficiency at all.

 

I found this explanation the best: http://www.stewartcomponents.com/tech_tips/Tech_Tips_3.htm

 

It is not a myth at all.

 

If the coolant does not have sufficient time in a heat exchanger to actually transfer heat from the coolant to the heat exchanger, the cooling efficiancy is reduced. The pressure of the coolant is also a factor, which helps raise the boiling point of any liquid, but time spent in the heat exchanger is very important and wouldn't dismiss the need to control the flow as a part of that equation.

 

You also contradicted yourself, saying:

 

Restrictors in race engines are for increasing the vapour pressure as the water flows around the sharp geometry in the block so that it does not boil, as a steam reduces local cooling which can exacerbate already hot spots in the engine.

 

Then you said:

 

Restrictors do not increase cooling efficiency at all.

 

So which is it, do they help increase pressure to help increase the boiling point (which they as a by product), or don't they?

 

 

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Just playing devil's advocate, but if the fluid has more time to flow through the heat exchanger/radiator it also spends more time flowing through the very hot engine. It all depends on where there is a greater temperature difference as to where the greatest heat transfer aka heating/cooling will occur.

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So "260" have you fixed your o/heating problem , lots of debate here with great tips and you have disappeared, what was out the outcome  :-\

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