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Overheating issues?


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Before I tore my car down a while back I had been having some overheating issues. I replaced the radiator and cap, thermostat, and purchased an electric fan from MSA. While my engine was out I replaced the water pump and freeze plugs (noting a LOT of crud in the coolant passages between cylinder jackets). I just got the Z back on the road this week and last night while I was driving through traffic my temp guage kept creeping up to the red several times at stoplights. Today I was determined to figure out what was wrong. I thought it was either the clogged coolant passages or my carbs are too lean (haven't tuned the ones on the car yet because they were on it before and worked fine, and I'm going to swap on polished ones for tuning). My coworker gave my a coolant system pressure checker and everything looks good on that end. I turned the idle adj screw (on the bottom of the carbs) out just an 8th of a turn and took the car out for a spin. It seems to have worked I guess because the guage only went up 3/4 of the way, but that still seems hotter than before I had all this trouble.

So what to do now? Should I still flush the coolant system for good measure? And also, the trigger for the electric fan from MSA only turns on at about 3/4 up the guage. Should I get a different trigger than activates the fan sooner? (I was thinking a switch from hotronics http://www.hotronicsproducts.com/cooling.htm)

Thanks for any replies. I realize I'm bringing up a topic that has been beaten to death before, but none of the usual solutions seem to be working.

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First thing you should do is validate your temps, with either a mechanical temp gauge or a good thermometer in the radiator. The stock gauges are notoriously innacurate. If the temp is higher than it should be, then you really ought to do a good flush.

Secondly, is this one of those temp sensors that clamp on the outside of the hose? If it is, I wouldn't trust it. I had an electric fan on my race car, and wired it to a toggle switch, just to be sure it came on when it was supposed to or whenever I wanted it to.

Always best to make sure you really have a problem before you spend money and throw parts at the car. You never know, you might not have as bad a problem as you think.:ermm:

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Yes, this gets beat to death, and to what end? It seems I read several posts a month between Z-home and 240.org concerning this topic. The solution is quite simple.

A well-running, properly tuned, clean, happy, well-lubricated, free-breathing L motor with an adequate cooling system DOES NOT OVERHEAT. Period. Yes, that means even in traffic.

Go make your motor happy. Your cooling problems will disappear.


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All good advise, particularly making sure your temp readings are valid.

I had a similar problem in a different car (actually a Dodge Caravan). No leaks, good water pump, flushed system, etc., but gradually, over a period of time running hotter and hotter.

Turns out the rad was clogging up, even though coolant easily ran through it from rad cap down out the lower rad hose. So the coolant was flowing freely, just not getting cooled on its trip through the rad. Changing the rad solved the problem (re-flushing it didn't help).



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I just reread your post and see that you have replaced the thermostat , is it a after market one or factory? Another thing did you test it before you installed it to varify that it worked and at the correct temp ? Always a good practice. In my experience the factory part has a larger whole for the fluid to pass when the unit opens , thats why I asked . Recently there was a post on this vary thing with pictures . Any by all means check the temp with a candy thermometer to varify the gague, as 2manyZs suggested, I would do that first. my 2 c.

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Ok so I put in some cleaner that needs about 3-6 hours run through time. I decided to check the temp manually and I guess my guage is wrong (it reads 3/4 at 180degrees). I didn't think it would be the guage since most everything else is this car has treated me so well. I should have checked that sooner though. So should I replace the sending unit or the guage first?

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While cleaning up my engine, I replaced the thermo housing with one from my former 72, that I had polished. After ward, My gauge read 15 degrees higher. Since the only thing I changed was the houseing and sensor, and kept the same thermostat, I suspected the sensor output was different.

So, I polished up the original and swapped them out again and the gauge reads normally again.

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If you're getting a reading on your gauge, then I wouldn't suspect the sending unit. It's obviously working. I would suspect the gauge, though.

The gauge works of a bi-metallic strip for moving the needle on the gauge. Not a perfect (or accurate) science, but enough for a general reading. There has been an article (about 2 issues ago) in Sport Z Magazine about this very topic. You have two options:

1- Take resistor set up that will read the temperature you want to see on the gauge. 32 Ohms is what you need to read 193* F. Then check to see where the needle lands at this temp. and keep that in your mind as you drive the car from then on.


2- Take your gauge apart and "adjust" it so that it reads the temperature to scale (or to your satisfaction). This 2nd option is more difficult. And I'm not inclined (or able) to discuss it at this point.

If you dediced to replace the gauge, you will still run into the same type of situation as the new gauge is made the same way and has the same type of characteristics. Take your pick...

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