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Discussion Starter · #1 ·
Hi -

TEMPERATURE ANXIETY !

I notice that as I drive my 1973 240Z around the temperature guage
wanders a little bit, from exactally in the middle, to maybe 3/4 the way
up the guage (needle over the "M" in temp).

Details: I put in a nice dual Flex-A-Lite electric fan with the variable temperature sensor gizmo with the thremocoule that sits in the top radiator hose. It seems to come on OK - I actually wired in a little light
that comes on when the fan does. It mostly comes on in traffic, or
if I really punch the car when driving up the highway - just for a 20 seconds or so at a clip.

Anyway, even when I had a mechanical fan I noticed the upwards drift
in the guage. Is this normal? I replaced the sensor a while back. Heck,
I replaced the old 240 engine with a 280 engine while I was at it. Lots of
changes.

ALSO: I had an overheating scare awhile back. I sprung a leak at the valve under the passenger side dashbord and lost a lot of coolant. On the maiden voyage after the engine swap. I don't think I warped the head - no oil in the water / water in the oil or anything. Compression is 180+ in each cylinder.

As you can tell - I have TEMPERATURE ANXIETY !

Stephen in New Jersey
 

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I had some similar experiences that lasted for almost a year. In that time I changed the rad, the cap, the thermostat, the clutch fan...everything but the waterpump. I also noticed that I was very gradually losing coolant. That's when I realised that it had to be a very slight headgasket blow situation. I know that "headgasket blow" and "slight" shouldn't occur in the same sentence, but I drove like that for a year, so I'd say it was very slight. It did not show up on a compression test and my plugs don't look steam cleaned, though 2 did look cleaner than the other 4.

Anyway, not having the money to get the HG changed, I was given the advice of a very good datsun specialist mechanic and dumped in some sealer pellets into my cooling system. It's fixed. I don't feel fantastic about dumping the stuff in, but it's better than it was and any improvement is better than leaving it the way it was.

I guess what happens is the water level in the block goes down and doesn't get replaced until it gets hot enough to open the thermostat. Without the thermostat being immersed in water (it's at the top - above the coolant level). Eventually the block gets hot enough (high temp reading and rising) that the steam heats the thermostat enough to pop it open. Then it very suddenly (as mine did) cools and cools fine after that. Then, the next day I'd hop in the car and it would do it all over again. I'm glad I figured out what it was. Now all I need is a bunch of money to get it fixed. For now - it drives super great - very cool and steady.
 

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Discussion Starter · #3 ·
Hi -

I don't think I'm loosing any coolant, so maybe that is not my particular problem. How high / hot did your engine get when it had the "slight leak"
before things righted themselves? Maybe the problem would have been also solved if you had removed the thermostat and replaced it with a restrictor plate?

SW
 

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All I can say is that I replaced a bunch of stuff when my car did roughly what yours is doing and it was something else entirely. I really didn't notice coolant disappearing and I did all of the things you do to check for a blown gasket. It was consuming (maybe) 2 litres a month and not very noticable, but it was just enough to create an air pocket at the thermostat which interfered with it's function. I'd bleed out the air and it would happen again and again over a period of time.
Perhaps you can bleed any air out of the system and see if it works fine for a very short while. If it comes back and you have to bleed it again, you're getting air in the cooling system from somewhere.
 
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