Thermostat problem or not.......

[richard1]

The question is how to detect a failing thermostat.

My 72 Z has all the goodies for hot climate (100-118F) including three rows radiator, fan shroud. good fan clutch and 160 thermostat. Also my vapor lock is fixed with the addition of an electric fuel pump.(car is full stock)

My engine runs cool with the A/C on in traffic or highway but since a week I am wondering if my thermostat is showing some sign of weakness. My temperature gauge is normally always below the middle mark. Now it tends to go a bit over the middle mark and comes back to the middle in traffic with all accessories on in day time.

I am a little bit picky here wanting to have a 32 years old car performing like the new kid on the block but until now it always performs flawlessly.

Could it be a sign that the thermostat need to be changed?

thanks for your comments.

[Zedrally]

Why not swap it over with a new one if your concerned about it?

It would be one of the cheaper parts and possibly the easiest to swap in any case!

[richard1]

Your comment is sincerely appreciated.

Other comments from fellow members who have gone through the same problem will be welcomed to go further in this matter.

[MikeW]

I would think you could even temporarily remove the thermostat and see how hot it gets. The thermostat should be completely open at 160 degrees, which, in Las Vegas in the summer is about 2 minutes after starting the car. After that the thermostat serves no real purpose. If at that point you're still running hot then you know it's not the thermostat ...

[sblake01]

I would think you could even temporarily remove the thermostat and see how hot it gets. The thermostat should be completely open at 160 degrees, which, in Las Vegas in the summer is about 2 minutes after starting the car. After that the thermostat serves no real purpose. If at that point you're still running hot then you know it's not the thermostat ...

Not completely true. A thermostat also controls the flow of coolant by restricting the flow to the size of of it's opening. Without it, the coolant actually flows to fast to properly cool the engine and can cause water pump cavitation. You DO need to have a thermostat.

[MikeW]

Without it, the coolant actually flows to fast to properly cool the engine and can cause water pump cavitation.

Interesting; I didn't know that.

[First Gen Z]

Could also be slightly restricted radiator. You didn't say how old the three core was.

[zguitar71]

The 160 thermostat can cause problems by staying open continously. The coolant in the radiator is passing through but not staying long enough to be cooled down. The coolant needs to sit a while in the radiator to cool down then when the thermostat opens a rush of cooler coolant comes into the motor and you can see the temp guage go down. If the coolant does not stop in the radiator but passes through eventually the coolant will build up heat and the motor will over heat (in stop and go traffic not constant cruising). I run a 190 Thermostat and have no problems; I do live in Montana, hardly a hot climate, but we just had a few days recently where our temps were up to 102 and the temp guage did not run any hotter than today at 65 degrees (the guage needle stay in the middle of the "M" on the guage). And according to the book "How to Hotrod and Race Your Datsun" the L24-28 motors run best and give the best performance with a thermostat of 190-195 degrees. I think you might have better luck with a 190 thermostat.

[BuDavid]

I guess that Zedrally is right, change it man, coz it might be jammed! maybe thats why it goes higer that it should and the comeback to normal, it gets to higher degrees than the degree where it should allow flow of fluid where u notice the higher temp. and it allows it and comes back to normal temp..

i guess f u had a radiator prob. or any other prob, u would have a permanent temp rise!

the ifo u got from the gues was really usefull, dont remove the themostat, the engine wont run good, i rather turn off the AC or use my mothers cra than taking out the thermostat and letting the flow free:)

i baught the car without the thermostat, the performance was bad..

good luck with the new one;)

[sblake01]

The 160 thermostat can cause problems by staying open continously. The coolant in the radiator is passing through but not staying long enough to be cooled down. The coolant needs to sit a while in the radiator to cool down then when the thermostat opens a rush of cooler coolant comes into the motor and you can see the temp guage go down. If the coolant does not stop in the radiator but passes through eventually the coolant will build up heat and the motor will over heat (in stop and go traffic not constant cruising). I run a 190 Thermostat and have no problems; I do live in Montana, hardly a hot climate, but we just had a few days recently where our temps were up to 102 and the temp guage did not run any hotter than today at 65 degrees (the guage needle stay in the middle of the "M" on the guage). And according to the book "How to Hotrod and Race Your Datsun" the L24-28 motors run best and give the best performance with a thermostat of 190-195 degrees. I think you might have better luck with a 190 thermostat.

Well, I don't really buy all of that because in your scenario, you're assuming that the thermostat is opening, closing, opening, etc. Engines don't run much below 175-185 degrees so once it's warmed up, especially in a warmer climate, it pretty much stays open. A 190-195 degree thermostat would be considered a cold climate thermostat especially in a 70s vintage vehicle which weren't designed to run as hot as today's vehicles.

[zguitar71]

Well, I don't really buy all of that because in your scenario, you're assuming that the thermostat is opening, closing, opening, etc. Engines don't run much below 175-185 degrees so once it's warmed up, especially in a warmer climate, it pretty much stays open. A 190-195 degree thermostat would be considered a cold climate thermostat especially in a 70s vintage vehicle which weren't designed to run as hot as today's vehicles.

Did you read the first sentence of my post? I am assuming the 160 thermostat is open all the time. I do not think you have a full understanding of the post. The thermostat staying open is a problem. In a hot climate with a constant open thermostat there is more chance of over heating than with a warmer thermostat that opens and closes especially in stop and go traffic. To understand why go back and read my post you quoted.

"If the engine is assembled correctly, it should run as well hot or cold, with less wear if it is warm." That is a quote from the book "How to Hotrod and Race Your Datsun." The info from that book is compiled from the author's, Bob Waar, racing experience and information gathered from the BRE racing team mechanics and from the Electromotive Company. I trust what these people know about the L24-28 motor. I did not just make up the info I gave. The info came from literature I have read.

Many New cars run hotter than 190-195. If the colling system is in proper order the 190 thermostat should be just fine in a hot climate.

[sblake01]

I have done my own testing. When I said 'engines don't run much below 175-185' I was referring to L series engines. I don't run 160 degree thermostats. I run 180s. But in my post (#5) you'll note what I said about it (or any thermostat) controlling the water flow. Warn is relative. 175-185 degrees is warm enough to diminish whatever problems that arise from low engine temperature. If you were not running a thermostat at all, then I could see a heat build up problem in the cooling system cause by too free a flow. Electramotive and team BRE built race cars. I'm basing what I say on experience I've had with street cars. I've gotten a lot of mileage out of my L motors over the years and have never had a cooling system related engine failure. I'm not knocking what you say, I'm just leaning on my own experience.