So yesterday I decide it's time to change out all my coolant hoses and heater hoses etc. I got the "while I'm at its" so I buy a new thermostat. The one I was going to replace turns out to be a Nissan O.E. brass type 180 degree. My local dealer wants $28.00 for a new one, so I bought a replacement at O'reilly also 180 degree. I install the new one and my car immediately reads hotter on the temp gauge by probably 20 degrees from at least two needle widths left of center line to 1-2 needle widths right of center line. I think, well, maybe I've got an air bubble. I leave the car on my driveway which is a pretty good incline and then jack up the front just to make sure with the car running. confident I have no air in the system, I button it up and take it for a drive. Temp stays solid at about two needle widths above center. Not happy with this result, I bring it home and swap out back to the original and my temp gauge goes back to where it has always been? What the.....

What you don't know is whether either t-stat is opening at the rated temp. Submerge each of them, individually, in a pan of water. Insert a thermometer capable of reading to boiling. Watch the t-stat whilst submerged in the water as it is heated. Note the temp on the thermometer when you see the t-stat open. Do the same with the other t-stat and you'll know which is the more accurate of the two.

If you really want to know for sure what temp each open at, I would suggest putting both in a pan of water with a meat / candy thermometer, slowly raise the heat to observe when & at what temp each one opens.

Frank beat me to it, but I put them both in at the same time.

Bonzi Lon

Edited April 23, 201113 yr by Bonzi Lon

On some thermostat housings, there is a shape to the well under the thermostat where the protrusion has to sit properly.

You can measure the temperature of the thermostat opening in a pot of water on the stove with a thermometer in the pot (thermostat and thermometer suspended in water... not on bottom).

Also the orifice of some after-market thermostats is often smaller than Nissan part.

Did anyone happen mention that you can put the t-stat in water with a thermometer

How unlucky for the responders; three replies at the same time. At least the advice is consistent.

I am a slow typist

btw the thermostats I tested creep open slowly. Watch the margin where the inner metal disk meets the outer disk.

If the old thermostat still works, why not just keep it in? I have a saying, borne by having too many projects to deal with. "If it ain't broke, don't break it."

If you take a close look at these thermostats, side by side, you will probably notice that the orfice opening of the aftermarket thermostate is small than the Nissan OEM thermostat. Another good reason to buy quality Nissan parts.

Dan

I'm with AZ on this one. I don't think it is the temperature in which the thermo is opening, but rather the rate at which the new thermo allows the fluid to go through the system. My bet is the new thermo allows more fluid to go through and it doesn't have as much time to cool while in the radiator.

I'm with AZ on this one. I don't think it is the temperature in which the thermo is opening, but rather the rate at which the new thermo allows the fluid to go through the system. My bet is the new thermo allows more fluid to go through and it doesn't have as much time to cool while in the radiator.

Actually, my point taken is just the opposite. The aftermarket thermostat with the smaller opening, restricts volume of flow and rate of cooling done by the radiator. The Nissan OEM thermostat, with it's larger orfice, allows a larger capacity of flow and cooling. First hand knowledge!

Dan

Agreed. One of my Zs ran much cooler with a Nissan t-stat compared to a brand new aftermarket. I've stuck with Nissan on this part ever since.

In the photograph below, the thermostat on the left is a Stant brand after market unit. The thermostat on the right is the Nissan part for a 240Z. The difference in the size of the opening is significant.