Fluctuating Temp Guage

[Dimes4Life]

I recently replaced my radiator to a (Champion)aluminum and thermostat(180°). I also have a catch can attatched to the overflow valve. I used a kit with a non spill funnel to burp system. Ieven jacked up car & ran for 20 min at idle.I have a auto meter temp guage(15 yrs old)
Upon testing,my temp warmed up to 190°, then on freeway it shot up to 210°.As soon as it hit 210,it bounced back to 190. Did this 3 more times while I returned home.Don't know if I burped right because i never saw it bubble the first time..and fluid never dropped level. I'm wondering why it never bubbled? Figured it was already purged.
The car reaches temp so I'm sure new thermostat is opening. Or is it? Thanx

[510rob]

does the new thermostat have a small bypass hole in it? did you install the thermostat the correct way around?

I assume that a "Champion" radiator has an increased liquid capacity and an increased cooling capacity, but if the system gets up to 190° or 210°, then it seems almost like there is a problem with the thermostat.

(just because something is new doesn't mean it necessarily works. Newness only means that no one has tested that object yet!)

What happens to the water temp if you block off about 1/2 of the radiator area with a piece of cardboard? Does that reduce the thermal spiking, or increase it?

[okayfine]

What kind/brand of thermostat? I've had bad stats out of the box. Ended up going with either the factory piece from Nissan or a Stant "Premium" or whatever they're calling it now. Just any ol' thermostat won't due. I've also had bad stats that failed but still opened and closed...but not properly, so the temp shot up enough to toast a head.

Did you have the heater core open during filling? If so, it wouldn't seem like you have air in the system. What's your fan setup like?

[510rob]

Along Julian's line, throw your new thermostat into a pot of boiling water and get a known (relatively) accurate thermometer, set the water to boil and watch what temperature the thermostat starts to crack open at...

[Dimes4Life]

I ended up pulling new radiator for testing,replaced water pump and replaced thermostat as well...put on burping kit...and away it bubbled...drives at constant 180° now.

[510rob]

I have never heard of a burping kit until now. I just looked it up.

Son of a gun, I learned something new today! Thanks!

[datzenmike]

Your bypass hose is missing. Water around the thermostat is stagnant and not moving. Heat from the hottest part of the engine has to travel there by convection not by flow. The bypass hose flows hot water past the thermostat so it is constantly sampling it without delay. Without the bypass the thermostat is always slow to respond to the actual engine temp. A jiggle valve style thermostat or drilling a 1/8" hole in it will work also.

Can't for the life of me see how it's possible for any air to be trapped in an L series head. The head (and thermostat) is the highest part of the cooling system. Any bubbles will be pushed or rise there. The first time the thermostat opens air flows out to the the upper rad tank. If you have a jiggle valve thermostat air passes out as you fill the cooling system.