BillardCrow

1999 XJ Sport


Noticed the other day that the engine temperature was running slightly lower than the normal ~210.

Change out thermostat for a new Stant 195 (drilled bleed hole) and now the temperature is running even cooler than before?


Any thoughts on what to look at next?

salinity

I recently installed an in-line digital coolant temp sensor in my 95 so for the first time in 10 years of ownership I'm seeing what the temperature reads as I drive - and it's quite variable. Typical driving around town in 50-55* weather results in temperatures between 185* and 202*. I assume the variation is due to the thermostat engaging (195*), as well as the amount of air moving through the radiator. But I'm not seeing 210*.

I'm assuming it's cool in Indiana nowadays, so it could be an artifact of cooler ambient temperature coupled with a more efficient cooling system (new t-stat). I'm also not sure what the lines represent as far as actual temperature readings on that particular gauge.

djb383

Any motor will run cooler in cooler weather. Drilling a bleed hole does nothing but slow down engine warm-up AND in cold weather the bleed hole can lower the operating temp to below the t-stat rating number. There is a dime sized hole directly beside the stat that will bleed air. Did u look closely at the new stat?.....it probably had a small "V" notch in it that is a "air/coolant bleed".

bigbadon

How big of a hole did you drill?? Don't really need it for most thermostats but if you drill one it should be no larger than 1/16" at the HIGH 12:00 o'clock position.

SomeGuy138

Looks like typical running temp to me in cold weather,That's about where mine runs when it's below 20f outside.

Mountaindog

thats what mine runs at , seems normal

BillardCrow

right around 1/16"...but maybe it didn't need it.

Thing is the temperature (per the gauge) has always for 8 years ran at ~210. It all of a sudden started running lower (before I swapped stats). Then after the stat swap it ran even lower than prior...according to the gauge. Not saying it is or isn't normal...but it is definitely a change from where it has been for 8 years so it leads me to think there is something causing it to be different????

Roler

The hole on your stat is fine, the OEM came with it, dont worry about it. Dont worry too much about your lower than normal temp either, the gauge reading you could verify with temp gun (or OBD2 scanner with live data, which is what I did and although it showed the gauge being a noth under 100C (midline, whoch would be your 210), the scanner reading live data showed 94C). So, your reading, if true, is still within normal operating temps.
I doubt that the hole with have any significant influence on warm-up temps, but djb and myself have been known tosometimes have different views on cooling system components
But cooler weather, somewhat cooler temps, not abnormal.

djb383

The problem with a drilled hole is that it slows down engine warm-up as it constantly "bleeds".....the OEM jiggle valve stat does not "bleed" when the motor is running so warm-up is quicker.

Roler

I think we're turning cents here.
On a total capacity of over 11 liters of coolant, the ' bleeding' from the hole which at some point will occur, is negligible. Air bleeding prior to that is more the purpose of it.
Thermostat will start to open not long after, which will be letting significantly more coolant pass then that little hole. I think the OP should just not be concerned about all this, thats all.

steelybill

Maybe the new thermostat opens at a bit lower temp than the specified 195 degrees. Nothing is always perfect...

bigbadon

Flow rate through a 1/16" orifice at 10 psi delta/p is .00268 litres per second. At that rate it would take over an hour (68 minutes) to circulate 11 litres!

djb383

The point is, with the "bleed" hole drilled in the stat (which is unnecessary), some coolant flows thru the radiator, cooling a cold motor even though the stat is closed, thus slowing motor warm-up compared to when there is no flow thru the rad. The OEM stat "bleed" hole is fully closed when the motor is cold thus making for quicker motor warm-up. The OEM "bleed" hole opens only when the motor is off.

Roler

Thanks for doing the maths, BB. Kinda says is, doesn't it.
djb, that calculated amount seeping through the hole, causing "flow" through the radiator....to delay engine warm-up....sorry...I'm probably missing something here, but really, I think I'll move on...

djb383

The motor takes longer to warm-up when coolant is flowing thru the rad than when coolant is not flowing thru the rad.........it's that simple, really. I'm sure there is a mathematical formula that will verify that as well.