jeepnuts311 said:
i ran a 160* thermostat for a long time
i got 19mpg hwy consistantly on 35s with 4.88s, about 17 city. i never noticed anything "bad" about the 160* thermostat on my RENIX.
-Tim
Got to remember the cooling is a package. Air flow, outside temp. coolant flow and the amount of BTU's the motor is making.
A couple of other factors is the temp. gauge is on the top rear of the motor and the temp. sensor is on the lower left of the block (Renix), *near* the coolant inlet for the block (water pump) or the outlet for the raditor. Oulet for the radiator is supposidly the coolest spot. 160 means the temp. the thermostat begins to open, there is a window betweent full closed and full open. It doesn't fully open until the temp. gets well above the advertised rating. And is constantly adjusting coolant flow to try and keep a constant temp. while at the same time the engine RPM's are likely constantly changing, causing the water pump to try and increase flow and the motor to produce more BTU's. The whole process has a lot of lag and is far from constant.
The motor switches from open loop (mostly computer controlled) (typically rich for warmup) to closed loop ( mostly sensor controlled) (typically lean for emission reasons) at about 1/4 scale on the temperature gauge (+/- depending on the accuracy of your gage). And the warmer the motor gets, the leaner it runs (mostly, though the computer will likely try the quench with a richer mix if the motor gets too hot). A cooler thermostat will likely take longer to get the motor to operating temp. (and waste fuel) and can also affect the HVAC heater fucntioning.
I spent about 8 hours over two days with my 88 XJ hooked up to an emmisons tester (poor mans dyno). HC, O2, CO and fuel air ratio. My results were pretty much, the higher the temp. the higher the *air* to fuel ratio and the lower the emissions (leaner running/less fuel). I blocked various degrees of the radiator (with cardboard) and tested at various RPM's. Though the O2 readings (available oxygen after the cat and the catalytic process) can get too low, if it gets too hot.
160 thermo and a partially plugged radiator may get the job done, for awhile (though likely isn't a permananet fix). One of the choke points is the radiator inlet (pretty darned small) or a partially plugged radiator. If the 160 deg. thermo runs the motor at around 1/4 on the temperature gauge or lower, you likely have good flow and it's likely winter or nighttime (the end result may be different in the southern states and the northern states and time of year). You are likely burning excess fuel if the system switches from closed loop to open loop and back again very often (if the temperature gauge hoovers at around 1/4 scale plus or minus depending on the accuracy of your temperature gauge). As the thermostat tries to stabilze the temerature with the lag in the cooling system flow (thermostat/RPM) and the temperature changes. Before replacing a bottom hose, I pushed a sharp temp. sensor through the bottom hose, connected it to a fast electronic thermometer. The temperature swings were fairly pronounced, with a (nearly new OEM) stock thermostat. I'm a curious sort of guy.
If you have a switch on your electric fan and a standard mechanical fan, turn the switch on and put your hand in front of the radiator on the mechanical fan side (especially without a shroud). It's likely you will feel air slightly comming out the front through the radiator backwords (no chit). The engine compartment on the XJ flows air poorly. At highway speeds, the air dams in front of the vehicle, flows slower over than under and hopefully under the vehicle has a lower millibar pressure than over the vehicle (XJ does have the aerodynamics of a brick), which hopefully helps the air flow through the engine bay some. I doubt the spoiler they put on the front of the XJ was for aerodynamics, it was likely to help the radiator air flow. Raising the back of the XJ can also help reduce the millibar pressure under the XJ (as it will with most vehicles). The converse is likely true, raising the front will increase the millibar pressure under the vehicle which will likely slow the air flow through the radiator (and engine bay).