Why doesn't anybody ever put the probe in the block? Using the drain plug that is on the drivers side? Wouldn't this actually be the best area since its in the actual block??

 

Readings wouldn't be all that accurate since the coolant is only about halfway through the engine. And you still wouldn't have any meaningful reading until the t-stat opened. Plus, as I recall that opening is pretty shallow, too shallow for most temp sensors. You might be able to rig up some fittings, but then it's more trouble than it's worth given the options. My .02.

 

What about where the stock water temp gauge sender is?

 

+1 esp since the stock gauge sux. Only downside is it's a BPST thread so you either need a sensor that will fit or get an adaptor which may place the sensor outside of the coolant flow, or you could tap it (but would advise against that on an assembled engine)

 

Defi gauges are BPST and plug straight in. For example, my oil pressure gauge is plugged into the stock sender location for pre-99 cars as 99-specs don't use it as the gauge cluster has an illegible factory boost gauge fitted there instead. Screwed straight in and no leaks.

 

Think I'd just linearize the stock temp gauge before leaving it completely dead, and keep the low level alarm and light.

 

Don't think it has yet been mentioned, but with a an ECU such as Adaptronic you could just configure the ECU to cut power if oil pressure drops too low, or temp gets to high.

Currently I am doing that with Fuel Pressure.

 

would unplugging the temp sender in the block kill the low coolant function? I thought they were completely separate.

 

I've got my Oil Temp sensor on the Thermostat Block right after it's Exit from the Engine on its way to my first Oil cooler.

My Oil pressure sensor comes from the Oil Filter Pedestal

Water is OEM location on the filler neck

And Boost pressure/Fuel Pressure are coming off a Block that is directly fed by an AN-6 Line from the UIM OEM location.

 

Not sure, but you're probably right and they are separate. It's just that despite the stock temp needle being worse than worthless it would bug my occasional OCD to have a dead gauge on the dash. I know, I know.

 

It''s dead already

 

just thought I'd post my water temp results comparing a temp sensor in the LOWER radiator hose and a temp sensor in the popular throttle body line. A little history; previous owner had installed temp sensor in the lower rad hose and my concern was that the temp coming OUT of the radiator would be too low. I bought a new gauge and installed the sensor in the throttle body line. I left the other gauge installed for comparison. The TB sensor started to read temps immediately. The LRH (lower radiator hose sensor) took about 5 minutes. Once up to normal operating temps (over 180 degrees) the TB sensor was consistently 5-7 degrees COLDER than the LRH sensor. I was shocked. I drove 30 miles. The LRH sensor read higher the entire time UNTIL the fans activated. The LRH sensor is much more responsive as far as changes in temperature. The sensitivity to when the fans came on was obvious to me as the temps dropped 10 degrees and the TB sensor would only drop maybe 5 degrees.

Also, when getting on the boost, the LRH sensor was much quicker to rise (this stumped me since that sensor is no closer to the turbo heat than the TB sensor).

I do believe the TB line is a more accurate reading of what is going on in the motor, but its clearly not a "hot" reading. Most observers think the Lower Rad Hose is the coldest reading. It is not.

Hopefully this helps someone.

Point of all this. As Sgt Blue pointed out to me...... use your readings in a relative sense. Know your cars 'normal' operating temps according to your own gauge and watch to make sure nothing unsual is happening.

 

Did you compare the 2 sensors in a bowl of hot water? Maybe they give different readings?

What temperature was shown on the two gauges when the fans started?

That said, I also have my sensor in the throttle body line and think of moving it (Since the engine is out of the car at the moment). I heard vom RX-8 drivers that they kill this line because it prevents approximately 10% of the hot water going through the rad. I was told they have big cooling issues when driving hard.

 

I seriously doubt your readings are representative or accurate. Look again at MAZDA's own cooling system diagram. IMO one or both of your gauges and sensors is off.
Many FD owners deleted the TB coolant line but not for those reasons. Looking again at that cooling system diagram. It doesn't restrict any coolant from going through the radiator.

 

[QUOTE=Namxi;12123997]Did you compare the 2 sensors in a bowl of hot water? Maybe they give different readings?

I did not compare the 2 sensors in a bowl of hot water. I probably should have but I believed the original Autometer that is in the Lower Rad hose was operating correctly. I could be wrong. The brand new Speed Hut gauge I just installed in the TB line I assume is operating correctly.

For my own purposes I will just manage based on the hottest reading I see. Also, I still have the stock gauge so a glance at that if the other two gauges look suspicious will hopefully tell me more than I need to know. Feel a bit silly with THREE temp gauges.

 

This chart explains why my TB sensor readings were always lower than my upper radiator hose readings. Like you said, the coolant is only 1/2 way thru the engine, and has not reached its highest temperature yet.

 

^Maybe, we've had this discussion before. But my post was in response to why someone would not want to install the sensor in the block's drain plug. And it wouldn't explain why readings from the TB coolant line, which is immediately after coolant has gone thru the ENTIRE block, would be lower than the lower radiator hose.

 

Jim, I agree with you on this. It does not make sense for the lower rad hose to be hotter than the tb line. But when I tested the temp sensor in the lower rad hose a month or so ago, the fans came on at the exact time that the temp gauge read 221 degrees. I believe the ecu activates the fans at 221 if all systems are stock. So I believe that to be accurate. As I mentioned above, the TB line reads 5-7 degrees lower. Usually its right at 5 degrees, but it reacts slower than the LRH sensor so at times it got up to 7 degrees difference momentarily. Turning the fans on manually (through AC) made the LRH gauge drop temps immediately. The TB line dropped very slowly and not nearly as much. I found this all to be odd but I attribute that to the fact that the tb line is not near the fans and the LRH is. I guess one of my gagues could be "off", but the fan test seemed accurate and my brand new Speed hut gauge should be working properly.

 

If your car is sitting at idle, and the fans have not come on yet, there will essentially be no cooling by the radiator. In this situation, the coolant in the lower radiator hose will be as hot as the coolant in the upper radiator hose, and most of the entire cooling system. You cant judge correctly with no fans, or a still car.

Jim,
The diagram shows the throttle body coolant line coming off the back of the engine. Coolant going thru this line has not made it thru the full circulation of the engine. It has only gone 1/2 way thru. If it only goes 1/2 way thru the engine, it cant be as hot as coolant that has gone all the way thru. This fact would account for lower readings from a sensor in the throttle body coolant line.

 

[QUOTE=adam c;12124666]If your car is sitting at idle, and the fans have not come on yet, there will essentially be no cooling by the radiator. In this situation, the coolant in the lower radiator hose will be as hot as the coolant in the upper radiator hose, and most of the entire cooling system. You cant judge correctly with no fans, or a still car.

Adam,

I agree. But just for gauge testing purposes at idle and to make sure that the temp sensor is at least accurate, wouldn't this be a reliable way to test just for accuracy?

 

I think one of your gauges or senders is wrong.

 

This is a good point and something I hadn't considered Adam. On the other we'll just agree to disagree...I hope. Our experiences differ.