Hello,
Just installed a new water temp gauge on the TB coolant line and have been noticing a 10 degree Fahrenheit difference. Anyone else with similar problems? The sensor on the Defi water temp gauge is brand new.

Jason

 

Not me. The resolution is a little finer on the Commander but in agreement with my Defi gauge, which seems to react a touch quicker.

 

Its been my experience that the TB coolant line sender always reads lower than my pfc. This was particularly apparent on the freeway. It was frequently off by 10 degrees or more at highway speeds.

I wound up installing a greddy 38mm radiator hose adapter. That sender location gives readings more in line with the pfc. The only disadvantage is that it doesn't do much until the thermostat starts to open.

http://www.frsport.com/Greddy-164016...m_p_15546.html

 

Guess the question is, which one is more accurate?

 

I also have a defi gauge, the racer series, it is different than my PFC but not by much maybe 5 degrees.

 

Hmmm, now I'm getting a 4degree c difference.

 

Mine have always been just a few degrees apart at most. If there's a big difference, it's usually air in the throttle body line keeping the sensor from getting a good reading. While burping my cooling system last time the gauge was off by quite a bit until I got all the air out.

Dale

 

How about the fact that you are using two different locations to measure water temp.
Logically you would expect the TB position to be cooler as that is farther away and has allowed the water to cool off some while it goes through hoses and metal pipe.

Some people need to study logic and science some.

 

If I am remembering right, the flow of coolant goes thru one side of the engine, then the TB coolant line, then the other side of the engine. If this is correct, it would account for the difference. The coolant will definitely be hotter after going thru both sides.

 

Farther away from what? A sensor in the t-body coolant line is going to read temperatures from the coolant immediately after it has passed the combustion chambers of both housings/rotors. Arguably one of the hotter areas. It continues on to the exhaust side and may get hotter still...which is what adamc contends. But how does it "cool off" coming from the waterpump? Where's your logic?

 

Does any one know if the coolant passes front to rear thru the TB? If it does, the TB itself can be cooling the coolant before it reaches a TB coolant line sender. This could be one explanation for lower readings while cruising on the highway.

 

From the "Big Fat Cooling System" thread:

 

Always go with safety on temp. Worst thing that can happen to a FD is overheating! I would say whatever one says its hotter is the one you should pay attention to.

 

Agreed. And there is also an issue of calibration....absolute calibrations, production tolerances, the stacking of tolerances, etc., that all comes into play. Here the total discrepancy is about 5%, not all that bad for production stuff and quite normal (even neglecting the sensor location, which is a factor). When greater accuracy is required, you calibrate the gauges to the same standard and under standard conditions.

 

Thanks for posting that Kyle

So, the TB coolant line gets coolant from the back of the engine, which is about 1/2 way thru the cycle of going thru the engine.

As an example, lets say that coolant exits the radiator at 160 degrees. It cycles thru the engine, and exits the engine at 180 degrees. One could deduce that coolant would be about 170 degrees at the 1/2 way point in the engine, which is where the TB coolant line comes out.

In this example, it would seem logical that readings at the TB coolant line could be 10 degrees lower than what a pfc reads.


I honestly dont know what the average temperature drop might be for an aftermarket (which most of us have) FD radiator might be.

 

The heat source.

It may?! If the coolant is cooling the exhaust side of the engine (which it most certainly is) then it HAS to be absorbing heat in the process, thus increasing the temperature of the coolant.

 

Neither? Both? Who knows! Neither have been calibrated to a standard reference.

If you're wondering which temperature it is better to monitor, my personal preference is to look at the highest temperatures leaving the engine, which would be from the PFC in this case.

The engineers at Mazda felt it sufficient to use the coolant temperatures in the rear housing (which are a few degrees cooler than those elsewhere in the system) to drive the temperature gauge in the dash.

 

No, Read his statement...." Logically you would expect the TB position to be cooler as that is farther away and has allowed the water to cool off some"...I ask again, from what? The t-body line is immediately after the combustion side of the engine. That's a heat source, so this makes no sense. It's farther away from the waterpump, but I don't regard the waterpump as a heat source.
Probable, I conceded. But do you have sensor placement figures (with or without a calibrated standard) to confirm? I haven't seen any either. So yes, 'may' .

I simply don't see any significant difference in indicated temperatures between the Commander and the gauge. That's my experience. Besides, as you've noted, it makes little difference...neither have been calibrated to a standard. And each car is slightly different anyway. Additionally most all of us know what is "normal" for our individual cars relative to varying conditions....ambient, driving, load, boost levels, etc etc. And if the indicated temperatures exceed that norm, we'll know it. The specific sensor placement and which location is more accurate won't really matter. Because we'll know it's hotter than normal.

 

I did read his statement. The coolant loses heat making the jump from engine to TB.

Either the exhaust side of the engine is being cooled by the coolant thus increasing the temperature of the coolant, or that side of the engine is cooled by magic.

 

I'm trying to justify your condescending and smartass responses in this thread.

However, I can't. No one else has said anything to warrant the way you are responding...

Maybe if you respond in a much more helpful and understanding manner, people would take your words as advice, rather than just assume you're an *******.

With that being said, the 6 inches or so of coolant hose to the sensor in the TB line will not give a 10 degree drop. I have that portion of the rear iron tapped and my sensor is threaded directly in to the iron. I haven't had a chance to monitor temperatures yet since I haven't completed my build, yet. However, differences in the brand of sensor and gauge could be the only reason you have those differences.

But as it's already been stated in the thread, the "optimum" temperatures are within 10-20 degrees. Either way, I would pay more attention to what gauge reads hotter and make judgement calls on it.

 

Assuming you have a good t-stat, this could be a good way to see how accurate your coolant temp gauge is:

On a cool night, find a long flat road, and drive your car at a steady freeway speed for about 10 miles. No boost!!! Your coolant temp should settle in at around 83c or 182f. It has to be a cool night, and you cant begin the test with a hot engine.