2007 DF 50 gradient overheat problem

[Tides2]

Hi. - so motor starts and runs fine at idle. Run it at 2500 rpm for a few mins and I get the buzzer every 6 seconds and 3000rpm limiter. Hooked up the diagnostic software and get the overheat grad warning showing up. There are zero overheats and no other errors. Changed impeller and thermostat opens about 60degC - both temp senders appear to have same ohms and increase linear when heated. Took both sensors out ( still connected ) and taped together. Used IR gun to measure temp at sender location - I get similar temp with IR gun and the data log, but when buzzer starts and and I get a caution error and a data log I notice that the exh temp data log reads about 212F and the sender is not near its location . However the IR gun also reads 212F at sender location. It seems I can only read the exh temp when an error occurs and I get a data log

Hope all this makes sense. - some input would be great , particularly the normal temps at the sender points.

[redlowrey]

For the caution system to come on the temp signal wire on pin 9 and the exh temp pin 11 must drop down to around .2 of a volt, with both connected and out side the engine the signal voltage would still be over two volts, so it should not have been able to activate it. 212 deg is too hot, what is the voltage on the inlet air temp on pin 31. Did you check the voltages at pin 9 and 11 because something is not adding up.

[Tides2]

Hi - thanks for informative reply - I've still to measure the voltages but if the exhaust temp readout ( both with IR gun and data readout ) are about the same at 210 to 220F and you say that's too high then would that in itself give the temp grad warning. - what temp should I expect?

data log shows intake air temp at 86F, mean outside temp was about 65F -constant rpm at 2850, cylinder temp 138F and exh temp 209F ( both senders taped together suspended about 3" from outside engine) IR gun read outs were approx 155F and 220F respectively at the sender locations

It almost appears that the ecu retains the exhaust temp readout when sender was in engine

[redlowrey]

Reading data with the sensors out of the engine is pointless, stick them back in the engine get a couple of thin needles so you can slide them beside the pins in the ecu. Start the engine up cold and you will see around 2.6 volts on the pins, as the engine warms you will see the voltage dropping in both pins, flash your temp gun on the head and exhaust and you will see as they get hotter the voltage will get lower. If you see the voltage drop to about .2 to .1 0f a volt the check engine light will flash and the buzzer will buzz, point your gun on the head and the exhaust and if it is around 200f your wiring and sensors are alright and you have a problem.

[Tides2]

Ok - so I appear to have the answer. There have been several threads on gradient overheat but few answers - hopefully I may provide some useful guides to do the process of elimination. With hindsite the most obvious was that the ecu was telling me of a overheat situation with a gradient warning but not enough to show up as an overheat on the data log. The first clue was reading the temp with an IR gun at the 2 sensor locations. The exhaust sensor was reading about 100C at idle and about 115C at a constant 2500rpm whereas the cylinder temp was reading about 50C and 60C respectively- a notable difference. The ECU reads an overheat at 121C but more importantly the temp sampling it does every 10 secs has a parameter variation of 14C up to 95C but thereafter reduces the variation sampling down to little more than 1C - making it very sensitive to triggering a gradient warning. I removed the thermostat housing and the anodes to reveal some of the water jackets - I then copiously sprayed "lime away" into the openings and left for an hour - in the mean time I used a household electric copper wire to poke and pry into the jackets - paying particular notice to the jacket from the thermostat housing down to where the exhaust sensor was and from the first anode poking up the way to where the exh sensor was. There was crud but seemingly not excessive. I then replaced the thermostat housing and connected mains water supply. Full mains pressure sent a lot of fizzing out of the anode holes. I repeated the whole thing again and then reconnected everything back together again. Started engine and warmed up at idle. - temp readout was now about 45C at both sensors. At 2500 rpm the temp was about 50C at cyl and 65C at exhaust. Bingo - a big drop in exhaust sender temp. Result gave me an hour run on the lake with no problems - did not miss a beat - Thanks redlowrey for first suggesting exhaust temp was too high