Megasquirt giving misleading readings....
Posted: Sun Jun 05, 2016 3:25 pm
For a while now, I've been occasionally seeing mad temps on my RV8, up to 118C. Towards the end of last year I spent a fair degree of time faffing around with a Wipy microcontroller and a bunch of DS18B20 temperature sensors. These seemed to agree with my suspicions, but as I had them strapped to the outside of hoses they weren't really giving me the true story. I had originally planned to put a couple of sensors directly in the radiator, but I had shied away from that in case it went wrong and I broke the rad.
It then dawned on me that I had a couple of steel pipes helpfully in the pipework on both sides of the rad, so I JBWelded a couple of sensors in. If it all went wrong I could just replace the pipes or drill out the sensors and weld the holes back up.
Anyway, I put them in, topped up the coolant and went for a drive, knowing that I probably had a chunk of air still in the system. I did about 8 miles, and the CLT reading on the megasquirt did this :-
Temperature goes gently up, thermostat opens and then it oscilates until it rapidly climbs to 118C. I got about 400m and then bottled it and pulled over. As suspected, a lot of air in the system and I used the bike valve to depressurise and topped off with a bottle of coolant. I got home and pullled the log file for the sensors actually in the coolant flow and they showed this :-
Blue is the coolant coming out of the engine, red is the flow back from the rad, temps are in hundreths of a degree, so 8023 is 80.23C. This looks much more like I'd expect (the downward spikes are just a bit of noise in the readings) I've also highlighted on both of them 960 seconds into the log where the MS is seeing 118C where as the top hose temp is a much more reasonable 80.12C.
I've got an Offenhauser 360 manifold, and to get the sensor that came with my MS to fit, I used an adaptor. I think to length of this adapter means that the sensor is not actually in the flow and more prone to bubbles.
The car seems to be running fine when the MS reports mad temps so I'm going to keep an eye on it for a while but I have more faith in the temps I'm measuring directly in the hoses.
Thoughts anyone?
Regards,
David
It then dawned on me that I had a couple of steel pipes helpfully in the pipework on both sides of the rad, so I JBWelded a couple of sensors in. If it all went wrong I could just replace the pipes or drill out the sensors and weld the holes back up.
Anyway, I put them in, topped up the coolant and went for a drive, knowing that I probably had a chunk of air still in the system. I did about 8 miles, and the CLT reading on the megasquirt did this :-
Temperature goes gently up, thermostat opens and then it oscilates until it rapidly climbs to 118C. I got about 400m and then bottled it and pulled over. As suspected, a lot of air in the system and I used the bike valve to depressurise and topped off with a bottle of coolant. I got home and pullled the log file for the sensors actually in the coolant flow and they showed this :-
Blue is the coolant coming out of the engine, red is the flow back from the rad, temps are in hundreths of a degree, so 8023 is 80.23C. This looks much more like I'd expect (the downward spikes are just a bit of noise in the readings) I've also highlighted on both of them 960 seconds into the log where the MS is seeing 118C where as the top hose temp is a much more reasonable 80.12C.
I've got an Offenhauser 360 manifold, and to get the sensor that came with my MS to fit, I used an adaptor. I think to length of this adapter means that the sensor is not actually in the flow and more prone to bubbles.
The car seems to be running fine when the MS reports mad temps so I'm going to keep an eye on it for a while but I have more faith in the temps I'm measuring directly in the hoses.
Thoughts anyone?
Regards,
David