I just picked up another ride, stock ecu this time!

Been tuning it out as it was in a bad need, and I've noticed the coolant temps acting rather funky.

The pulls will start about 184-188, during a 3rd gear pull they may gain some temp to about 192 or so, and after I let off they keep on climbing. I've seen it report as high as 220 one time, generally it will cut out at about 203-212.

Mind you the dash guage(different sensor....) doesn't move at this time, 220 it should be pegged! I'm trying to decipher between a faulty sensor or a true issue.

I also notice that the temperature will fluctuate just driving around, staying roughly 188ish, but pull to a stop and it could go up to 192 or down to 185...I have been able to detect a very small movement in the stock guage at that time.

I'm puzzled, I have not had time to physically check the temp with a radar temp gun. Anyone ever seen anything like this?

 

Sounds like possible air pockets in the system and/or you need a new tstat.

The factory temp gauge doesn't start moving until a logged 230. They call it an idiot light for a reason, it's slow to respond.

 

Awesome, thank you! I don't remember it having to get that high on the AEM before the gauge went up, but I'll take your word for it!

I ordered a new thermostat to try, what is the best way to bleed these systems? Apparently I'm not doing something right.

 

my mechanic did this yesterday for me

raise front of car up 50cm ish...

grab a 500ml coke bottle (or whatever), cut the bottom of it off.

take of radiator cap and yam/stick coke bottle in upside down.

take out overflow pipe of resoivor, and put upside down someplace

start car. let it warm up.

every now and again squeeze the plastic pipe that goes INTO the radiator (at the top)

once the tstat opens there will be lots of bubbles and stuff.

keep squeezing. and rev the car a little (using tps cable)

the level of the coolant will come up into the coke bottle during this whole time...

when the fans kick in the coolant will shrink and suck back into the radiator. fill if necessary

then stick the cap back on and put the overflow/resoivor back in..


DISCLAIMER: I am pretty sure this will be fine - but becareful, heat etc... dont burn yourself, wear glasses and gloves and longsleeve shirts etc...

 

The temp gauge uses the single wire sensor. The ECU uses the 2 wire sensor. Air pockets can cause the fluctuations. I have also seen corrosion on the sensor cause some odd readings.

 

This I was aware of. Wish we had a vacuum system at our work.

The car has almost 80k I'm going to replace the thermo for peace of mind and bleed the system. Thanks for the help!

 

Update: Replaced the thermostat and completely bled the system, problem still exists.

At steady state cruise(interstate..) the temp will fluctuate between 188 and 195. Make a pull and it goes from 188 to 192 during the pull, then after you let off it will climb on up to about 206 I saw last nite.

Funny thing is, after making a pull I realized the dash guage had dropped 50% of its normal position. Instead of being halfway up it was only 1/4. Within 30-50 seconds it is back to normal

 

That sounds more like either an electrical problem, or the temp sensor is actually going bad.

Have you checked for a possible bad connection somewhere?

Take the plug off the coolant temp sensor, probe it with a continuity meter, and wiggle the heck out of the wiring harness to check for intermittent electrical connections.

188 at a steady state cruise sounds a touch high too as at steady state crusing in my car, it holds right at 177-179 ish. I don't think I have ever seen my car log 206 after a heavy pull. Maybe high 190's, but not 200+.

 

You gonna go with Advance Autoparts special or with RalliArt thermostat?

 

I went with a factory Mitsu one, where I work we order from WorldPac and they sell some factory parts.

The electrical issue is what I have been thinking and afraid of. I was just hoping someone would go, "oh yeah, I've seen that problem, its this..".

I'm wondering if the ECT sensor for the ECU is bad, and when the temps climb some it turns the cooling fan on, and by the time I'm done with the pull it has pulled temps down, thereby why the factory gauge is dropping.

I'm gonna go trace the diagram and see what actually triggers the fan, I would guess it has to be the ecu. Wish we could log that via the MUT tables...

EDIT: Pin 21 Radiator Fan Output

 

You sure you don't have a blown headgasket?

 

I would expect the car to be pushing coolant, no?

Its not pushing or using.

 

Compression checks out, not pushing coolant, so I'd like to rule out a blown headgasket, unless there are some other methods of checking?

 

The coolant sensor is a negative coefficient thermistor. As temperature decreases, resistance increases.

As per Mitsus manual

1. Drain the engine coolant. (Refer to GROUP 00,
Maintenance Service − Engine Coolant P.00-44.)
2. Remove the engine coolant temperature gauge unit.
3. Put water temperature gauge unit into the hot water in
specified temperature, and ensure that basic resistance is
within standard value.

Standard value: 70C° (150°F) 104 ± 13.5 ohm

Temperature Resistance Ω
50°C 230 ± 23
60°C 155 ± 15.5
80°C 73 ± 7.3

Place one lead of your ohmmeter on the single male end of the sensor and the other ohmmeter lead on the hexbolt that you used to remove the sensor

 

How many miles on the car?