Short Stillen Write-up on Dyno + coolant temps

[PalmerWMD]

http://www.stillen.com/news_select.asp?id=60

[Q45tech]

As I have been warning Q owners for years that the coolant temp reading is critical due to the summer ignition advance removal program!

However whether Stillen is right as to a 187F drop vs 195F [my findings that Nissan has always used in the last 15 years?]. Maybe they should have measured and provided the air intake temperature? It would have been nice if they had run/shown the effects at 200F.

Anyway it shows that the radiator must be kept clean inside and out and the thermostat checked for accuracy.Plus an accurate external DIGITAL add on coolant temperature indicator is a must for running and diagnosis.

The ecu coolant temp thermistor is speced to be accurate +- 3F since 195F or 187F is the critical point, it could be trimmed to be absolutely accurate at one specific temperature 190-200F. But you'll need a Consult to see what the ecu interpretes as the temperature.

BUT I would never try to cheat it by modifying it to read low by more than a few degrees as the knock sensor will just make matters worse: trying to gain 1-2 degrees [with coolant temp] and suddenly losing 5 degrees [to knock] doesn't make sense if you cut it too close.

[PoorManQ45]

Plus an accurate external DIGITAL add on coolant temperature indicator is a must for running and diagnosis.

I'm just wondering. Why does it have to be a Digital temp sensor? Why not an Analog temp sensor?

[Q45tech]

Because you need to resolve 1.0F increments as the starting point in the ignition reduction is a coolant temp exceeding 194F [and 5F steps thereafter] of course having uncalibrated sensors and electronics with a +- 3F accuracy is a no no.

Most analog gauges [small sized dials] might let you guess at a +- 5F reading at best.

I recalibrated my ecu/senor to be 1F accurate at 194F from the optimistic [BAD] 198-199F reading.

A 1 degree retard at 6500 rpm translates to about 5HP but you are constantly balancing being on the edge of knock with going over the cliff and losing 25-50 HP...........the inlet air temperature is critical in Summer [above 80F] as the fuel's knock sensitivity is a function of air temperature.

A 10-20F hotter inlet than necessary can undo all the good work of making the coolant temp reading accurate.........because the 1st step in knock retard is -3 degrees ignition advance. DEPENDS ON FUEL.

But you can build circuits to desensitize the knock sensors by 10-20% [safe for most and longevity].

All of this is useless if you don't have a Consult to see and record the ignition advance vs rpm and temperature

[Q45tech]

The following graph shows the resistance of the Nissan coolant temp sensor vs. temperature. If you study it you will see that each 1F is ~~ 3.75 ohms [+-] at around 176-195F but each sensor is slightly different so a 25 ohm variable resistor [NOTHING LARGER] in series with the sensor should allow you to ZERO in on a 6-7 F readjustment range.

What I use is a fixed resistor in series with one lead of sensor with a toggle switch* to short the resistor out for cold weather use........the coolant must get to [read] 176F for the ecu to be happy.

DON't get greedy and blow the engine from fooling ecu too much.

Years ago BMW had a series of switches [in EURO models] which trimmed the ecu to adjust for Summer/Winter fuel/ regular fuel, what these did was vary ignition advance and coolant temp and fuel enrichment: Zero, -2%, -4%, +2% +4%.............6 slide switches tuned the ecu for German or third world fuels and temperatures...............all this went away with OBD1 in 1985.

You must know exactly what the ecu is reading as the coolant sensor temperature!

[Q45tech]

Almost every Q I've tested runs hotter than 195F [as read on Consult showing what ecu sees] in Summer with AC on...........some even read this at highway speeds [with AC off] due to partially blocked air flow or cooling system crud.

The thermostat is wide open at 194F [if brand new] and you are at the mercy of the radiator.

Why owners notice so much power drop off in Summer [more than the 3-5% one would expect from air density changes].

If your 50-80 mph [NO AC] times increase more than 0.2-0.3 seconds in Summer [from 70F ambient] you know you have a coolant system problem.......assuming oem stock intake and test after 10 minutes at highway speed [to stablize coolant].

[Q45tech]

Interesting note from a Jag V8 website:"At high engine loads, the air intake temp sensor retards the timing 2.25 degrees every 10C above 86F (30C), "

Now many Nissan have air temp sensors and radio stated temps of 80F probably exceed 86F at the air temp location.

http://www.jag-lovers.org/mode...12.14

The above explainations seem similar to what you would find in a Nissan ecu.