Much like pitpaq below, my 1994 Q45T has an acceleration problem when the engine warms up in hot weather now. Only it is not just when the AC is on. I have read before from Q45tech something about the Timing gets out of whack when the engine bay is too hot.

I am about to take it into T3 for it’s second visit and would like some help with possible causes before I go in. Last visit I did not realize it was only after about 20 minutes of city driving that this started to really affect the performance. Can someone shed some light on what may be going on here?

Thanks and love the forum.

GT

Do a search on the old board...Q45tech was quite specific about how temperatures affect timing. The ECU monitors your coolant temp; the higher it gets, the more the timing is retarded. Possible solutions: use watter wetter in your radiator, keep all shrouding stock, and/or install a temp switch to turn on your condenser fan at a preset temp.

Understand that Redline wetter water helps remove heat from the combustion chamber making the coolant temperature HOTTER as it leaves the head where it passes the ecu coolant temp sensor. So the ecu will see 1,2,3 F hotter temperature, but the radiater is more efficient as the temperature rises so the water returning to the engine will be cooler by 1,2,3,4,5F.Water has almost twice the heat absorbsion capacity as AF so the less percentage of AF you run the more heat it takes to heat the coolant up to a given temperature.Pouring wetter water into a 50/50 coolant doesn't do much vs using it with a 20-25% AF.If your radiator is marginal or your thermostat more than 2-3 years old the coolant system will not stablize at the correct temperature.

Any coolant temp above 190-194F as read by Consult will start a chain of power reduction. The 195-204F range is not too critical as only a 2 degree reduction occurs in timing but this coupled with the 1% for every 11F ambient gets noticable at aroud 90F showing on the outside temp AC indicator as it creates a 5% reduction. But the engine itself accelerates poorly when the advance is below optimum.

If the knock sensors are activated in addition to the above the power drop is signficant with a 10-15 degree advance reduction.

Really the only way to tell for sure is to do a series of WOT runsand record the data, focusing on the ignition advance under load and rpm [ should be 28 degrees at 6,000-6,900 rpm]......have tested some Q which reduced to 15-17 degrees.Good idea to plot the coolant temp vs minutes of idle in gear and learn the rise per minute. Most are 2F per minute so 15 minutes in gear without moving will take you up 30F or more.Which is ok for mine since I might come off an Interstate at 175F so 205F but those with marginal systems in the first place might start at 195F and get to 225F or worse!

Have seen some Q which run around a 220F normally [with a 5 degree timing reduction] then spike to 250-260F [boiling coolant]in traffic and quickly overheat in ONLY 5-7 minutes.

If the radiator has over 70-80k look there first.Getting as new performance [resistance to overheat] always means you end up replacing it.The foam surrounds rot letting engine air suck into and mix with the relatively cooler air in front of the radiator, any restriction in the condenser makes it worse.

There is a new design plastic fan similar to the 94 and up designed to pull a little more at slow speeds.

!!!!!Understand what I relate on this forum is many times VERY technical and not well understood by even T3 technicans and surely not by many/most dealer technicans.They are too use to dealing with customers who don't want to spend to even think of fine tuning.

Intrepreting the 170F thermostat opening vs 194F max lift means an average of 182F and the constant use of the 176F minimum test temp[and the 176F reference for the coolant temp sensor resistance] is an engineers way of implying that 176F-182F is what he designed for!!!!!

My standards are that of the engineers that designed the Q.

I have tested about 9 Q in depth [multiple temp probes, consult, stop watch, 2 hour testing minute by minute logging] and 90% of those with over 7 years needed a new factory radiator and all it's accutremants.

Not many would pay $300 for me to do a diagnostic and provide temp charts, graphs, et all -- when that could just be applied towards replacing the radiator and thermostat.

Is there a way to hookup a multi-meter to the temperature and determine the temp based on either the voltage or resistance? If so, would the best method in determining the temp based on readings be to take a resting cold temp and a resting hot temp and plot the points based on the above. Or would the resulting measurement be based on a curve and not a linear plot.

The manual says that the sensor resistance at 176F is some where between 300-330 ohms. So 4 ohms less per 1F increase would be a good guess but that means the sensor accuracy is [could be off by 5F at 176F].Like all sensors the the graph would be a curve but if you calibrated at enough points.You could by another sensor and an accurate immersable 250F thermometer and get an accurate reading for that sensor at least up to 210F-212F [boiling point of water depending on your altitude].

All the ecu does is supply a very accurate 5 volts to a sensor and the sensor is coupled in a bridge configuration so the voltage varies from 1-5.0 volts so a guess would be 0.01 volt steps which would give a dynamic range of -40F to + 250F and still leave room at top and bottom [for a short {5.000 volts} and an open 0.000 volts to be determined by ecu] .

Since the sensor is only critical at high temps 176-250F and the normal range for ecu [170-215F the 350 to 175 ohm range] is quite easy corrupted by corrosion on the sensor terminals and the harness connector!

One might insert [in series with a lead] a precision water proof [GROUND ISOLATED] variable resistor in the 40 ohm range to trim what the ecu sees or get the sensor spot on as to exact calibration.......assuming it is not already, of course if it reads low the converse would be extremely difficult to design or correct!But I suspect the engineers erred on the high side....the sensor would read a few degrees high.

The problem with an immersion type sensor is it cannot read steam only liquid so when the coolant boils it may revert to 212-230-245F or what ever the coolant boils at! Why the interior temp sensor indicator rises then sudden drops in a severe over heat.