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YOUR RESEARCHNormal coolant temp?
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Replace radiator fans and resistors
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Performed · outcome unconfirmed · Original poster
I recently replaced both radiator fans and resistors.
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Suggestion
They also talked about some design changes, although personally I think it's due to the engines not being up to temp and/or not being driven enough after coming up to temp (or driven hard enough) that causes a lot of our issues.
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Suggestion
They also talked about some design changes, although personally I think it's due to the engines not being up to temp and/or not being driven enough after coming up to temp (or driven hard enough) that causes a lot of our issues.
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Suggestion
If the car is out running hard (up a mountain pass) on a cold day at 70 mph, the rad exit temps could be below 100 deg F, while the engine coolant exit temps would be much higher (around 190 I would think), and at the low rad exit temp, the thermostat wouldn't open.
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Suggestion
Also, if after I stop the car I hear the radiator fans running, I'll let them finished before turning the engine off.
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Well and part of it too, these cars just seem to run pig rich when they first start up and go through the warmup loop.
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Replace although personally i think it's due
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Suggestion
They also talked about some design changes, although personally I think it's due to the engines not being up to temp and/or not being driven enough after coming up to temp (or driven hard enough) that causes a lot of our issues.
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Suggestion
If the car is out running hard (up a mountain pass) on a cold day at 70 mph, the rad exit temps could be below 100 deg F, while the engine coolant exit temps would be much higher (around 190 I would think), and at the low rad exit temp, the thermostat wouldn't open.
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Suggestion
Once the coolant temp approaches the set temp, the thermostat starts to open and let the green radiator flow start, diverting part of the hot flow (on the upper right) after the cylinders/cylinder heads to the radiators.
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So I need some opinions from my esteemed RL colleagues.
I recently replaced both radiator fans and resistors. I've put about 100 miles on the car since. Yesterday I was monitoring the coolant temp via the climate control hack. I was in stop and go (first gear the whole time) traffic for about 30 minutes. The ambient temperature outside was around 85�. The hottest that the car got in that situation was 101�C. I don't believe that the high speed fans ever activated. The low speed fans were on due to the AC running.
What say ye? Abnormal? Normal?
Some may know this but it is worth stating for the noobs:
The temperature gauge is only approximate.
The sensor for it measures coolant flowing INTO the the engine on bank 1.
You really need to know the temperature
after it exits bank 2
(the hotter bank).
The radiator area accumulate lots of debris that you can't see unless you move the a/c condensers out of the way to clean
between
.
There is a useful mod on Rennlist for the engine compartment fan(not coolant!)
The best way to test all this imho is up on a rack with Durametric + an I.R. temp gun engine warm and at low/high revs. Log the data and report back.Tedious and time consuming but...
Without accurate data from specific locations and not knowing if fans are working correctly(Durametric) you could chase your tail.
Normal based on my time spent monitoring and data logging my Boxster's coolant temperature under a variety of ambient temperature and driving conditions.
That the fans on low speed kept the engine "cool" in 30 minutes of 1st gear stop/go speaks highly of the car's cooling system.
Schnell, this is one of the things I doubt. I traced the coolant passages and found that the coolant temp sensor is actually measuring the coolant after it flows through both banks (in parallel). The sensor is located in the middle of the solid red path in this diagram.
https://rennlist.com/forums/996-foru...l#post12576096
IslaTurbine - the high speed turns on at 103 (mine does).
Ahsai - that diagram is great. Also, does the coolant circulate when the car is at idle? I almost wish there was a "flow meter" to indicate such. Placed way up at the radiators (ha).
This is a useful correction to the conventional wisdom by Ahsai.
Obviously there is still something sub-optimal with the circulation/sensing because Jake gives a cryptic comment about using "Epoxy".
Hopefully Ahsai will eventually complete his very useful coolant circulation diagram.Nobody else has produced anything to this standard .Thank you Ahsai !
https://rennlist.com/forums/996-foru...l#post12576096
If you check out the diagram below, you can see the coolant is circulating around the cylinder heads and cylinders whenever the engine/water pump is spinning. At idle the speed will be lower and at WOT the speed will be higher.
When the engine is cold, the coolant only circulates within the engine block to speed up bringing the coolant up to operating temperature. The thermostat is closed so the radiator flow (green) is blocked.
Once the coolant temp approaches the set temp, the thermostat starts to open and let the green radiator flow start, diverting part of the hot flow (on the upper right) after the cylinders/cylinder heads to the radiators. The flow returned from the radiator can now be mixed with the red flow at the thermostat (since the thermostat is open now). The thermostat will sense the temp of the mixed flows and regulate the opening depending on the sensed temperature.
You can see that the coolant sensor is at the return path of the coolant after the cylinders/heads and NOT AFTER the radiators, which returns on the left side to the thermostat.
m96-coolant-flow.jpg
I have no idea what Jake refers to but my guess is the overheated parts are part of the inside of the heads (responsible for cracked heads), which overheats even before the coolant can be sensed by the thermostat/temp sensor.
Looking at this excellent diagram work-
Question-
Is the red path (radiator bypass) formed by the black water pipe that runs next to the oil filter ?
Comment-
Once the red water temp gets to the thermostat set point, the thermostat opens and water can now take a parallel path through the two parallel radiators. Just as this first occured, the exit temp from the heads (highest coolant temp in the engine) was = to the 190 deg (for discussion sake) temp of the thermostat. Thermostat reacts, opening main gateway to radiators.
Once the radiator flow is established, the thermostat now senses cooler water than what is exiting from the heads, since this engine exit water temp is reduced with the radiator water exit temp (much cooler and a larger flow mass), so the thermostat is
not
now setting the flow based just on engine coolant exit temp. It would seem that the effect would be that the water temp exiting the heads could now be higher than before, as the thermostat is reacting to the cooler flow blended with the temp values from head exit ports.
Not wanting to take off on a tangent proposing a solution when there is no problem, but it is temping to think about. If this is the case, then a proper way to control temperature is with another temp sensor(s) that look at head exit temps, takes the worst one, and controls thermostat poppet valve opening % as a direct reaction to coolant exit temps. This would have the added benefit of being programmable to lead the heat buildup based on observed engine cool down rates as a % of opening of the thermostat.
I also would assume that the current design works, since the temp sensor installed in the vehicles today is connected to the red path cylinder head exit temps, which in my car is always around 175 degs, even though the thermostat is supposedly set at a higher temp to open (190F ?), which is itself a bit confusing.
From reading hartech that makes sense. Just a Monday AM armchair guess, and my personal opinion, but it seems that the oil starts to break down when the engine isn't up to temp and the happy pedal is to the floor.
They also talked about some design changes, although personally I think it's due to the engines not being up to temp and/or not being driven enough after coming up to temp (or driven hard enough) that causes a lot of our issues.
No, the red path is formed by the main oil pump (part #1
here
). I left it out so I can show clearly the coolant ports behind it.
The black water pipe (like 3/4" in diameter) that runs next to the oil filter is for the heater core if memory serves.
More or less but two points to make 1) The thermostat opens gradually (before the set temp) so the degree of opening varies as the temp of the coolant. 2) Now that the thermostat is partially opened, the cooler coolant from the radiators also rushes to cool the heads/cylinders immediately (via the pump).
Yes, I think that's what Jake alluded to. Basically shortening the feedback path to reduce the reaction delay. I think it may be ideal if the thermostat can sense the coolant temp that is closer to the heads/cylinders but physically that will require we move the thermostat closer to the heads/cylinders and at the same time crimping the return flow of the radiators.
I think the coolant sensor itself though is already at the right spot for controlling the fuel/air mixture as it reads the coolant temp right after it exits the heads/cylinders.
Yes, as said above, the thermostat starts to open before that set temp and it's not fully open until the coolant temp is higher than the set temp.
Agreed. I always warm up the engine before flooring the gas pedal. I also do cool down drive after a hard drive and not just stop the car immediately.
Also, if after I stop the car I hear the radiator fans running, I'll let them finished before turning the engine off. The worst temp build up is right after the engine is stopped so I try to avoid stopping the engine when it's too hot.
You can get the oil temperature with Durametric. I don't know where the sensor is for oil temperature. Would be interesting if any knows if the Android apps that people are getting to read other things from the car happens to read the oil temperature as well.
That was solved
here
by tapping into the stock oil temp sender signal
You see what the DME sees.
The stock sensor (#21
here
) is combined with the oil level sensor (similar principle as the dip stick). It's a long probe insertedfrom the top of the engine all the way to the bottom of the oil sump so it picks up the oil temp of the oil exiting the main bearings.
No Android app can retrieve that info because you need something like Durametric hardware interface to the OBDII port to access the second K-line. No other generic OBDII reader can do that (they all access the 1st K-line for OBDII data).
BTW, I start to see how an electronically controlled thermostat can improve things tremendously here. Basically you can place the temp sensor(s) at the ideal location(s). The limitation of the mechanical thermostat is you can only place it in one place and it needs plumbing to where you place it so it may not be practical.
But then it will be susceptible to electrical gremlins and may do more harm than good...
Well and part of it too, these cars just seem to run pig rich when they first start up and go through the warmup loop. That, and not to mention any oil that's getting burnt just can't be good for the combustion chamber or anything really.
So someone who doesn't drive the car, and starts it up once a month to let it idle in the winter, gets a great spring morning, starts it up, off to the races, and all the junk built up on the piston causes detonation, some of the crap loosens up, pistons get blowby, and cylinder gets scored.
That's the other half of my Monday morning armchair quarterback guessing.
It's funny though, even if these run a bit hot they are still in the operating temp of a high performance engine.
Ahsai,
I still question how the thermostat is operating in this picture. The coolant exit temperature from the rads is well below the rad inlet temps, which are close to the engine exit temps.
If the car is out running hard (up a mountain pass) on a cold day at 70 mph, the rad exit temps could be below 100 deg F, while the engine coolant exit temps would be much higher (around 190 I would think), and at the low rad exit temp, the thermostat wouldn't open. On your diagram, the green arrow flow (rad exit) is presented to the thermostat to make a open/close decision.
The sensing part of the thermostat (brass tube, spring side) points to the right so it"s submerged in the red flow therrefore sensing the cylinder output temp, until the thermostat opens, at which point its sensing the combined temp of the mixed red and green flows. Basically it regulates the temp of the coolant temp entering the cylinders. The temp sensor reads the coolant temp after the cylinders. Hope that makes sense.
I guess I should've clarified meaning stock gauge or stock solution. I can't afford to give up any space due to the "where do you put your phone", "which cup holder is the best" threads.
