Re: Can't you read the coolent temp from the climate control panel?

I have a right front radiator leak. Since I'm bringing my 62K 1998 986 in for radiator replacement I thought it would be a good time to install a low temp thermostat and maybe a couple other important parts that fail over time. I was thinking of having the mechanic put in a Vertex rebuilt water pump and front motor mount. Would this be wise or wasteful? Any other thoughts on good items to replace while this repair is happening? Thanks! Aaron

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AaronInIowa
I have a right front radiator leak. Since I'm bringing my 62K 1998 986 in for radiator replacement I thought it would be a good time to install a low temp thermostat and maybe a couple other important parts that fail over time. I was thinking of having the mechanic put in a Vertex rebuilt water pump and front motor mount. Would this be wise or wasteful? Any other thoughts on good items to replace while this repair is happening? Thanks! Aaron

at the idea of this.

They want to know why?

They remind me -- I already know this -- the T-stat is there to help warm up the engine quicker. Once up to temp the engine coolant temp is controlled by ambient temp, how the car is being driven, and how much cooling capacity the car has.

When Porsche wants to improve a models' cooling it adds cooling capacity, for instance for an S model or a Tip equipped model Porsche adds a 3rd radiator. Also, some changes are made to the fan speeds.

I posted the data from a chart that shows in 60 hours of run time for a given engine operating temp how engine wear is very high at colder temps and only starts to drop to while still not insignificant levels it at least drops off some at higher temps.

At 70F in 60 hours cylinder wear is 0.008" and fuel consumption is 3.8GPH.

At 180F in 60 hours cylinder wear is 0.0005" and fuel consumption is 2.9GPH.

At 210F cylinder wear drops to 0.0003" and fuel consumption drops to 2.8GPH.

Now while even 0.0003" is a very small amount of wear, it is "huge" compared to the wear allowance the cylinders have. Generally piston/cylinder wall clearance is around 0.001" or thereabouts. Any more than this and the engine will be noisy (piston slap) and suffer from increased blow-by.

I do not know what the max. cylinder clearance/wear allowance is for Porsche engines but I rebuilt a Dodge pick up truck engine and the clearance was around 0.004" to 0.005" and this was at the upper end of the allowed clearance. I didn't have the money to rebore the cylinders and buy oversized pistons. So I honed the existing cylinder bores and bought new standard sized pistons and rings.The engine to my surprise ran quite well. But it wasn't asked to rev to 7200 rpm. Its redline was around 5K and I never ran the engine even that high, what with an automatic and limited freeway driving.

My point is there is really no acceptable wear rate.

For example my Boxster with over 256K miles has 8533.33 hours of run time and even with all this run time still runs very well and has not as best I can tell experienced any significant cylinder/piston wear.

Thus the wear is down in the sub-nanometer range. I mean we're talking a fraction of an atom's width.

Also, and this is very important, it has accomplished this with at times being driven in ambient temp and driven in such a manner the coolant temp has climbed to 226F and remained there for sometimes hours.

Let me make this clear. 226F coolant temp doesn't require 116F ambient temp (though this was one such case) to happen. I have managed to get the coolant temp -- on purpose -- to 226F driving the car very hard in the mountains on even a mild day. Or even simply driving in heavy traffic, stop/go driving, fast through drive through idling (with the A/C off of course) the engine while waiting for the line to move.

Leave the low temp t-stat on the parts shelf would be the techs' recommendation and I can only second this.

Sincerely,

MarcW.

Amazing info. The low temp t-stat begins opening at 160, but based on your data, there is no reason to suggest this will help reduce engine wear and could quite possibly do the opposite. Thanks! Based on the leak though, do you agree it would be worthwhile to replace tstat, water pump, and motor mount given vehicle age and history of a leak? I am concerned about the leak allowing air in the cooling system and prematurely aging my pump.

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AaronInIowa
Amazing info. The low temp t-stat begins opening at 160, but based on your data, there is no reason to suggest this will help reduce engine wear and could quite possibly do the opposite. Thanks! Based on the leak though, do you agree it would be worthwhile to replace tstat, water pump, and motor mount given vehicle age and history of a leak? I am concerned about the leak allowing air in the cooling system and prematurely aging my pump.

until the coolant temp climbs to 212F (and shuts the fans off at 205F). Even at 212F the fans are only on low speed. If the temp climbs to 216F the fans are switched to high speed.

My info is that at lower continuous operating temperatures engine wear increases.

Fix the radiator leak. That is replace the leaking radiator. The risk is not from air being introduced into the system but the system being unable to maintain pressure will then allow hot coolant to flash to steam creating localized overheating in the engine with possibly serious engine damage as the result.

If you do nothing else -- other than replace the obviously leaking radiator -- be sure the cooling system is properly refilled with the correct anti-freeze/distilled water mix and that no air pockets exist.

If the leaking radiator was leaking due to corrosion you probably should consider replacing the other side's radiator.

And if you consider this you need also consider both A/C condensers which are suspect since they sit in front of their respective radiator and are subject to the same corrosion damage as the radiators (from build up of trash that collects moisture) thus a case could be made to replace these as well, but this starts to run into some money, although to get to the radiators the condensers have to be moved out of the way (though not disconnected from the lines).

If the condensers are replaced the A/C lines of course are disconnected and the refrigerant/compressor oil has to be removed first then replaced after the new condensers are installed.

I do not know what this costs in parts, labor or supplies (refrigerant/compressor oil).

Check the water pump for any signs of leakage (wetness) and the pulley/shaft for any play.

Check the belt for a sharp edge. A sharp edge suggests the belt is not tracking properly and this can arise from a worn water pump bearing.

If you replace the water pump replace the t-stat. I was taught to check the new t-stat in a pan of hot water -- on the stove -- with a thermometer to verify the t-stat opens at the right temp and opens fully to avoid using a defective t-stat or one that is mis-marked.

If a t-stat is not opening fully the coolant lines to the radiators will be cooler than they should be. If the t-stat is stuck open the engine takes longer to warm up and with the A/C on (the fans running) the coolant temp can drop as coolant loses too much heat and the t-stat fails to (partially) close.

You can't go buy the in-dash temp gage/needle.

You need a way to read the coolant temp in real time to know what the coolant temp is.

Sincerely,

MarcW.

I copied this from another forum..... I haven't tried it... but this was quite the buzz many years ago on the old PPBB:
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From Ferd - Thanks!

Porsche AC Diagnostics
(undocumented, unsupported feature)

The AC Climatronic unit is actually manufactured by Audi. There is some sort of serial data stream (not CAN) that allows the AC unit to display engine parameters. This works on 1997-2000 boxsters. Same as 996....

To switch from F to C:
Hold down the recirculating button then push both the temperature + - buttons.

To access diagnostics:
Hold down the Recirculating & Air up buttons for 5 seconds. The + - buttons go up and down through the list of "c" codes. The center vent button switches the left display between the "c" code and its actual value. Press the Auto button to exit.

I have yet to verify all these, this info was copied from wonderful people on PPBB!
Here is a list of what can be seen:


0c - ERL
1c - Oil Temp?
2c - Inside temp. Sensor mounted in the aspirator assembly at the side of the dash.
3c - Outside temp. Sensor located inside the air inlet of the A/C unit.
4c - Outside temp. Sensor located in front grill of the radiator. The data is fed to the Climatronic from the instrument cluster. When not moving, the instrument cluster OBC temp display retains it's last setting until moving. This is to prevent heat emanating from the radiator affecting the temperature sensor. The A/C unit uses the lower of the two outside air temp values in determining fresh-air temp.
5c - Outside temp. (matches OBC outside temp display)
6c - Coolant temp.
7c - Footwell discharge temp.
8c - Sun sensor (dash top)
9c - Sun sensor.
10c - Passenger compartment fan speed.
11c - Passenger compartment fan voltage.
12c - Temperature mix Flap command 1=COLD, 100=HOT
13c - Temperature mix Flap position
14c - Central Flap command
15c - Central Flap position
16c - Footwell/Defrost Flap command
17c - Footwell/Defrost Flap position
18c - Recirculation Valve command 1=OFF, 100=RECIRC
19c - Recirculation Valve position (feedback)
20c - Vehicle speed in kph, updating only once per second. (real speed, not speed+safety margin as in the speedometer)
21c - Engine RPM in hundreds. This too only updates once per second.
22c - ?
23c - ?
24c - Sun sensor, exterior lights switch & panel lights control (term. 58 & 58d voltage) - used for A/C panel display illum.
25c - ?
26c - ?
27c - ?
28c - Fan speed?
29c - ?
30c - Engine run time in seconds (255 max.)(=0xff)
31c - Timing counter
32c - Displays test
33c - Software version? Mine states 3.4
34c - ?
35c - Outside temp. from inlet sensor (filtered?)
36c - temp?

In some MYs, yes. But not all. Not in my 02 Boxster for instance cause I tried it.

Sincerely,

MarcW.

Cold is cold. Oil is too thick and the parts are nto at operating temp and therefore not at design size - they dont fit together correctly. This is a very bad situation and is why we should all run cars very easily until warmed up.

Operating temp probably has a wide range, any only porsche knows the specs. But in this range you have the best fit, oil is sufficiently viscous, and wear is very, very, very low. Stupid low. Full hyrdodynamic float for all surfaces.

Hot is above the point at which the parts begin to again not fit properly, and the oil begins to fail hydrodynamic lubrication under high stress. This may be only for a few instants, points in a piston's cycle or a bearing's spin. But it happens. When things are this hot, as marc noted, the t-stat is out of the picture. Its wide open and you are limited by radiator capacity, airflow, fans, etc. but we can all rest assured the water is above 160- degrees and many internals of the motor are likely above 350 deg (F). Oil is likely climbing above 250 deg. This is where wear again begins to accelerate. I assume, though i do not know, that those curves DO accelerate - they are likely parabolic ( and on the ascent wise guys).

This is why i keep harping on oil that flows well at low temps for some conditions, and resists shear-down for others, and claim that there is no "perfect" oil, merely a series of trade-offs. That's why racers in S. Florida of Dominican origin run 15w50 and its the right decision, while others may be better with 5w30 . Neither meet Porsche's spec.

Grant

Grant

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