The "normal" location of the 928's temperature gauge causes a lot of angst
among owners, and not just on this list. I think that it's fair to say that the
928's temperature gauge is inaccurate, but individual gauges usually are
Based on five years participating in online 928 forums, my observation is that the "normal" position for a gauge usually is anywhere between the two large white marks. Obviously, you should satisfy yourself that the engine is not overheating; otherwise, you should take note when your temp needle moves from ITS normal position, wherever that may be. NEVER ignore the temp warning light!
The indicated temperature will rise on hot days in heavy (ie slow) traffic, when you are going hard on the track and if you're going exceptionally hard on the road. My gauge usually sits at the lower white mark, including at high speed, with the aircon on, in ambient temps of over 105F.
As Doug says, the standard 928 has heaps of cooling capacity (not forgetting those 8 liters of oil). If the temp of the thermostat housing is usually in the 85-90 degrees C (185-195F) range, it is right where Porsche intended it to be, so you shouldn't worry, let alone mess with the cooling system to make you feel better about the gauge reading.
'80 Petrolblaumetallic 'S' look
we all know how inaccurate the 928's "living" temperature indicator (gauge) is however this may interest you
For the last nearly two years I have monitored my car's temperatures at various locations using an IR temp. reader which has an accuracy of about +/-2C.
Ambient: Lowest -5C Highest 43C
|Gauge||85||81||87||85||reads about midway mostly|
|Rad hose top||72||55||88||74|
|Rad hose lower||76||61||90||76|
|Vee near sender||88||80||94||88|
|Oil cooler top||74||54||88||75|
|Oil cooler lower||76||53||90||77|
|ATF cooler top||60||43||76||61|
|ATF cooler lower||50||31||77||51|
These figures are the product of nearly 100 IR readings taken over nearly 30000kms and all were taken after a minimum of 50kms had been covered Note that in nearly all cases the average and median are very close suggesting excellent stability within the cooling system
In a well maintained 928 and using a 83C(OEM) thermostat (these open at 83C and are fully open at 98C)it appears that the engine's "core" temperature hovers around the 85>90C mark under most conditions.
People using a 75C thermostat in "normal" use should note the Valve Cover and Vee results above. Lowering these by 8C (75C against 83C) may cause excessive wear in cold ambient temperatures with very little (if any) gain in high temperature operation
The 928 has enormous cooling system capacity when viewed as a system (coolant, oil and air). It certainly needs air flow!
The S4's first overheat warning is at 118C and the "final" warning is at 120C
Oil temperatures are always hard to obtain accurately but when using the correct viscosity synthetic oil up to 130C is not a problem In normal use and going by my readings I think the 928's engine oil hovers around the 85C (the oil cooler thermostat opens at 87C)to 100C range, this is absolutely ideal for long oil and engine life
My vehicle is NOT operated in a City environment very often, however I do live in Tropical Australia
I hope this helps in understanding our cars a little better
yes Chris the only published oil pressure (OP) by Porsche for the 928 that I am aware of is given as a minimum of 5bar at 4000-5000rpm and with the oil (obviously the recommended viscosity) at between 80C-100C
This minimum of 5bar does not tell the true story either. As the oil pressure relief valve opens at 8-9bar (variously) it is possible that using thicker oils may trip the relief valve at higher revs (and also the filter by-pass valve) even in normal day to day use!
It is possible that the actual oil pressure may well indeed be above 5bar and near 6 or 7bar for a lot of the time when using SAE50 oils (say
Low idle OP is really only a worry if it triggers the switch. Always check that the warning light works during start up Very few engine makers (if any) specify an idle OP (see below) minimum any longer - they simply and reliably rely on the sender and light working.
At idle too many variables may apply and the dashboard indicator (gauge) is just that - an indicator. In the 928 of course we have a gauge and a light!
Many years ago (40 or so) MB had the following idle oil pressure requirement for one engine family as follows;
1 - Use a calibrated "Master Gauge"
2 - Oil = SAE10w
3 - Oil Temperature = 100C
4 - Required idle oil pressure = >2bar
Note: At 2500rpm using 1 to 3)above oil pressure= 5bar
So strict controls were applied even then as the idle OP is a difficult parameter to reliably replicate
Many people get confused about OP and perhaps forget that the flow is extremely significant. The oil pump is of constant displacement (it delivers the same amount for every revolution). At idle some circulation losses do occur but the flow of a conforming viscosity lubricant when hot will still leave the pump in the same volume! You may see a lower pressure with thinner conforming oils but remember that the flow (volume) is constant per rev.!
As long as you meet the Porsche specification of 5bar at 4000-5000rpm and the (working) oil pressure light does not illuminate you are meeting Porsche's design intent!
The flow v pressure issue is misunderstood by many - and has been for decades. A more linear flow (as with a viscosity conforming synthetic) does increase the oil's ability to carry away heat and there is less likelihood of opening the pressure relief valve
High OPs are NOT always a good thing - the maker's correct pressures are!
Very high OPs, cold thick oil and high revs. are indeed a good recipe for damaging engine bearings. This is due to the hydrodynamic "wedge" affect in this individual area of engine lubrication. In these circumstances too of course the oil will be likely flowing back to the pump via the relief valve and by-passing the oil filter
As Mark is very well aware, racing a 928 represents another scenario altogether - this post does not cover that situation!
I hope this is of some interest