Running hot and losing oil pressure
12-12-2019, 05:34 AM
#18
Advanced
Thread Starter
It takes around 5 to 10 minutes to get up to what I would expect to be normal operating temperature. It does not heat up faster than normal, sort of pauses for a while then after 20 minutes or so starts to creep up.
Oil pressure falls away about 10 minutes after it has started to sit just under red line. It does come back with revs for a while, but at that point I am heading for home.
Radiator is a Behr unit, about 7 years and 8,000 miles old. It's been flushed and pressure tested.
12-12-2019, 06:43 AM
#19
Rennlist Member
OK- first suspect is your thermostat and the seals- the engine should be up to operating temperature in about 3 minutes and then hold more or less steady. If it takes longer than this it might suggest that the thermostat is not closed and cold coolant is trying to go round the radiator when the coolant is not hot enough and alternatively, when hot some coolant may be recirculating internally [see notes below].
When the motor is operational and up to operating temperature, with the a/c switched off check that both fans are running. Another little test you can do is with the motor warm, take the leads off the sensor on top of the inlet manifold and short the terminals of the two wires- now depress the hood switch and both fans should run.
Some basic input for you about the cooling system.
First of all the temperature as shown on the gauge has some different interpretations. The value derived on the dash gauge is generated from a sensor on top of the water bridge- there are two sensors in that general location- the dash temp is generated from the sensor that is located on the right hand side of the bridge when viewed from the front of the car- I understand that UK engine variants are configured the same as LH drive variants that most of us own. This sensor provides a single channel output and only feeds the dash gauge. The Temp 2 sensor is located on the left hand side of the water bridge, it has two channels that feed the temperature of the water leaving the engine to the LH and EZK modules and should read the same. A stock vehicle cannot read these values, Sharktuner 2 can read these values in real time [FYI]. Both my current GTS chassis and my late 90S4 gave identical running characteristics in that the temperature gauge needle typically sits about two needle widths to the left of the last white line line. The thermostat opens at 83C and is fully open at about 90C. From memory reading from ST2 the operating temperature as defined by the temp2 sensor runs at about 95C. The radiator typically drops the coolant temperature by about 6 to 8 degrees C so if the water entering the radiator reaches a temp of 95C the water leaving the radiator will be about 89C.
The fans are controlled by a separate logic controller that receives temperature info from the sender on the bottom of the outlet tank on the front of the radiator and under normal conditions the fans switch on at 79C. Given the thermostat starts to open at 83C, the water temp leaving the radiator will be around 77C and thus as the coolant temperature starts to increase above those numbers both fans kick in at 79C starting with both fans running on 7.5 volts and progressively increases until the temperature out of the radiator reaches 95C and the water temperature leaving the engine is around 101C which according to my logic is a touch to the right of the last white line which I understand/read to be 100C. Note that some of our friends do not agree with interpretation of this value but it is what I have measured. I can get the temperature to that point when pushing the motor along with the a/c running and ambient temperatures at or in excess of 40C. To get the temperature gauge north of the last white line you would have to be risking jail in the UK if the system is working correctly.
For the thermostat to work correctly the rear seal has to be in perfect condition- if it is not, then some coolant flow will recirculate internally effectively bypassing the radiator and some cooling efficiency will be lost. If the cooling system is working correctly the engine should be up to normal temperature [close to the last white line] in about 3 minutes or so- [this is why the timing belt low tension warning is not activated for 3 minutes]...
The oil pressure at 2k rpms has some relevance but arguably not a lot. A typical fully warm idle with a 20W50 lube oil will be 2 barg at 675 rpms. The actual oil pressure as defined by Porsche is a specific value at a specific rpm but unfortunately I cannot remember the exact figures. The oil pressure on my motor reaches 5 barg at 3k rpms when fully warmed up. In practice the gauge is maxed out at 5 barg and the relief valve pops at 8 barg so once the gauge is at full displacement the actual pressure will be somewhere between 5 barg and 8 barg.and will vary with revs. I thus did not pick up anything remarkable about your oil pressure characteristics.
When the water pump impeller fails the temperature will climb to the red zone and the alarm will go off after about 5 minutes from a cold start or if it happens on a warm motor the needle will climb virtually immediately- clearly that did not happen to you..
Trust the above helpful [and is correct!].
When the motor is operational and up to operating temperature, with the a/c switched off check that both fans are running. Another little test you can do is with the motor warm, take the leads off the sensor on top of the inlet manifold and short the terminals of the two wires- now depress the hood switch and both fans should run.
Some basic input for you about the cooling system.
First of all the temperature as shown on the gauge has some different interpretations. The value derived on the dash gauge is generated from a sensor on top of the water bridge- there are two sensors in that general location- the dash temp is generated from the sensor that is located on the right hand side of the bridge when viewed from the front of the car- I understand that UK engine variants are configured the same as LH drive variants that most of us own. This sensor provides a single channel output and only feeds the dash gauge. The Temp 2 sensor is located on the left hand side of the water bridge, it has two channels that feed the temperature of the water leaving the engine to the LH and EZK modules and should read the same. A stock vehicle cannot read these values, Sharktuner 2 can read these values in real time [FYI]. Both my current GTS chassis and my late 90S4 gave identical running characteristics in that the temperature gauge needle typically sits about two needle widths to the left of the last white line line. The thermostat opens at 83C and is fully open at about 90C. From memory reading from ST2 the operating temperature as defined by the temp2 sensor runs at about 95C. The radiator typically drops the coolant temperature by about 6 to 8 degrees C so if the water entering the radiator reaches a temp of 95C the water leaving the radiator will be about 89C.
The fans are controlled by a separate logic controller that receives temperature info from the sender on the bottom of the outlet tank on the front of the radiator and under normal conditions the fans switch on at 79C. Given the thermostat starts to open at 83C, the water temp leaving the radiator will be around 77C and thus as the coolant temperature starts to increase above those numbers both fans kick in at 79C starting with both fans running on 7.5 volts and progressively increases until the temperature out of the radiator reaches 95C and the water temperature leaving the engine is around 101C which according to my logic is a touch to the right of the last white line which I understand/read to be 100C. Note that some of our friends do not agree with interpretation of this value but it is what I have measured. I can get the temperature to that point when pushing the motor along with the a/c running and ambient temperatures at or in excess of 40C. To get the temperature gauge north of the last white line you would have to be risking jail in the UK if the system is working correctly.
For the thermostat to work correctly the rear seal has to be in perfect condition- if it is not, then some coolant flow will recirculate internally effectively bypassing the radiator and some cooling efficiency will be lost. If the cooling system is working correctly the engine should be up to normal temperature [close to the last white line] in about 3 minutes or so- [this is why the timing belt low tension warning is not activated for 3 minutes]...
The oil pressure at 2k rpms has some relevance but arguably not a lot. A typical fully warm idle with a 20W50 lube oil will be 2 barg at 675 rpms. The actual oil pressure as defined by Porsche is a specific value at a specific rpm but unfortunately I cannot remember the exact figures. The oil pressure on my motor reaches 5 barg at 3k rpms when fully warmed up. In practice the gauge is maxed out at 5 barg and the relief valve pops at 8 barg so once the gauge is at full displacement the actual pressure will be somewhere between 5 barg and 8 barg.and will vary with revs. I thus did not pick up anything remarkable about your oil pressure characteristics.
When the water pump impeller fails the temperature will climb to the red zone and the alarm will go off after about 5 minutes from a cold start or if it happens on a warm motor the needle will climb virtually immediately- clearly that did not happen to you..
Trust the above helpful [and is correct!].
12-12-2019, 07:03 AM
#20
Rennlist Member
12-12-2019, 09:37 AM
#21
Racer
As the temp rises and oil heats up, its viscosity will fall lower and lower,,, as will the oil pressure... Taking the advise of a (trusty) member here, the aim was to clear out gunk from what WAS (I'm happy to say) a stuck lifter(s) and possibly passages. So I intentionally cycled the car thru temps. Normal operating temperature to HOT - several times! Blocking the radiator with a large piece of cardboard I would get the temp way up with about 2 quarts of marvel and some LiquiMoly in the mix. Worked like a charm!!!
As the temp rose there was clear relationship between the the temp and oil pressure. As the temp rose the oil pressure fell, and vice-versa... At one point the Opressure fell to near zero. As the temp normalized so did the OP... Several times. It took a while for the oil temps to fall back to normal mind you. The coolant temps return to normal much quicker and the OP will creep back up.
Bum thermostats are very real. As are bum inner seals. Start from scratch with them.
I think the thing with the temps and running hot might just be as simple as opening the thermo housing (have a new low temp thermo from Roger,,, with new oring and inner seal!!!!! - inner seal is VERY important - temperature will be allOVER the place without it) and button it up. The coolant will NOT run thru the engine and rad properly without a good (and right installed) rear/inner seal... Leave reservoir cap on and spill as little coolant as possible, of course, when changing thermo. Button it up when done and top the coolant off. I'd bet my foot everything returns to "normal" - whatever "normal" means, haha
It's going to be alright!
PS... If you specialist Porsche mechanic did not replace the inner/rear seal and oring in the thermostat housing and then didn't figure out this problem with you,,,, sorry,,,, fire them...
As the temp rose there was clear relationship between the the temp and oil pressure. As the temp rose the oil pressure fell, and vice-versa... At one point the Opressure fell to near zero. As the temp normalized so did the OP... Several times. It took a while for the oil temps to fall back to normal mind you. The coolant temps return to normal much quicker and the OP will creep back up.
Bum thermostats are very real. As are bum inner seals. Start from scratch with them.
I think the thing with the temps and running hot might just be as simple as opening the thermo housing (have a new low temp thermo from Roger,,, with new oring and inner seal!!!!! - inner seal is VERY important - temperature will be allOVER the place without it) and button it up. The coolant will NOT run thru the engine and rad properly without a good (and right installed) rear/inner seal... Leave reservoir cap on and spill as little coolant as possible, of course, when changing thermo. Button it up when done and top the coolant off. I'd bet my foot everything returns to "normal" - whatever "normal" means, haha
It's going to be alright!
PS... If you specialist Porsche mechanic did not replace the inner/rear seal and oring in the thermostat housing and then didn't figure out this problem with you,,,, sorry,,,, fire them...
Last edited by JayPoorJay; 12-12-2019 at 09:53 AM.
12-13-2019, 05:35 AM
#22
Advanced
Thread Starter
Guys - many thanks for your replies especially Fred and JPJ - I appreciate you taking time to respond in such detail - we'll crack on this end and see what we can figure out. Once we have, I will provide an update.
i think the take away point is, check and replace the thermo seals
i think the take away point is, check and replace the thermo seals
12-13-2019, 08:00 AM
#23
Racer
12-13-2019, 08:22 AM
#24
Being it is an automatic, have you checked the front flex plate for any loading?
The symptoms you describe also fits a thrust bearing failure scenario.
Just thought to mention this possibility so everything can be checked off while you are diagnosing this problem.
The symptoms you describe also fits a thrust bearing failure scenario.
Just thought to mention this possibility so everything can be checked off while you are diagnosing this problem.
12-15-2019, 12:07 PM
#25
Rennlist Member
How smoothly does it run, and does it have good power?
Reason I ask is that they can run lean if a bit fuel starved. And that will drive temperature, beyond capability of an operational cooling system.
Been there, done that on an 85 32v car. In this case it was partially clogged injectors. But if one is electrically disconnected that could also cause it.
Telltale, looking back at it, was white coating when looking up into the two exhaust headers after dropping the exhaust.
Reason I ask is that they can run lean if a bit fuel starved. And that will drive temperature, beyond capability of an operational cooling system.
Been there, done that on an 85 32v car. In this case it was partially clogged injectors. But if one is electrically disconnected that could also cause it.
Telltale, looking back at it, was white coating when looking up into the two exhaust headers after dropping the exhaust.
12-23-2019, 03:53 PM
#26
Advanced
Thread Starter
Hi guys
Back and up and running.
It seems it was a combination of factors. Firstly, the louvres were not deactivated. When I dropped it into a spark recently, he innocently replaced fuse 23, so the louvres were working and it took a while for us to twig.
One of the fan switches / sensors was iffy, so it was running warm but not kicking in.
To be doubly sure, the water pump was checked for manufacturing fault (metal impeller), it is a new unit but best to check. New cambelt fitted despite being only 2,000 miles old. for the cost of it, why not fit new and be sure.
Some goo in the rad and block, which was flushed out.
Good clean and using IR / temp gun everything is running hot where it should and cool where it should. Thermostat and seals replaced.
It is running a touch lean, so that might, as said above, add a bit of heat into the equation, and the temp gauge probably could do with replacing as it is likely to over read due to age. Old wiring was chased back with new for that reason.
I also got myself under neath and checked the thing that dare not speak it's name. 3mm of shift so sorted that. Ritech block next I think.... Last checked in June 2018 and all ok, so sensible to double check.
Oil pressure now 5 bar revs hot and 3 bar at hot idle.
Water on top white marker but no more.
A big thank you to everyone who pitched in and helped here, I appreciate your time and my best wishes for Christmas and New Year. My wrench has been a star and put in lots of extra effort and has been reading this to make sure we covered everything. So thank you to him.
Thanks again
Back and up and running.
It seems it was a combination of factors. Firstly, the louvres were not deactivated. When I dropped it into a spark recently, he innocently replaced fuse 23, so the louvres were working and it took a while for us to twig.
One of the fan switches / sensors was iffy, so it was running warm but not kicking in.
To be doubly sure, the water pump was checked for manufacturing fault (metal impeller), it is a new unit but best to check. New cambelt fitted despite being only 2,000 miles old. for the cost of it, why not fit new and be sure.
Some goo in the rad and block, which was flushed out.
Good clean and using IR / temp gun everything is running hot where it should and cool where it should. Thermostat and seals replaced.
It is running a touch lean, so that might, as said above, add a bit of heat into the equation, and the temp gauge probably could do with replacing as it is likely to over read due to age. Old wiring was chased back with new for that reason.
I also got myself under neath and checked the thing that dare not speak it's name. 3mm of shift so sorted that. Ritech block next I think.... Last checked in June 2018 and all ok, so sensible to double check.
Oil pressure now 5 bar revs hot and 3 bar at hot idle.
Water on top white marker but no more.
A big thank you to everyone who pitched in and helped here, I appreciate your time and my best wishes for Christmas and New Year. My wrench has been a star and put in lots of extra effort and has been reading this to make sure we covered everything. So thank you to him.
Thanks again