No heat... not sure what to check next.
01-13-2018, 10:30 AM
#16
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Ok. With a static idle test that makes sense. In a winter-cold garage it can be difficult to get the engine to 185+.
Could always start by throwing that away and putting the correct one in, since about the only thing it can do is screw up your static test. But, either way, 160 degree water should be plenty warm if it is actually flowing.
Assuming that air flow isn’t blocked, sounds like the next thing is DrB’s core flow test. Checking the port for occlusion with the equivalent of a bent stick will be easy to do at the same time.
With some of the other stuff installed on the car, I'd venture a guess that it's got a lower temp T-stat from one of our vendors.
Assuming that air flow isn’t blocked, sounds like the next thing is DrB’s core flow test. Checking the port for occlusion with the equivalent of a bent stick will be easy to do at the same time.
01-13-2018, 10:40 AM
#17
That's the piece of the puzzle we needed. It actually sounds more like a stuck open t-stat at that temp. My 79 was like that when I bought it, would never get much above 160F. Even at the track it took several laps at speed to see any movement on the temp gauge.
One test, disconnect the fans and see if the temps start to rise.
One test, disconnect the fans and see if the temps start to rise.
Ok. With a static idle test that makes sense. In a winter-cold garage it can be difficult to get the engine to 185+.
Could always start by throwing that away and putting the correct one in, since about the only thing it can do is screw up your static test. But, either way, 160 degree water should be plenty warm if it is actually flowing.
Assuming that air flow isn’t blocked, sounds like the next thing is DrB’s core flow test. Checking the port for occlusion with the equivalent of a bent stick will be easy to do at the same time.
01-13-2018, 10:50 AM
#18
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Pretty sure it is a double pass heat exchanger where the header tank is divided into two chambers so coolant is forced to flow over to the other header then back to the exit. Other wise it would never opt to go through the core as it would simply follow the path of least resistance.
01-13-2018, 11:00 AM
#19
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01-13-2018, 01:34 PM
#20
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Not to start a "which" thermostat war but the lower temp 75C - 928 106 129 16 is stock on 87 to 89 USA cars.
The higher temp 83C was used from 90 to 95.
Pre 87 cars had the option of either.
8>)
The higher temp 83C was used from 90 to 95.
Pre 87 cars had the option of either.
8>)
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
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928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
01-13-2018, 01:37 PM
#21
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Long shot - what position is the re-circulation flap? If it is closed/failed in the down position very cold ambient air is being introduced into the system which can negate the hot air flow.
01-13-2018, 01:47 PM
#22
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What about getting a contact temp reading of the core through the vent?
01-13-2018, 02:06 PM
#23
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It defaults to the down position as opposed to up against the firewall (recirc. position).
Major issue in the hot time of year and the main culprit for decreasing the effect of good AC. At that time it needs pushing up and away to seal at the firewall.
Thinking about it same applies - ambient hot or cold. So reach under the passenger side glove box/parcel shelf and stick fingers through center of grill.
Push flap up and away from you and then push anything in there to make it stay in that position. Or fix the recirc. actuator.
Major issue in the hot time of year and the main culprit for decreasing the effect of good AC. At that time it needs pushing up and away to seal at the firewall.
Thinking about it same applies - ambient hot or cold. So reach under the passenger side glove box/parcel shelf and stick fingers through center of grill.
Push flap up and away from you and then push anything in there to make it stay in that position. Or fix the recirc. actuator.
01-13-2018, 04:26 PM
#24
Recir flap is closed. That's the default unless set for full cold.
01-13-2018, 06:37 PM
#25
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Recir flap is closed. That's the default unless set for full cold.
01-14-2018, 03:45 PM
#26
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Some observations:
1. The coolant temperature of 160F [71C in proper units] is suspicious as with a 75C thermostat the coolant temperature should be at least that value so as stated earlier is the thermostat closing correctly? Does it take a long time for the engine to warm up or better still, is it even reaching normal operating temperature? If the thermostat rear seal is not seating correctly for sure that will not help matters in cold climes.
2. Is there any possibility the a/c solenoid is kicking in?
3. If the temperature drop across the heater core is only 10F then that would seem suspicious. At the very least this suggests coolant is flowing but not having much heat taken out of it. What temperature is air coming out of the central vent at [I would expect to see about 140F to 150F]? Whatever the return coolant temperature, the air should be able to reach to within about 10 degrees F of that temperature if the matrix is not clogged up.
4. If the recirc flap is not closed then heating cold air will not help. Better to heat warmish air than air at 32F.
1. The coolant temperature of 160F [71C in proper units] is suspicious as with a 75C thermostat the coolant temperature should be at least that value so as stated earlier is the thermostat closing correctly? Does it take a long time for the engine to warm up or better still, is it even reaching normal operating temperature? If the thermostat rear seal is not seating correctly for sure that will not help matters in cold climes.
2. Is there any possibility the a/c solenoid is kicking in?
3. If the temperature drop across the heater core is only 10F then that would seem suspicious. At the very least this suggests coolant is flowing but not having much heat taken out of it. What temperature is air coming out of the central vent at [I would expect to see about 140F to 150F]? Whatever the return coolant temperature, the air should be able to reach to within about 10 degrees F of that temperature if the matrix is not clogged up.
4. If the recirc flap is not closed then heating cold air will not help. Better to heat warmish air than air at 32F.
01-15-2018, 07:13 PM
#27
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The diaphragms are all holding vacuum, so I think they are fine. The flap is closed so it's pulling in cabin air.
I've been running the same thermostat I purchased from Roger for the past 3 years, and I had VERY hot heat this summer when my AC was not working... something happened in the last few months that's not allowing air to pass over the heat exchanger (or the heat exchanger is in fact, not flowing enough). when the heat is on. I have serious doubts it's the thermostat. The car gets up to temp in about 5 minutes or less in the winter.
AC solenoid is not kicking in. I can hit the switch and get a noticeable change in RPM's when it's running.
I'll do the flow test Dr. Bob recommended and see what I find. Sean told me what the OD of the inlet/outlet ports were on the core, but I can't remember. I need to buy a couple feet of clear tubing and a garden hose adapter, so getting the diameters will help me get what I need.
I've been running the same thermostat I purchased from Roger for the past 3 years, and I had VERY hot heat this summer when my AC was not working... something happened in the last few months that's not allowing air to pass over the heat exchanger (or the heat exchanger is in fact, not flowing enough). when the heat is on. I have serious doubts it's the thermostat. The car gets up to temp in about 5 minutes or less in the winter.
AC solenoid is not kicking in. I can hit the switch and get a noticeable change in RPM's when it's running.
I'll do the flow test Dr. Bob recommended and see what I find. Sean told me what the OD of the inlet/outlet ports were on the core, but I can't remember. I need to buy a couple feet of clear tubing and a garden hose adapter, so getting the diameters will help me get what I need.
