Why is my heat so cold?
01-16-2019, 01:07 PM
#1
Rennlist Member
Thread Starter
Why is my heat so cold?
This is on my 83. When the temperature outside is above 40, the heater is sufficient. But when it gets below that, the inside of the car is so cold. Turning on the fan works for about 5 seconds, and then the air coming out turns cold. So I leave the fan off. It's seems like it is getting too much fresh air from the outside.
Is there any way to control the amount of fresh air coming in? The levers on the control panel only seem to direct the air to the foot area or to the windshield. The temperature slider is on full heat.
Is this normal for the early cars or is something clogged?
Is there any way to control the amount of fresh air coming in? The levers on the control panel only seem to direct the air to the foot area or to the windshield. The temperature slider is on full heat.
Is this normal for the early cars or is something clogged?
01-16-2019, 01:42 PM
#2
Rainman
Rennlist Member
Rennlist Member
might have a clogged core, or the heater valve might have some kind of blockage?
even low coolant level (air pockets) can make a heater core not work great.
mine will light your toes on fire, it's very good.
tip to improve cold weather engine and cabin warm-up...remove the heat shield separating the "heater return tube" from the exhaust manifolds.
the manifolds radiate HOT HEAT which gets picked up by that tube, which carries that warmer water to the water pump for recirculation into the block and eventually heater core.
even low coolant level (air pockets) can make a heater core not work great.
mine will light your toes on fire, it's very good.
tip to improve cold weather engine and cabin warm-up...remove the heat shield separating the "heater return tube" from the exhaust manifolds.
the manifolds radiate HOT HEAT which gets picked up by that tube, which carries that warmer water to the water pump for recirculation into the block and eventually heater core.
01-16-2019, 02:27 PM
#3
Three Wheelin'
Two other facts to consider:
If there has been old coolant left to gather very high voltage within the water/antifreeze mix ( should be 50-50 ), you may need to check to see if corrosion has occurred with aluminum flakes blocking the heater core. Which actually acts as a sort of 'filter' trapping those small flakes which shed from the cooling passages.
Testing the actual amount of stray voltage within the coolant can be done with your probe. I forget what the readings should be, but talking with a tech or referencing this on Clark's Garage will give you the parameters. When the voltage is too high and the coolant has become too old to remain neutral, the charge within helps promote a flaking off of aluminum surfaces within the water jacket. One of the reasons Porsche recommends a coolant change at minimum of every two years, using a phosphate free, safe for aluminum antifreeze endorsed by Porsche.
The second thing to consider is the water pump's effectiveness and the thermostat's correct temp. control, with proper timing of opening and closing. When either of these begins to show their age and yes, 'wear-out', you will not have the correct holding of the temps within their optimum heating and cooling ranges. You did not mention what your gauge is reading. Even in winter, the temp gauge should read very close to the center line. These cars have tremendous heaters in them and have been known to produce some of the best heat among all older, vintage Porsches. When new, many 911 owners saved their precious air coolers and bought 944s to actually produce some heat for their winter duty, thus saving the metal from the rust worm at the expense of their water cooled brothers. I remember many within the local area driving their 944 all year around and their 911s sat in the garage with a cover on them. None of these looked very good after about 7 or 8 years of salt immersion and doing battle with others sliding into them.
Kind of sad really.
Anyway, check those two items. Along with your heater control valve near the firewall, and the slider actuation on the cabin side under the dash and behind the console.
If there has been old coolant left to gather very high voltage within the water/antifreeze mix ( should be 50-50 ), you may need to check to see if corrosion has occurred with aluminum flakes blocking the heater core. Which actually acts as a sort of 'filter' trapping those small flakes which shed from the cooling passages.
Testing the actual amount of stray voltage within the coolant can be done with your probe. I forget what the readings should be, but talking with a tech or referencing this on Clark's Garage will give you the parameters. When the voltage is too high and the coolant has become too old to remain neutral, the charge within helps promote a flaking off of aluminum surfaces within the water jacket. One of the reasons Porsche recommends a coolant change at minimum of every two years, using a phosphate free, safe for aluminum antifreeze endorsed by Porsche.
The second thing to consider is the water pump's effectiveness and the thermostat's correct temp. control, with proper timing of opening and closing. When either of these begins to show their age and yes, 'wear-out', you will not have the correct holding of the temps within their optimum heating and cooling ranges. You did not mention what your gauge is reading. Even in winter, the temp gauge should read very close to the center line. These cars have tremendous heaters in them and have been known to produce some of the best heat among all older, vintage Porsches. When new, many 911 owners saved their precious air coolers and bought 944s to actually produce some heat for their winter duty, thus saving the metal from the rust worm at the expense of their water cooled brothers. I remember many within the local area driving their 944 all year around and their 911s sat in the garage with a cover on them. None of these looked very good after about 7 or 8 years of salt immersion and doing battle with others sliding into them.
Kind of sad really.
Anyway, check those two items. Along with your heater control valve near the firewall, and the slider actuation on the cabin side under the dash and behind the console.
01-16-2019, 09:00 PM
#4
Rennlist Member
Thread Starter
Coolant is definitely bled and engine cooling is working perfectly normal.
Ok did some diagnosing after getting home tonight. Measured hoses with infrared thermometer.
Upper radiator hose 165
Heater hose in 156
Heater hose out 134
So that implies that the flow is impeded. I checked the heater control valve and it wasn't quite open all the way. I adjusted that and will try again tomorrow to see if that improves things. That's if it doesn't snow.
I always use 50/50 phosphate and silicate free coolant with distilled water without exception since rebuilding the engine with new radiator. I cannot speak for previous owners, who may have clogged the heater core. I didn't do anything to that during the rebuild.
Ok did some diagnosing after getting home tonight. Measured hoses with infrared thermometer.
Upper radiator hose 165
Heater hose in 156
Heater hose out 134
So that implies that the flow is impeded. I checked the heater control valve and it wasn't quite open all the way. I adjusted that and will try again tomorrow to see if that improves things. That's if it doesn't snow.
I always use 50/50 phosphate and silicate free coolant with distilled water without exception since rebuilding the engine with new radiator. I cannot speak for previous owners, who may have clogged the heater core. I didn't do anything to that during the rebuild.
01-17-2019, 01:34 PM
#6
Rennlist Member
Thread Starter
Today was a good test. This morning was 21 degrees.
Getting the valve to open just a bit more did the trick. It is now somewhat toasty, but doesn't lite my toes on fire. The vent at the foot well doesn't flow as well as the center vents. I might just leave it as it is. I don't see a way from that pic how to open it up and clean it out.
Getting the valve to open just a bit more did the trick. It is now somewhat toasty, but doesn't lite my toes on fire. The vent at the foot well doesn't flow as well as the center vents. I might just leave it as it is. I don't see a way from that pic how to open it up and clean it out.
01-17-2019, 03:12 PM
#7
Three Wheelin'
Today was a good test. This morning was 21 degrees.
Getting the valve to open just a bit more did the trick. It is now somewhat toasty, but doesn't lite my toes on fire. The vent at the foot well doesn't flow as well as the center vents. I might just leave it as it is. I don't see a way from that pic how to open it up and clean it out.
Getting the valve to open just a bit more did the trick. It is now somewhat toasty, but doesn't lite my toes on fire. The vent at the foot well doesn't flow as well as the center vents. I might just leave it as it is. I don't see a way from that pic how to open it up and clean it out.
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01-17-2019, 05:23 PM
#8
Rainman
Rennlist Member
Rennlist Member
did you reach behind the intake and manually open the valve fully?
if you pull the intake it's really not that hard to do and the valve is cheap to replace if needed.
if you pull the intake it's really not that hard to do and the valve is cheap to replace if needed.
01-17-2019, 07:03 PM
#9
Rennlist Member
Thread Starter
Valve is relatively new. Replaced it when I rebuilt the engine 12 years ago. 
No need to pull the intake to replace it. Although I remember it being quite annoying.
I want to know if there's any way to clean the air box where the core lives. Maybe shoot compressed air up that footwell hole?
No need to pull the intake to replace it. Although I remember it being quite annoying.
I want to know if there's any way to clean the air box where the core lives. Maybe shoot compressed air up that footwell hole?
01-17-2019, 09:15 PM
#12
Rennlist Member
Thread Starter
Originally Posted by V2Rocket
are your dash vents fully open or are they set to the "defrost" (closed) position?
01-18-2019, 11:21 AM
#14
Rainman
Rennlist Member
Rennlist Member
FIFY
get some barb unions and some extra hose length...put the "in" hose (from cylinder head) pointing to a bucket, and hook the "out" hose (to water pump) to your garden hose and let it push water the opposite direction of normal function...you wont believe the rust and **** that comes out into the bucket.
works great on radiators too when you have them out.
get some barb unions and some extra hose length...put the "in" hose (from cylinder head) pointing to a bucket, and hook the "out" hose (to water pump) to your garden hose and let it push water the opposite direction of normal function...you wont believe the rust and **** that comes out into the bucket.
works great on radiators too when you have them out.
01-18-2019, 11:56 AM
#15
Three Wheelin'
^^^^^
THIS ^^^^^
Just be careful with the amount of pressure or you may be separating seams on whatever radiator core ( either heater or radiator itself ) you are flushing.
The leaks will show up later if you push it too far with pressure, right about the time the new coolant starts to show up on your carpeting or mists up your windows......
and it all becomes a 'do-over'
THIS ^^^^^
Just be careful with the amount of pressure or you may be separating seams on whatever radiator core ( either heater or radiator itself ) you are flushing.
The leaks will show up later if you push it too far with pressure, right about the time the new coolant starts to show up on your carpeting or mists up your windows......
and it all becomes a 'do-over'