This one'll stump you all.......

[rabbitman]

So I've never had a good heater in the rabbit, it'll blow "warm" all winter but never HOT except in summer. Lots of new t-stats, 3 new heater cores and numerous times of taking the heater box in and out trying to find ANY problem with it. The engine DOES get up to temp, verified several times using different methods.

Outside temp is -35F. If I start it and idle WITHOUT the heater fan on the engine will get fully up to temp within a half hour.

However, same outside temp and same idle time but if I turn the fan on LOW the engine will never get hot. Even driving it with the fan on low makes it hard to heat the engine up and if I idle it up to temp and then turn the fan on the engine will cool right down.


So the heater system IS removing lots of heat from the cooling system, but why is the air not hot?

Remember, this is MK1, there are no hot/cold air mixing flaps inside the heater box, it's all controlled by a valve in the heater hose.

Any takers?

[R.O.R-2.0]

its gotta be sucking cold air from somewhere.. does your heatercore have the foam gaskets on the sides/bottom of it to keep the air from blowing around it?

how hot is your t-stat?

i recently put a 190* t-stat in my car, and the heater works MUCH better now..

[8v-of-fury]

BECAUSE ITS F****** MINUS 35 DEGREES FAHRENHEIT!!!

Your cooling system is just ridiculously efficient, that is all. RIDICULOUSLY. so much so that the tiny radiator that is the heater core, has the ability to fully cool the motor.

At those temperatures, i really doubt the engine ever actually gets to the point that the thermostat opens.. unless you have a very low degree thermo in there. Which is why you can maintain steady higher temps with the coolant valve shut for the heater core.

As soon as you open the heater core valve it is allowing the now freezing cold cabin air to take the not so hot air from the coolant.

The air is likely not hot because your body is too damn numb to tell the difference..

[burn_your_money]

Are your side vents fully closed? Those never get hot air. That foam around the heater core is also very, very important.

[AudiVWguy]

What happens if you completely cover up the radiator. You can always keep an eye on the temp gauge just in case. You know how you see the semi's have those custom covers oner their radiators. Then letting more air pass thru till it's right on the temp gauge.

[R.O.R-2.0]

Are your side vents fully closed? Those never get hot air. That foam around the heater core is also very, very important.

x2 on the side vents.. they are just straight outside air..

forgot about them for a sec, thanks for the reminder Tyler!

[8v-of-fury]

What happens if you completely cover up the radiator. You can always keep an eye on the temp gauge just in case. You know how you see the semi's have those custom covers oner their radiators. Then letting more air pass thru till it's right on the temp gauge.

It wont matter to the coolant unless the thermostat has opened. However at cruising speed it will help cold air from blowing across the motor.

I love the cold air vents.. they are my favourite mk1 feature

[ORCoaster]

8V,  you have me busting a gut here.  Too numb to tell the difference?  I'd say so.  

Having a heater that doesn't crank the heat is so non-VW.  I get heat out of the defroster within 3 blocks of the house after startup.  At the temps you have going there I think the heater core is indeed working like the radiator.  Do you block the radiator off in these kinds of temps.  You should, cardboard, a vinyl flap, something, think like a trucker.  On second thought, no don't do that, they are a nasty bunch.  But do block the rad.

You say you have put in several t-stats.  Temp ranges?  I run the 190 degree one and that is hotter than the one that came in it a year or so ago.  

I didn't see where you have checked the water pump for a free spinning or poorly functioning vane in there.  Pumping that hot water into the core is kind of critical.  

I must say getting a car running in that temp has to be an art.  My sympathies.  We had cold on the coast, 30F and even being bundled in coveralls I sissied out working on the timing as my hands wouldn't hold the wrenches anymore.

[R.O.R-2.0]

What happens if you completely cover up the radiator. You can always keep an eye on the temp gauge just in case. You know how you see the semi's have those custom covers oner their radiators. Then letting more air pass thru till it's right on the temp gauge.

It wont matter to the coolant unless the thermostat has opened. However at cruising speed it will help cold air from blowing across the motor.

I love the cold air vents.. they are my favourite mk1 feature

all mk2 cars got them also, buddy..

[8v-of-fury]

What happens if you completely cover up the radiator. You can always keep an eye on the temp gauge just in case. You know how you see the semi's have those custom covers oner their radiators. Then letting more air pass thru till it's right on the temp gauge.

It wont matter to the coolant unless the thermostat has opened. However at cruising speed it will help cold air from blowing across the motor.

I love the cold air vents.. they are my favourite mk1 feature

all mk2 cars got them also, buddy..

no they didn't? I have yet to see an mk2 that has the cold air vents.. yours were all A/C maybe that makes a difference? I have a 90 wolfsburg built jetta. Heat comes out of all the vents in the car. Window, feet, and passenger vents.

[AudiVWguy]

Think like a trucker. +2
I think I'm running a 92C T-stat.

[R.O.R-2.0]

Think like a trucker. +2
I think I'm running a 92C T-stat.

87c is 190*f

92c is 200*f

[Luckypabst]

How's your electrical system? My van would magically 'cool off' depending on electric load, such as fan motor, headlights, etc...

Chris

[AudiVWguy]

That's why it reads 203-5 at the coolant coming out of the head.

[8v-of-fury]

That's why it reads 203-5 at the coolant coming out of the head.

That is beauty for keeping a diesel warm in the winter.