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Discussion Starter #1
Hi all,

Over the last few weeks (as the weather gets colder) I`ve noticed I have to set the heating in my car a few degrees warmer than usual to keep the car sufficiently warm so I thought "time to flush the heater core....."

Having read as much as I could find on the heater core/coolant system flushing etc I had a stab at flushing the heater core out.

First off, I drained the system, there were a few bits/particles in the bottom of the (yellow) bucket I used to catch the old coolant but nothing to really write home about, so on I plodded.

I attached 2 of those washing machine/dishwasher drain hoses to the barbs of the heater core and put the other end of one in the (now empty) bucket and blew.... again some crap came out but not a great deal, I swapped them round and blew the other way and the same, just a little bit of crap.

I waited a while for the core to fully cool and started flushing it back and forward with tap water from a garden hose while letting the outlet collect in the bucket.... there wasn`t really any more coming out so I blew thru the hoses again and cleared it out.

I then poured in a 250ml bottle of radflush INTO JUST THE HEATER CORE and tied the hoses up out of the way to let the rad flush do its stuff for a while before I decided to agitate it back and forth by blowing 1st one way, then the other to make sure the fuid went everywhere inside the core, I did this for around 10 minutes before leaving it to settle for a further 15 minutes and then flushed it out with the garden hose.

I refilled the system with just tap water and ran the engine to operating temp but couldn`t get anything to come out of the weep hole on the heater core barb so I popped the hose off and there was only a little trickle coming thru the core so I drained and refilled another 3 times (over the course of the day, letting the engine cool off before refilling with cold water) and there was no change. The slow trickle through the core was warm but as there wasnt really a great deal flowing thru, inside the car didn`t really get toasty hot.

I even tried with the header/expansion tank raised... no difference.

So, I thought it was because there was no real load on the engine and went for a spin, still only a little trickle, only hotter.

As it got hotter I thought I`d squeeze the radiator hoses to make sure there was no air trapped in the system and noticed while the top radiator hose was hot, the one going from the rad to the metal hose that runs across the top of the engine and also seems to feed the turbo coolant, but the bottom rad hose was cold. I don`t mean cool, or cooler, I mean it was stone cold as in no coolant circulating through it. Ah right, Thermostat I thought! so went and bought a GENUINE VAG THERMOSTAT and popped it in. thinking that was that I dumped in the two new bottles of G12 and topped off with water squeezing hoses as I went.

So now, with the new stat, new coolant and all freshly flushed I ran the engine up to temp and tried to bleed the air out of the weep hole, still nothing. Again I popped the hose off the heater core barb and no longer was it a slow trickle, it was a good old flow!! Still nothing from the weep hole though... :confused::confused:

The problem is, the bottom rad hose (runs from the thermostat housing to the bottom of the rad where the hose from the header/expansion tank fills the system and there is also a temperature sensor there) is still stone cold, as in there is no coolant flowing through it..

The heat in the car, seems to be back to more or less how it was, probably helped by the extra flow of water through it with the new stat now opening properly.

My main concern is this bottom hose staying cold, it is staying cold, not cool. The car starts and runs up to temp normally, it runs and performs well, temp on the guage reads bang in the middle on 90 degrees, never over, never under (except for when warming up) and in general it never skips a beat. Oil and filter services every 5000 - 6000 miles, new plugs every 2x oil services.

Engine is a UK 1.8T AWT 150BHP standard manual 5 speed transmission.

Sorry for the long war-and-peace style post but I`ve tried to cover everything I can think of, that said, there`s bound to be something I`ve missed.....:lol:

So, does anyone know why this hose stays cold while everything else seems to be fine?

Please??? Anyone??:confused:

Thanks
 

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Have you ever replaced the water pump? Sounds to me like the WP might be shot...
 

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Discussion Starter #3
Hi,

water pump was replaced around 98,000 miles alongwith the cambelt with genuine VAG parts car is on about 146,000 miles now.

Suppose it could be due another, but i can't bring myself to do the wp/cambelt myself yet. I had the last one done for me at 98,000 miles as I'd just bought the car and couldn't find anything relating to the belt in the service history. I'll have to do it one day....

Would i still be getting good flow through the core if the pump was dead?
 

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You'd be overheating if your WP was dead. Once it's up to temp, carefully pull the small return hose to the top of the coolant expansion bottle to verify flow (or just look at it if your bottle is transparent enough). Flow=WP function. Also, you flushed water through the heater core, so we know it is not blocked. I suppose there could be blockage in the coolant hoses leading into the core, try a long flexible brush and shove it down inside those hoses to see if you can clear something out of there. Alternatively, drain your good fresh mixed G12 coolant into a clean bucket, fill with water and coolant flush chemical to clean out buildup in the engine and other lines, rinse with water, and refill with your G12.
 

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Discussion Starter #5
yeah, i can't see it being the pump either, although there is only flow coming from the return to the header tank when i squeeze either of the rad hoses.

looks like it's another coolant drain, think i'll check the hose from the stat housing to the rad. I drained the coolant by removing the temperature sensor so i couldn't tell if any came from the hose/stat housing or from the rad or just from the header tank.

what are the chances that the rad, or part of it is blocked, what symptoms would i expect to see from that?

Also will the stat only go in one way? is there any chance that i've put it in the wrong way? i put the new one in the same way the old one came out.

Thanks
 

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The top radiator hose is the hot coolant flowing into the radiator. The bottom radiator hose is the cooled coolant flowing out of the radiator. Flow through the radiator loop of the system is controlled by the thermostat. Flow through that loop will be restricted by the thermostat to whatever is needed to keep the engine coolant from getting hotter than the thermostat rating. Depending on how much heat the engine is generating (load related), how cool the ambient air temp is and how much airflow is going through the radiator, that bottom hose isn't always hot.
 

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Discussion Starter #7
Ok, that makes a bit more sense now.

just to be clear though, the bottom hose feels so cold to the touch that I'd say that there is never any coolant actually flowing through it, there is coolant in it as when I squeeze either hose i can see coolant shooting out of the return hose into the header tank.

So far i have been both driving it normally and been on a spirited slightly-more-than-the-speed-limit run on my own personal test track;) and even after a good run under load that bottom hose is stone cold to touch and squeeze. Ambient temp is around 7 to 10 degrees celcius.

Going from what Steve in chicago said, that would mean that the hot coolant runs into the top of the rad and comes out the bottom cooler and then hits the stat which, depending on coolant temp is either closed for cool coolant or open for hotter coolant so surely that bottom hose should be at least warm at some point!?!?

Thing is, i don't know how long before i started flushing etc it's been like this, since I've had the car (around 4 years or so) it's never run hot or cold, only recently has the heating started not being so hot, it certainly wasn't no heat at all cool though.
 

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Discussion Starter #8
OK, just a little update.

Heat in the car, like a blast furnace!:D

Bottom rad hose, still stone cold:thumbdown

Both top and bottom hoses have pressure in them when hot. Not hard to squeeze pressure, but I can feel a difference between when hot and running and when cold and not.

Just for the record, no oil in coolant or coolant in oil, that I can see at least.
 

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Going from what Steve in chicago said, that would mean that the hot coolant runs into the top of the rad and comes out the bottom cooler and then hits the stat which, depending on coolant temp is either closed for cool coolant or open for hotter coolant so surely that bottom hose should be at least warm at some point!?!?
[Deleted bad info!] Yes, that is the correct path. I suppose it's possible that the radiator is doing its job quite well and cooling the coolant so that the bottom hose is cool to the touch. I would expect to feel some warmth there when the engine is at operating temp, not ice cold like you are describing. Sounds like you've got your heater core issue resolved though, and if the engine is not overheating then the radiator must be doing its job!
 

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Are you sure?

On mine, the stat is more-or-less directly behind the water pump and then that hose goes down to the bottom of the rad:confused:
My bad, you're exactly right. Brain fart - bad info deleted in previous post. I checked my bottom hose coming off the radiator after a 5 mile highway drive in chilly (45 deg F) weather and it was cool to the touch, not ice cold, but cool.
 

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Discussion Starter #12
45f, that`s around 7.5c right!?

pretty similar to what we`ve had here, I`ve done about 170-ish miles today and although ambient temps did range from 38f to 48f along the way, at a few points throughout my trip I`ve 'groped' that bottom pipe and again it`s been cool.

I think until I see some problems I should just chill. Still no sign of guage temp fluctuating and I can still get burns from the heating so it`s all good.
 
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