heater bypass valve

[borarob 0]

hi guys, need some wisdom from somebody!

 

what does the heater matrix bypass valve actualy do! I know its function is to stop your heater matrix popping and dumping boiling coolant on you but how exactly does it achieve that?

 

reason I ask is that I currently have cooling problems with my 1.8 valver. I have currently put this down to a knackered fan and motor - it comes on when it should but doesn't do a lot (just makes a racket). anyway today on the way to work car gets very hot in traffic - up to 110. So i thought right use the old trick I used to do in other cars of whacking the heating and blower on full. now this worked for roughly five seconds, after that no heat just cold air.

 

what I'm hoping is that this was just a symptom of the bypass valve actually doing its job, i.e. things are getting too hot, risk of exploding matrix so it closes and diverts hot coolant away from it. Hence my original question...

 

so am i right or do I need a new bypass, valve, matrix, etc etc.

 

p.s. did a search on over heating and a few peeps say replacing expansion cap may help - mine does seem a pants as I have had to tighten it up on more than one occassion - do you think this may help?

 

ta muchly!

[davidwort 0]

it's just a pressure relief valve from matrix inlet pipe to the matrix outlet pipe, to prevent the matrix bursting if it gets blocked, nothing to do with temperature.

 

I'm not sure exactly why the header tank caps changed, I don't think it's anything to do with how they screw in place, more to do with the reliability of the pressure relief they are supposed to give, although I see plenty of old VW's running on the old black caps with no problems.

 

from playing with a couple of valvers recently the radiator mounted switch for the two fan speeds and the thermostat itself seem the most common problem areas, if fan speed 1 is never switched on then it will get up to near 110 onj the gauge before speed 2 finally comes on and brigs the temps down.

[borarob 0]

if thats the case, what do you think my problem is?

[davidwort 0]

try removing the matrix from the system alltogether and connecting the inlet and outlet hose together with some copper pipe or something, also removing the by-pass valves, it could be that the matrix is partially blocked and the valves are releasing enough pressure but not allowing a good flow of water in the system somehow, the sytem is designed to have a free flow of hot water through the matrix at all times, regardless of if your controls are set to hot or cold in the cabin, not sure if this possibly restricts the flow in the whole system if totally blocked though.

 

You need to check your fluid level is right, that your hoses all have water in (i.e. no air locks) and the thermostat and fan switch are operating correctly, usually it takes about 10 minutes from cold with the car idling for the stat to open and the bottom rad hose to get hot, probably another 5 minutes for the fan to then come on on speed 1 as the water in the bottom of the rad gets to about 95 degrees with no air flow from being stationary.

[borarob 0]

just to update this had a play around in my lunch break and have heating back. blower now goes cold and hot as it should. I took the lower part of dash off on the passenger side to check that the slider control for heater control was moving the cable - it was. while I was there I also replaced the missing cog that was stopping my blower directional control working. so at the mo I have working blower, heater and directional control (oh long that will be for who knows!) I also opened up the expansion tank with the engine running and squeezed all pipes and got some air out - which was satisfying. I also noticed that I hadn't put the expansion cap back on properly from the last time I took it off, it was on at an angle and not sitting flush. Did it up correctly and left the engine running - took a nice long while for it to get up to temp and then through to fan cutting in.

 

will see what happens on the way home as no doubt there will be traffic.

 

not all good news though - found my passenger footwell to be damp - now of course given the current situation I would be think heater matrix but all seems well with that. I think it is either leaves in the foliage tray (i park under trees everyday) or that my door skin is not reattached properly (door has recently been off) - I cleaned the car last night so was exposed to lots of water.

 

this corrado lark is fun isn't it!

[colinstubbs 0]

Not all bad though eh? The leak should be an easy fix, good luck 8)

[borarob 0]

no not all bad but seems that way at the moment - have had lots of bad luck with this car over the last month and this today really annoyed me. was sat at work this morning thinking of cutting my losses and getting rid before it costs me any more! then after I had fiddled with it at lunch I went for a little drive which involved going past some glass shop fronts - glimpsed the reflection and remembered how gorgeous the rado is and all thoughts of selling have gone! :D

[colinstubbs 0]

Good keep it that way!!!! Had mine 10 years.... 8)

[borarob 0]

update time.

 

right still have issues with the rado getting hotter than I would like. i've let the engine idle and have established that after about 10-15mins it gets to just above 90 and the fan comes on at speed 1 (fan makes a racket - need a new one). the temp on the gauge goes down a bit at first then continues to rise. it appears that fan speed 2 never comes on as it gets to just below 110 and stays there, no change in fan noise. Does this in traffic - at normal driving it moves between 70 and 90. As previously noted when it gets as hot as about 105 i lose heating in the car, fans just blow cold. i think this is the bypass valve stopping the hot coolant going to the matrix, as it should? or is this something else? is the water pump giving up? how can I easily see if the pump is working?

 

so I think I need, a new radiator fan and motor (i know mine is knackered, bearing has gone and it wobbles alot) and a new fan speed switch. can someone help me out with a part number for this switch (GSF or VAG). also for 1.8 16v it looks like there are only two different types of motor/fan assemblies - one being a 2 pin and the other being 3pin. is that correct? and possibly a new pump....

 

cheers all

[belfastfumanchu 0]

I really think you just need a new bypass valve. If you go to get one though let me know what your dealer says cos Ive had mine on back order for about 3 months. Seems to be some delay in getting them made/shipped or something.

[borarob 0]

really? I do get hot air in the car though, while coolant temp is not too high anyway. and when it does stop blowing hot once the engine has cooled it starts blowing hot air again....

 

my old mk2 golf had a blocked bypass valve and that was just cold air all the time, never got hot. btw when I replaced that my dealer had it on the shelf ( i imagine its the same part?)

[belfastfumanchu 0]

Maybe and maybe not. I think you can have a few different variations of symptons when the bypass valve is on its way out. I know with mine I still got hot air when driving but went cold when i pulled up. Then if I turned the heat off for 5mins and turned it on again I got hot air for a min or so.

For £40 I took a chance and changed it and it solved the problem.

 

Also one other time I had hot air problems it was just the air vent on the near side by the scuttle panel had got clogged up with leaves and I cleaned it up and problem solved.

[borarob 0]

ok, might be worth a go then. I certainly do need to clear out the scuttle tray as it is no doubt full of leaves as I park under a tree everyday.

 

thing is I still think my fan switch is ropey as it doesn't seem to kick in speed 2 just speed 1. so anyone got that part number?

[davidwort 0]

321 959 481 D GSF do them pretty cheaply and they work fine, although the GSF ones (and possibly the new VAG ones) come with a metal washer on them and I prefer the fibre mk2 golf washer you can buy from VW for about a quid. The GSF ones may have very slightly different opening temps stamped on them to the genuine VW part (VW one in my pic) but it's not important as the values are approximate anyway.

 

update:

despite the fact the above part was the original genuine VW one, ETKA actually lists different numbers to this:

 

191 959 481C 95-84 deg C/102-91 deg C 3 pin up to chassis 50-P-020 000

1H0 959 481C 95-84 deg C/102-91 deg C 3 pin from chassis 50-R-000 001 (must be very late cars, 1995? - this is the point at which the wiring connector block changes)

[borarob 0]

so is it just a case of unscrewing old one and screwing in new? is it really necessary to drain coolant or can you do it without - i realise this may be messy! I take it that is the VW part number rather than the GSF?

[colinstubbs 0]

so is it just a case of unscrewing old one and screwing in new? is it really necessary to drain coolant or can you do it without - i realise this may be messy! I take it that is the VW part number rather than the GSF?

 

As long as you're not a complete biff you shouldn't lose much coolant :lol: Just be carefull not to cross-thread the new bugger :wink:

[borarob 0]

well I managed to change the heater matrix bypass valve on my mk2 golf so I should be ok :(

 

i can't find anything called 3pin radiator fan switch on GSF online - are they just referring to it as the thermostat?

[davidwort 0]

we just went to a branch and got them to match the old one from the parts bins, first time they tried to do it via a description they returned with a 2 pin golf switch :roll:

it may not be listed for a 16v engine by GSF, but they definitely stock the right part.

[borarob 0]

ok cheers, think I've sourced one. VW wanted £25 for their part!

 

I think I can def put my issues down to the fan and switch. fan is now no longer coming on at all! fan needs replacing anyway cos bearings are shot so new fan and switch should sort me out I hope. stat is def working cos the bottom rad hose gets hot when it should.

[lesarcsneil 0]

Thanks davidwort, I'd been wondering why my 16v temps had been going up to 110C before the fan started on full speed as it used to stay lower and I hardly ever heard the fan in full speed operation.

 

A quick visit to VW and 321 959 481 D is obsolete, the current part number for a 9A 16v is: 1H0 959 139 B, the price as usual was faintly ridiculous but that's what you go to the dealers for!

 

Cheers,

 

Neil

94 Flash Red 16v

[davidwort 0]

Thanks davidwort, I'd been wondering why my 16v temps had been going up to 110C before the fan started on full speed as it used to stay lower and I hardly ever heard the fan in full speed operation.

 

A quick visit to VW and 321 959 481 D is obsolete, the current part number for a 9A 16v is: 1H0 959 139 B, the price as usual was faintly ridiculous but that's what you go to the dealers for!

 

Cheers,

 

Neil

94 Flash Red 16v

 

the old copy of ETKA I checked actually lists two other numbers, see my updated post on page 1, but it's handy to know the current number VW themselves list.

[lesarcsneil 0]

Wrong, wrong wrong wrong wrong

 

1HO 959 139B is a 4 pin fan switch

 

back to the dealers this lunchtime.... they're only out by one pin.

 

Neil

[borarob 0]

finally got this sorted, swapped out the old and very knackered fan and motor and put a new thermoswitch jobby in. I've got a feeling there's nothing actually wrong with the switch as the motor was very dead - very hard to turn, quite a nice grinding noise.

 

anyone got any tips for testing the switch as if it's ok I'll put it back in as the one I replaced it with has lower temp settings, though I guess there's no real problem with that other than fan coming on a bit more often than it otherwise would?

[davidwort 0]

heat directly over a flame e.g. over a has hob and you'll hear the switch click first setting one then setting two as the temperature rises, use a multimeter or test light to make sure the two circuits complete, dead easy, just don't burn your fingers!