Hi folks,

 

New member from New Zealand here looking for some advice to try and fix my polo.

 

Firstly, I would just like to say thank you to all the kind people that take the time to offer technical support and advise on this forum. I have used it may times over the last few years with my Polo and especially over the last week or so (there are a number of good posts here with the same / similar issues to what I am experiencing at the moment).

 

I have a 1997 Mk3 6N Auto.

 

I’ll start by summarising the problem in two bullets then give the full background below 😊

 

-   Radiator cooling fans not working

-   Cabin heater only blowing cold air

 

So, the background is as follows. last weekend I replaced the water pump, test drove the car which seemed fine, returned home and let car idle while I monitored for any leaks etc. Noticed temp gauge creep past the 90-degree mark. Revved it for a bit and temp continued to climb.

 

First thing I observed was the radiator fans were not running. Now to be fair, they may not have been running before I did the coolant pump. This being my wife’s car, I’m not driving it daily so the problem may have been there for some time. I have definitely heard the fans running in the past so know they have been operational before.

 

My initial assumption was Air lock after replacing the pump. So, the following tests / actions have been performed:

 

-   Re-drained, filled and bled the cooling system (no change)

-   Tested and visually checked all relevant fuses (all working)

-   Jumped Thermo switch and confirmed fan working on both high and low.

-   Replaced Thermo switch with new unit (no change)

 

At this stage I felt up (sorry about that) the lower radiator hose and noticed that it was hot at the top part of the hose but cold at the bottom part of the hose…

 

-   Pulled out and tested thermostat (found it would open but not close)

-   Replaced thermostat with new unit (no change)

 

Wondered if somehow not enough coolant was getting into the radiator and therefore not triggering thermo switch.

 

Wondered if I didn’t install Thermostat correctly.

 

Read on this forum that the Thermostat housing can break where the pin connects and therefor thermostat does not function properly.

 

-  Removed thermostat, checked housing and found to be fine, reconnected pipes, bled cooling system and ran it without the thermostat installed (no change).

 

Coolant seems to be getting into the radiator fine as I have drained it about 4 times now.

 

So, I am out of ideas and I would love any thoughts or advice you may have that could help me troubleshoot this problem.

 

Thanks in advance!

Matt from NZ

Edited 28 September, 20196 yr by MattFromNZ

Welcome to the Forum.

 

As far as your radiator fan is concerned, it may well be (hopefully) that you don't even have a problem!

The engine should normally run at about 90°C WITHOUT the fan running - you normally have to go well above 90 before the fan will cut in.

As the system is pressurised, the pressure being created by the coolant expanding in the sealed system, the coolant will not boil until it is well over 100°C. The actual pressure is regulated by a valve in the filler cap, but any leaks in the system would cause the coolant to boil at 100.

As the thermostat would not close, this could account for the heater not becoming hot, so it might pay (with the new thermostat in position) to check if the heater is now working. If not, and seeing that you have well and truly cleaned out the system, I would suggest that the heater fault could be due to one of the following.

(1) Air in the heater circuit.

(2) Heater matrix still blocked.

(3) The inside of one of the heater hoses has partially collapsed and is blocking the coolant flow.

(4) The heater control valve is faulty.

 

With the thermostat working correctly, you should be able to feel the main hoses, which should remain fairly cool until the thermostat opens, at which point, the 'top' hoe will become very hot and the 'bottom' hose may even become cooler as cold coolant from the radiator flows to the engine.

 

Do let us know of your findings.

 

Regards

Hi Caretakerplus,

 

Thank you for your reply, your help is much appreciated!

 

So for the radiator fan issue, unfortunately the temperature does climb up well past the 110 degree mark to the point that the dash warning light comes on, which is where I shut it down.

 

I am just considering your point about a leak in the system. If I have a leak, causing the coolant to boil, I would expect that the fans would be triggered to turn on regardless?

 

The issue with the heater not blowing hot is not a big problem for me but I assumed it was related to the radiator fan issue which is why I mention it.

 

So, yesterday I re-installed the thermostat (making sure that I had it all lined up correctly) and tonight after work I will run the car and check to see if the heater is still blowing cold and I will re-check the radiator hoses to see if they are showing signs that the thermostat is working.

 

I will update you on the results! J

 

Thanks again,

Matt

Are you sure the pump is actually circulating the coolant? (they only really work above 2k rpm ) as the symptoms sound like your not getting the flow past the fan switch to signal that, coupled with the no cabin heater just make me think of no coolant being pumped around.

 

As this is more engine related I've moved it to the engine section.

Hello Nige8021,

 

Thanks for your reply.

 

I’m glad you suggested that as that’s been in the back of my mind given the problem appears to have started after replacing the pump.

 

The replacement pump was new but it was a cheaper off brand product. It is possible that it has malfunctioned I suppose. I didn’t notice any problem with it when inspecting it before installing it but to be honest all I really did was spin it by hand to make sure smooth bearing operation.

 

I wondered if I could have installed it incorrectly but can’t imagine how giving it only seems to bolt on one way and if it wasn’t seated correctly id know about it.

 

So, I am now considering pulling it out and inspecting it again.. but that will have to wait till next weekend 🙂

 

Cheers,

Matt

Edited 29 September, 20196 yr by MattFromNZ
Typo

Before you rip the pump out, try this method:-  Cold engine, remove expansion bottle cap, top up to MAX line, leave cap off, start engine, select full Hot on the heater and hold RPM  @ 1500~2000 until the temp gauge reads 90c, then hold the RPM at 2000 for at least 5 mins, stop engine and top up if required, refit expansion bottle cap and restart and hold at 2000 for at least 10 mins, switch off then allow to cool and adjust level if required 

Thank you again, i will try this and let you know how it goes!

 

Cheers,

Matt

 

Hello,

 

Quick update.

 

I followed Nige’s method and here’s what happened:

 

Filled expansion bottle to MAX, cap off, heater on full hot, revved to about 2k RPM until it got to the 90deg mark, then continued to hold RPM.

 

Within about a minute or less from when I got to the 90deg mark, coolant was surging and overflowing the expansion tank, quite a lot of it. It got to the point where I had about 200ml on the garage floor.

 

At this stage I loosely put the cap back on the expansion bottle, just to try and reduce the spill..

 

Then after about 3-4 minutes the temp gauge had past the 110 degree mark and the dash warning light came on.

 

I turned off the engine, and about 5 seconds later.. the fan came on!

 

So I fired up the engine again to see if the fan would bring the temperature down.. it didn’t really and I wasn’t too keen to risk my head gasket so I turned it off again.

 

Some observations:

- interestingly the fan did not continue to run after I turned off the car the second time

- when the fan was running, it was on low speed (I think).

- the cabin fan did not heat up at all during this process

- the lower radiator hose was warm at the bottom (previously it stayed cold)

 

So, my current hypothesis is that an air lock was the culprit, and not enough coolant in the system to trigger the thermo switch (until now).

 

My plan of attack is to wait until the engine is cold (tomorrow), top up the coolant and repeat Nige’s instructions (maybe this time with the cap on???). Hopefully this will continue to bleed any air out of the system and get some coolant through it.

 

I will let you know how it goes.

 

Cheers

Matt

Edited 30 September, 20196 yr by MattFromNZ
format

5 hours ago, MattFromNZ said:

Filled expansion bottle to MAX, cap off,

 

Hope you meant to the MAX line, as I said and not to the brim of the expansion bottle ?

Yes, sorry I meant MAX line 😊.

 

 

Hello,

 

Quick update:

 

I topped up the coolant to the MAX line and it took more than what was lost yesterday which I am hoping means that it has taken more into the radiator.

 

I ran the car per the method but no change really. i.e. it ran up to past 110 deg, dash warning came on and i shut it down. No radiator fan running this time.

 

I will check again tomorrow on the coolant level.

 

Cheers,

Matt

 

Hi folks,

 

Just to update and close this out for those who may find this post helpful in the future.

 

I didn’t see any improvement after trying to bleed the cooling system of air so in the end I pulled the pump out and found that the plastic impeller was broken. It had sheared off the shaft completely. Replaced the pump with a good quality German made unit and the car is now running better than ever.

 

Thanks Nige8021 and Caretakerplus for your help, it was much appreciated!

 

Cheers,

Matt

Glad that you are sorted out'

 

I was going to mention 'beware of plastic impellers', but thought that they were long gone.

 

Regards