Hi. I have -86 Polo 86 Classic. 1.3 bensin engine code MH. Problem is heater wont blow hot air into cabin.

 

I have changed these parts:

-thermostat (with new gasket)

-flush the whole system

-water pump

-radiator

-heater matrix.

 

Engine is heating, but it wont reach 90 degrees on speedo meter. Radiator temp sensor is working, because liquids in the motor froze last winter, which made the engine heat up and speedometer was alerting that.. Did i blow head gasket with this trick? Or what else should i be checking before taking the motor apart.

 

 

 

E: Formatting

 

 

 

 

Edited 29 November, 20241 yr by poolo86c

Just checking do know the side vents deliver fresh not heated air.

 

Did you open the small valve on top of the new heater matrix when filling to remove all air bubbles?

 

Is the heater matrix housing fitted tight to the bulkhead? If not you get cold air around it entering.

 

Does the heater fan turn?

Usually when the resistor pack fails it will only spin on 3 the fastest setting.

 

Does the top pipe to radiator get hot?

One of the two pipes to heater matrix?

 

Edited 7 December, 20241 yr by dvderlm

On 07/12/2024 at 13:00, dvderlm said:

Just checking do know the side vents deliver fresh not heated air.

-> Yes, this is clear to me.

 

Did you open the small valve on top of the new heater matrix when filling to remove all air bubbles?

-> Yes, this is done and no air in the system.

 

Is the heater matrix housing fitted tight to the bulkhead? If not you get cold air around it entering.

-> Yep, with new rubber gasket around it and little bit sealing compound on top of it.

 

Does the heater fan turn?

Usually when the resistor pack fails it will only spin on 3 the fastest setting.

-> Yes, on every volume.

 

Does the top pipe to radiator get hot?

One of the two pipes to heater matrix?

-> No.

 

I removed thermostat from the engine and "thermostat cover" was oval shaped and little bit crooked, so I think this could be the main issue for problems with engine temps. Ill keep this post updated till problem is solved.

 

If thermostat not closing the hot water will prefer to go towards inlet manifold and radiator than heater matrix.

 

Good luck.

On 10/12/2024 at 18:32, dvderlm said:

If thermostat not closing the hot water will prefer to go towards inlet manifold and radiator than heater matrix.

 

Good luck.

This seems to be the problem. Engine temps rose a bit, but not to 90°C. Could it be that brand new thermostat(??) was already broken, which seems odd, but I guess anything is possible.

Where bought from?

Had it been dropped?

 

Maybe the whole cooling system could do with draining and reverse flushing.

I've come across waxy yellow stuff in pipes at the carb autochoke, which I assume was some previous owner using leak fix additive. 

 

You could test new thermostat by adding boiling water to cold water in a bowl jug in which it hangs with a thermometer. Don't go over 95°.

 

Is the thermostat specified to open at ~90°C (I think 87 and 92 degrees are common) and is not a hot countries 80°C type?

 

I have also seen a "turbo"thermostat rated 74°C though for stupid money.

 

Edited 14 December, 20241 yr by dvderlm

But distorted thermostat cover sounds obvious suspect.

4 hours ago, dvderlm said:

Where bought from? From local dealership, cost around 10€

Had it been dropped? Not that I remember

 

Maybe the whole cooling system could do with draining and reverse flushing.

I've come across waxy yellow stuff in pipes at the carb autochoke, which I assume was some previous owner using leak fix additive. 

 

You could test new thermostat by adding boiling water to cold water in a bowl jug in which it hangs with a thermometer. Don't go over 95°.

 

Is the thermostat specified to open at ~90°C (I think 87 and 92 degrees are common) and is not a hot countries 80°C type?

 

I have also seen a "turbo"thermostat rated 74°C though for stupid money.

 

I did a test run with car, with new termostat cover and no leaks, so thats good. I drove about 30km and engine temps around 30-40°C according to the speedometer..

 

I ordered brand new thermostat which will arrive next tuesday, I'll check back after I have changed that. Im going to boil the new thermostat, in order to see if that works.

Edited 14 December, 20241 yr by poolo86c

You could get an Infrared thermometer and point it at the block and hoses, radiator top and bottom.

 

From memory I see hot to touch hoses around 70°C and exhaust pipe temps of nearly 300°C.

 

If coolant is being lost via headgasket you would see white smoke steam from exhaust and lower temps until too little coolant.

 

You can get a block tester kit which detects CO2 in the coolant

eg

https://www.ebay.co.uk/itm/387555287404

Few days later and Im back losing my mind over this car. Good news, new thermostat works. I boiled it and it shut and opened as it should. It helped the temperature thing, temps came up a little bit after running the engine for 20min, but not to 90°C. Also it kept flashing the red coolant light on dashboard. No visible leaks from the outside, so I guess its leaking inwards due broken headgasket, as I thought and feared from the beginning.

 

Also new problem. Heater wont start. I bought new heater relay and checked the fuses, nothing. Must have been some kind of electrical problem, which I have to dig into after changing the head gasket.

So flashing red light because coolant level dropped enough to trigger the level sensor on the reservoir.

 

shame, but you at least replaced cheapest, easiest things first.