Erratic Heater Behaviour

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harri46
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Erratic Heater Behaviour

Post by harri46 » 15/02/20 15:37

Hi All

The heater on my mk2 is very erratic. Generally goes from warm (it never gets hot) to virtually cold air. I have noticed recently, that I can switch the blower fan on once the car's warmed up and it blows warm air for maybe 20 or 30 seconds then it ends up blowing almost cold air.

The temperature gauge is generally normal, there is no leaks in the system. I have been thinking about getting the heater matrix reverse flushed, but surely if that was blocked I wouldn't get any warm air at all?

I have been looking online and apparently the heater control valve can cause erratic heater behaviour, just wondered if anyone else has experienced similar problems.

Be grateful for any info and advice.

Kind regards

Darren



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peteV6R5
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Re: Erratic Heater Behaviour

Post by peteV6R5 » 15/02/20 16:20

you got air in the system, need to bleed it all out.
couple of items in KY2 to help.

https://www.mr2oc.co.uk/know-your-2/mk2 ... bartid=149
https://www.mr2oc.co.uk/know-your-2/mk2 ... bartid=161

bleed valve for heater is in the frunk behind the spare wheel, top of the heater valve.
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harri46
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Re: Erratic Heater Behaviour

Post by harri46 » 16/02/20 10:45

Thanks for the reply.

I don't think there is air in the system. I used to have a gurgling sound in the dash but haven't had that since I had a new radiator fitted. When I have been trying fix the heater problem, I have also run the engine with filler cap off just to make sure there wasn't air in the system.

I am mystified what the problem can be.

Darren

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Re: Erratic Heater Behaviour

Post by peteV6R5 » 16/02/20 12:37

harri46 wrote: ↑
16/02/20 10:45
Thanks for the reply.

I don't think there is air in the system. I used to have a gurgling sound in the dash but haven't had that since I had a new radiator fitted. When I have been trying fix the heater problem, I have also run the engine with filler cap off just to make sure there wasn't air in the system.

I am mystified what the problem can be.

Darren
new Rad..... not bled properly, can tell you you have air in the system. simples
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Re: Erratic Heater Behaviour

Post by jimi » 16/02/20 16:40

You need to follow the proper bleeding procedure, running the engine with the cap off will not eliminate all the air.
Click the second link that Pete posted and follow (exactly) the procedure in the article starting at part 25.
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harri46
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Re: Erratic Heater Behaviour

Post by harri46 » 28/02/20 23:33

Thanks for all the replies.

Booked the car in now to have the heater matrix/core reverse flushed and to have the cooling system bled.

Hopefully, fingers crossed, that will finally cure the problem.

Darren

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Re: Erratic Heater Behaviour

Post by jimi » 29/02/20 13:48

I hope the garage you are using are familiar with the MR2 cooling system and its idiosyncrasies, especially when it comes to bleeding. It's not like other cars ;)
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Re: Erratic Heater Behaviour

Post by harri46 » 29/02/20 19:13

Hopefully, I am going to request that he bleeds the heater and radiator bleed valves. Should have done it when he fitted the radiator but he obviously didn't. Also just realised that the coolant overflow tank is empty, dont know if this will have had any affect on any air in the cooling system.

Darren

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Re: Erratic Heater Behaviour

Post by jimi » 29/02/20 20:12

Yes it will, it needs to have a level above the bottom line otherwise when the system cools down it will draw air into the system.
I'd seriously suggest he follows the proper procedure as detailed in the link previously posted, otherwise it's pretty unlikely all the air will eliminated from the system
Click the second link that Pete posted and follow (exactly) the procedure in the article starting at part 25.
https://www.mr2oc.co.uk/know-your-2/mk2 ... bartid=161
Black is not a colour ! .... Its the absence of colour
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