heater blowing out cold air (When it should be hot)

[brizer]

Had this problem a couple of weeks now, I thought it was an air lock at 1st but not sure now.   The temp goes up to 90 still blowing cold air then it drops to 80-85 then it gets hot, then back up to 90 then its cold again & so on. Also If I keep the speed to about 70 it stay hot but if I drop down to about 40 or 50 it go gets cold Again.

           I have heard about the heater blades ?? but not sure what they are & where they are, plus can I do this or is this a job for the garage. One more thing I had to top up with water (about a cup full) the other day & that's a 1st. 

           Any advice will be greatly appreciated, All the best Gerry. 

            

          

[octytdi4x4]

Is the temperature needle going up and down depending on how hard the engine is working? I had this problem several years ago on my bora, it was a 115pd engine, which were allegedly terrible for the head gasket leaking from the cylinder to the waterways somewhere, it never seemed to lose any water, but there was always a little bit of smoke in the header tank, and when it was running there was a constant stream of tiny bubbles coming from the top small hose into the header, it must have been causing an airlock in the cylinder head somewhere and stopping the heat exchanging properly into the water, and I think revving the engine was enough to kind of pump the water around fast enough to get it to blow the airlock clear and send the engine temp back up.

Hope for your sake it's not that, but if it is, use a non oem headgasket to replace it, because as I found, it will probably go again.

[brizer]

Thanks for that but no the needle goes up to 90 with normal driving & is cold then it drops to about 80-85 then it gets hot (sometimes) But I know if I put my foot down it will get hot eventually, then it could stay hot all day then sometimes not. a bit confused . com.

[brizer]

A little update, today I went for a long run on the motorway & my temp gauge warning light came on (low on water) so I left it to cool down while I was at work. the header tank was empty but when I took the cap of a loud hiss telling me it was still under pressure, I wasn't expecting that if I had a water leak & it only took about half a cup of water to bring the levels back up again. Would be great full for any ideas all the best Gerry.

[J306TD]

Let the engine get cold. Undo water cap and idle the engine up to to temp with cap off. Once the fans come on put the heaters onto max heat and fans on full for five mins. Switch engine off. Let cool down and replace cap

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[octytdi4x4]

Pressure in the header doesn't sound good if the engine is clap cold, usually this would indicate gases from the cylinders pressurising the coolant circuit, does sound like a goosed head gasket to me :(

[brizer]

well that's not what I wanted to hear looks like a trip to the garage then, but before I do that I will try the other idea 1st when I get home tonight (clutching at straws here) but who knows. Failing that does any one know how much it will cost for a head gasket as its done 170.000 miles but only a 55 plate is it worth having done. ????

Thank you both for your advice all the best Gerry.

[octytdi4x4]

A good garage should be able to confirm whether or not it's the case anyway mate, they can do a test in the water circuit for exhaust gases.

[brizer]

Looks like that's the way to go then, so thank you all for your help & hope to let you know the outcome when I get the chance to take it in. will be away at the end of the month so will try then need the car right now, will keep some water in the boot just in case.

      All the best Gerry