Overheating / cold blower problem

[kickboxer]

For the last 10 months of owning my Terrano the temp gauge has never moved past half way (normaly just a fraction below).
Last night while stuck in the M6 traffic jam I noticed that the heater had gone cold, when looking at the temp gauge I noticed it was at the 3/4 mark and rising. I managed to pull over just before it hit the red and allowed it to cool down. Checked the water levels and all appeared fine, fan was also working fine.
Started off again and same thing was happening, it would stay at normal temp and then rise but then would fall back again thought it maybe due to the traffic stop start but then it started to do it with a clear road.
But the strange thing is when the temp is normal the heater blows hot air but when the temp is at 3/4 the the heater only blows cold air.

Any suggestions what may be going on here?

I had a new heater matrix in April so dont think it could be that.

 

[Lazy-Ferret]

That sounds like you have air in the system... they can be a real pig to bleed properly...

I still have not found a good way to do it, and tend to just keep squeezing the top radiator pipe with the engine running, and the rad cap off, until it stops letting bubbles through....

You have to keep topping it up as you un-squeeze the pipe and need to make sure the engine is up to temp, and the thermostat is open, I think that was what I did wrong the other week, when I had all the problems, as I fitted a hotter stat, and did not wait long enough for it to open.

Also make sure the header tank is full up to the max mark.

Once you haven't got any more bubbles coming through, top the rad up, and fit the rad cap. Then, squeeze the top pipe again, to force the air in the overflow pipe through to the header tank. Then hopefully, as it cools down, it will suck water, not air back into the system.

Good Luck...

 

[kickboxer]

If it is air should I be concerned about how the air is getting into the system ?

 

[glanrichbex]

Leaking Head gasket?

 

[(RIP) PLANK]

TTT2 has experience of the 3.0 engine, he might have some advice :thumb2

 

[kickboxer]

What i dont understand is why it cycles between hot and normal and why the heater blows cold when the engine is hot.
If it was a theromstat of gasket problem surely it would just stay hot ?

 

[Barrbeast]

+ 1 for air.

When it's at normal the air bubble/whatever isn't around the engine or in the heater matrix (possibly in the radiator at that point?).

When it's hot the air is around the engine and in the heater matrix so a) the engine starts to overheat as there's no water to cool it down and b) the heater blows cold as there's no water to heat up the air.

If you've got air in the system then I would guess you've got a leak from somewhere and should be losing water, what are the levels like?

For bleeding I don't know whether it'd work for a Terrano but when I replaced the water pump on my old Shogun (was leaking as soon as the engine stopped) the way I bled the system was to put the front wheels on the ramps so the radiator cap was near as damn it the highest point in the system then started the engine, took the radiator cap off and left it running. Once all the bubbles were stopped I topped up the levels, left it for 5 mins and put the cap back on. :thumb2

 

[Banshee]

+ 1 for air.

When it's at normal the air bubble/whatever isn't around the engine or in the heater matrix (possibly in the radiator at that point?).

When it's hot the air is around the engine and in the heater matrix so a) the engine starts to overheat as there's no water to cool it down and b) the heater blows cold as there's no water to heat up the air.

If you've got air in the system then I would guess you've got a leak from somewhere and should be losing water, what are the levels like?

For bleeding I don't know whether it'd work for a Terrano but when I replaced the water pump on my old Shogun (was leaking as soon as the engine stopped) the way I bled the system was to put the front wheels on the ramps so the radiator cap was near as damn it the highest point in the system then started the engine, took the radiator cap off and left it running. Once all the bubbles were stopped I topped up the levels, left it for 5 mins and put the cap back on. :thumb2

2+!!!!

Mine was the same when I hadn't bled it correctly when I did the water pump

 

[Lazy-Ferret]

If it is air should I be concerned about how the air is getting into the system ?

When the water is hot, it expands in volume, lifting the rad cap a bit, and allows the excess water to flow into the header tank. As it cools, the vacuum created by the water contracting back to it's cold volume, should cause the water to be drawn back past the rad cap from the expansion tank, to re-fill the system.

Do you have enough water in the header tank?

I would be looking at the pipe that runs from the top of the radiator to the expansion tank, there were no pipe clips on mine, and over the years the pipe had hardened, and was not sealing, so it was easier to draw air in through he pipe join, than lift the water from the header tank.

It could also be the radiator cap not sealing, so instead of drawing water from the header, it draws air past the seal... it could also be any other pipe which is not done up tight enough...

It may just still be in there from when you had the heater matrix done.

Of course, it could be all the bad things as well, like problems with the turbo, cylinder head gasket, etc.

 

[kickboxer]

Thanks guys I will give it a good bleeding over the weekend and hope that solves the problem. If it the head gasket then it will be going as I cannot plough anymore money into it, which would be a shame as I have had some great fun in it.

 

[Banshee]

Thanks guys I will give it a good bleeding over the weekend and hope that solves the problem. If it the head gasket then it will be going as I cannot plough anymore money into it, which would be a shame as I have had some great fun in it.

Me and the Mrs are going to be near Cambridge one of the weekends soon, if you need a hand diagnosing it mate, I'd more than happily help you out

Any luck with the discs?

 

[kickboxer]

Me and the Mrs are going to be near Cambridge one of the weekends soon, if you need a hand diagnosing it mate, I'd more than happily help you out

Any luck with the discs?

Thanks for offer but I had a look after work today, got very worried when it took 4 litres to top up the rad, but then discovered wet carpet so pretty sure it's the heater matrix, need to go to the garage on Monday and have a word as it was only changed in April.
Discs have not arrived yet, will give it another day then p.m. you.

 

[Sweety]

I had to do the water pump on my last one twice in a month I just toped the system up, left the rad cap off, started it up & ran the heater at full speed onto the screen & it bled no probs at all. Ten took it for a 5 mile run let it cool down & topped up the rad a touch & never had any probs