overheating, or is it?

Can anyone shed any light on whats caused this.

Bit of a run down but after hearing a dry rumbling noise and finding water underneath the front passenger side we renewed the water pump. That was last week, since then it's been used twice for about 10 miles. Every so often the heater stops working running cold and the temp needle goes off the scale.
After going around a corner the needle comes back down and the heater comes back.
Just driven from Grimsby to Boston and nearly at Boston the needles goes off the scale, heaters stop working. Got out, popped the bonnet, water pipes are solid, released the pressure on the header tank and everything is ok for about a mile. Needle all over the place.
Stopped the car, no pressure, turned key to position 1, temp needle sits half way, start car and it rises to the top again, stop car and put key to position 1, needle sits half way.
Engine doesn't feel overly warm.

Already had someone tell me it's probably a cracked head, but i'd prefer to explore any easier, cheaper options before stripping the engine to pieces again.

cheaper suggestions.. huge airlock from fitting the pump?

you can stick an analyser or crystals over the tank to see if it's the head.

is the rad hot all over or is it blocked?

hopefully someone smarter will be along

well, ran it to temp, took it on a 3 mile drive and the temp gauge is up in the red again.

does rad get hot all overt core surface , head gasket is a very common cause more so than heads cracking though it does happen

Did you put a cheep crappy water pump in?

Does it have a pipe from the rad back to the header tank? If so blow it through with an air line in case it is blocked and is stopping the air from bleeding back to the header tank.

just driven it 16 miles, needle was up to the top a lot of the time, cold heaters, and the rest of the time, it was sitting in the middle and I had lovely warm heaters. Gauge is all over the shop.
After the drive, engine felt normal to the touch...

jamesmartin said:

does rad get hot all overt core surface , head gasket is a very common cause more so than heads cracking though it does happen

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can't get to the radiator at the minute, have winch in the way lol. Will investigate further when/if i get it home tomorrow.

warrior said:

Did you put a cheep crappy water pump in?

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Was a bearmach one.

clivesP38 said:

Does it have a pipe from the rad back to the header tank? If so blow it through with an air line in case it is blocked and is stopping the air from bleeding back to the header tank.

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god knows lol, again, will have a proper look in daylight.

you can from the inside thats were id check anyhow

Sounds like a mofo airlock to me

went from my sisters to the indian take away 3 miles away, needle off the scale before i'd even left the drive...

M0YAA said:

went from my sisters to the indian take away 3 miles away, needle off the scale before i'd even left the drive...

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you should of ordered the korma not the phall simples

cold heater + temp rising and heaters ok temp normal sounds like air in there somwhere causing an airlock every now and again.
heater matrix is the highest point, try bleeding it all again and see what happens.

could always drive up a hill so the exp is highest and se if it helps to clear it

I would say air lock, take top hose off heater and run until no air comes out then put back on. Get some help to put a few revs on and to top up as you go.

did you fill/bleed it from the thermo housing?

THEengineer said:

did you fill/bleed it from the thermo housing?

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yup, took in excess of 4 litres of water through the screw

M0YAA said:

yup, took in excess of 4 litres of water through the screw

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Bit late on, but I'm having exactly same issue... you sort it?