Coolant problem

Ok Not been on here for a long time So hello again
So u have a problem with my defender td5
Start off with heater going cold when I was in traffic or stopped at red light
So I changed the thermostat and water pump , made no difference so I changed thermostat again as thought could be dodgy also changed the matrix still no different changed rad, all items I replaced were new
Now at 70mph heater hot come to traffic and it gos cold
Also am getting zero pressure in system , top hose soft all the time and only top half of rad getting hot even after a 40 plus mile run
Temp gauge reads normal
Can t understand why no pressure . Can take cap of header tank and nothing not even a hiss
So question is anyone had this prob or anyone have any ideas ?

Header tank cap has a pressure valve this may have failed open. Is it using coolant?

Is your expansion tank cap actually sealing?

Forgot to mention it's a new cap

The discovery TD5 has been known to have a similar issue when the coolant is below the correct level.

Is there any way a cheap crap britpart water pump can let in air ?

Hamsterberg said:

Is there any way a cheap crap britpart water pump can let in air ?

Click to expand...

If it lets air in it will let water out.

Let me get this straight.

Symptoms = Does not hold temperature, system does not pressurise.

Remedies attempted so far =
New cap
New water pump
Flushed the heater matrix
New thermostat (you say it has been replaced twice)

Well that's me flummoxed, I had the same problem with my Pug 206 and a new thermostat solved it instantly.

I'm out but going to watch this fred to see if you fix it.

System holds 22psi for 30 mins in pressure test
When running top hose is soft but hot and heater cold unless doing around 70mph higher the revs hotter the heater gets slow down heater gets cold

So far new rad
New matrix
New water pump
New cap
New thermostat

Oh and with hise in header tank and bleed out no bubbles
Leave hose running and start engine and continues stream of bubbles
Asuming head gasket
Had new head almost 4 years ago

Have you actually tested the thermostat, i.e. in a pan of boiling water? It’s not unusual to get multiple bad ones from new!

Yes I've tested the original one I took out and the two new ones and all open and close

I would guess its the head gasket too.

Had a similar thing happen in a ford ranger
Its leaking combustion gases into the cooling system and displacing the coolant.
The gas pockets get trapped in the heater matrix at low idle and stops heat exchange between the matrix and hot coolant that should be passing through.

Give it the beans on an extended run on the highway, and it would boil away the coolant in time and result in the engine overheating.

I could be wrong though, and I hope I am, so I would suggest you conduct a sniff test to verify if you have combustion gases in the cooling system or not.

Do you know if your head had the plastic locating dowels? If so, were they replaced with metal ones when the head was last done?

The new head came with the metal towels

Update
Fitted another new water pump ( chucking everything at this !! )
Have noticed not only does top hose get hot but no presure but now took outlet hose off matrix and there is no flow at all

A

Hamsterberg said:

Update
Fitted another new water pump ( chucking everything at this !! )
Have noticed not only does top hose get hot but no presure but now took outlet hose off matrix and there is no flow at all

Click to expand...

Air pockets....try bleeding/burping the system properly

Hamsterberg said:

Update
Fitted another new water pump ( chucking everything at this !! )
Have noticed not only does top hose get hot but no presure but now took outlet hose off matrix and there is no flow at all

Click to expand...

Not a Td5 owner myself so not 100% on this but aren't you supposed to raise the header tank during the bleeding process?