HELP!!! engine overheating - at the end of my tether!

hi hope someone can help with this. I've read so much online with so many different ideas and have worked through most and gone round and round in circles!

my 300tdi is overheating. the gauge goes pretty much from stone cold to red in a few miles.
im loosing fluid from the expansion tank cap when it overheats.
radiator is still cold

what i've tried:
Replaced thermostat - no change
compression test through glow plugs - 390psi steady on each cylinder.
pressure test of system - held 15psi for 10mins no drop
drained coolant, removed hoses and checked for blockages, back flushed rad.
refilled with 11.5l water only for now, bled test drove - same issue

I have cold blowers on the heating but on occasions as the temp is rising I have had a blast of warm air.

could someone please help with suggestions on what this could be and why?
in my mind the system is pressurised because of the overheating and that's why im loosing fluid.
I do seem to have lost quite a lot - perhaps this is because its loosing it as steam quicker than I realise?

timbr00 said:

hi hope someone can help with this. I've read so much online with so many different ideas and have worked through most and gone round and round in circles!

my 300tdi is overheating. the gauge goes pretty much from stone cold to red in a few miles.
im loosing fluid from the expansion tank cap when it overheats.
radiator is still cold

what i've tried:
Replaced thermostat - no change
compression test through glow plugs - 390psi steady on each cylinder.
pressure test of system - held 15psi for 10mins no drop
drained coolant, removed hoses and checked for blockages, back flushed rad.
refilled with 11.5l water only for now, bled test drove - same issue

I have cold blowers on the heating but on occasions as the temp is rising I have had a blast of warm air.

could someone please help with suggestions on what this could be and why?
in my mind the system is pressurised because of the overheating and that's why im loosing fluid.
I do seem to have lost quite a lot - perhaps this is because its loosing it as steam quicker than I realise?

Click to expand...

Can't help you mate. You've tapped me out

Water pump?
Did you try with no thermostat?
Blocked radiator?

I wont say the HG as your tests dont really point to it yet, but try the tests you have done with pressuring the system and compression test when its hot (enough to touch)

J

Air lock.

marjon said:

Water pump?
Did you try with no thermostat?
Blocked radiator?

I wont say the HG as your tests dont really point to it yet, but try the tests you have done with pressuring the system and compression test when its hot (enough to touch)

J

Click to expand...

The compression test was done on a warm engine. The pressure test was done without any coolant in. I’d have thought that there would be no change.
Without a thermostat fitted air came out the housing. As I flushed the radiator successfully I discounted a blocked rad.

Stanleysteamer said:

Air lock.

Click to expand...

Possibly but I’ve parked on a decent gradient and ran it trying to expel and air. As it occurred suddenly I was leaning to something failing rather than air as that must have got there somehow.

timbr00 said:

The compression test was done on a warm engine. The pressure test was done without any coolant in. I’d have thought that there would be no change.
Without a thermostat fitted air came out the housing. As I flushed the radiator successfully I discounted a blocked rad.

Click to expand...

I have flushed a rad before and water went in and came out but most of the cooling galeries were blocked. Is it getting warm anywhere?

Waterpump?

J

marjon said:

I have flushed a rad before and water went in and came out but most of the cooling galeries were blocked. Is it getting warm anywhere?

Waterpump?

J

Click to expand...

Not really. Possibly one spot in the middle down one side but only slightly warm.

I don’t see any circulation which makes me think water pump but the p seal failed last year and a new pump fitted by a mechanic then. I did buy a sniff test kit which stayed the same colour for the test but at just over 5mins changed indicating exhaust gases but the test says not to do it for any longer than 5mins due to heat affecting the chemical

timbr00 said:

Possibly but I’ve parked on a decent gradient and ran it trying to expel and air. As it occurred suddenly I was leaning to something failing rather than air as that must have got there somehow.

Click to expand...

These can be tricky to bleed. And there will be a lot of air in the system if you have drained and refilled.
Have you taken the plug off the top of the radiator while filling?

If several attempts at filling fail to restore circulation, try removing the thermostat altogether, it is known that new thermostats don't always work.

timbr00 said:

hi hope someone can help with this. I've read so much online with so many different ideas and have worked through most and gone round and round in circles!
......

Click to expand...

What, if anything, did you do before you had this issue? In other words, did this start happening after a coolant service?

Turboman said:

These can be tricky to bleed. And there will be a lot of air in the system if you have drained and refilled.
Have you taken the plug off the top of the radiator while filling?

If several attempts at filling fail to restore circulation, try removing the thermostat altogether, it known that new thermostats don't always work.

Click to expand...

Thanks. The thing making me think it isn’t air is that I had the fault prior to disturbing anything

SpagettiDefender said:

What, if anything, did you do before you had this issue? In other words, did this start happening after a coolant service?

Click to expand...

I changed the alternator a few days before. Other than that nothing has been disturbed

SpagettiDefender said:

What, if anything, did you do before you had this issue? In other words, did this start happening after a coolant service?

Click to expand...

Post 1.

He says he has drained the coolant, removed all hoses, flushed the rad, and refilled.

Turboman said:

Post 1.

He says he has drained the coolant, removed all hoses, flushed the rad, and refilled.

Click to expand...

Turboman, No this is what I have tried to do to rectify the issue. Yes it’s possible I have airlock now but I have the same issue now as I did before. I didn’t mention in my original post but the 1st thing I did was top up fluids and try to get a flow going. It seems to me that nothing is circulating.

As for radiator not getting hot the pipe from thermostat housing to top of rad is hot

timbr00 said:

Thanks. The thing making me think it isn’t air is that I had the fault prior to disturbing anything

Click to expand...

In that case, try running with the thermostat out, see what happens.

An item that I have found useful with cooling system faults is an infra red temperature pen. They aren't a lot of money, and you can see what is warming up, and how much. A new pressure cap never hurts either.

I dont know the 300tdi circulation system. But no heater leads to circulation issue, if you are getting some warm in the rad leads to circulation issues or blocked rad.


So they are both easier to investigate than a HG

J

marjon said:

I dont know the 300tdi circulation system. But no heater leads to circulation issue, if you are getting some warm in the rad leads to circulation issues or blocked rad.


So they are both easier to investigate than a HG

J

Click to expand...

I like your thinking. Probably because you’re saying it doesn’t sound like HG. I’m going to remove the thermostat as turboman suggested but I wasn’t getting a perfect seal. I guess I can remove the rubber from the thermostat and fit that to seal it up. To my mind the fact the thermostat housing to rad pipe gets hot is saying that it’s opened the stat just not flowing

timbr00 said:

I changed the alternator a few days before. Other than that nothing has been disturbed

Click to expand...

Check the coolant temps upstream and down stream of the water pump with a laser or you can use your hand.

SpagettiDefender said:

Check the coolant temps upstream and down stream of the water pump with a laser or you can use your hand.

Click to expand...

Hot either side

timbr00 said:

Hot either side

Click to expand...

Next step would be to check the temps Rad outflow hose. Also, when it's running set up a camera (or have a friend) monitor the hoses and give the engine some quick throttle inputs. You're looking to see if any of the hoses look like they're sort of collapsing on themselves.

This can be indicative of blockage assuming you don't have any long supplemental coolant lines running to heaters in the back of your Defender.