Thread: Please not a head gasket? TD5 D2a

As above - if the top radiator hose gets very hard during warm up then there is a head gasket breach. This overpressure also stops flow through the heater matrix so there will be no ho air from the heater.
Normal coolant pressure in a TD5 is 0.5 -0.7 bar. This pressure allows you to slightly squeeze the top hose. So if the hose is rock hard it means head gasket failure.

So change the overflow bottle cap. If it still presurising then the head comes off


Normally no head work is required. I have done 2 gaskets - my car and a another. In both cases the heads were flat and needed no work.

In both these cases there was no white smoke any time including at start up.

Originally Posted by peter51

Normal coolant pressure in a TD5 is 0.5 -0.7 bar.

Sorry but this is wrong, operating pressure should be 1.4 bar cos that's the tank cap's pressure valve setting as at this temp the boiling point of coolant is increased above 123*C. The gauge stays at the middle up to 120*C so at only 0.7 bar in the system the coolant would start to emit microbubbles at 105*C and boil at 115 and in theyr wisdom they took care at least of that aspect to not have boiling coolant while the gauge is still like normal.

Its not wrong.
Have you actually measured coolant pressure in your TD5 or any other cars or are you just guessing?
You seem so sure of your values so you must have measured the value.
If you have actually measured the pressure in the sytem then please detail your results.

3 of my families Landrovers run coolant pressure guages - 2 TD5's and a P38. my pressure values are correct. These guages are permanently installed because system pressure is so important in cars with cooling systems that are in my opinion undersize.
When I do cooling maintenance, I will pressurised the system using a modified overflow bottle cap and schrader valve, and check for pressure drop over time. It also makes it easy to find leaks on the 24 plus hose clamps on a TD5. Yes all my cooling systems are 100% leakproof so the normal pressure values of 0.5 - 0.7 psi are correct. On a hot QLD day towing up the range then I will see higher but never over 1bar.
I can assure you that any higher than 1.4 bar the hoses are ROCK HARD and the heater in a TD 5 stops working. This I have also measured and observerved using pressure guages. It is not a hypothesis.

I can't contradict your measurements, i didnt measure the pressure, my statement was based on the workshop manual, thermodinamics formula and logic... if you say you measured and that's how it is i apologise but then there's no reason for the 1.4 pressure valve in the tank's cap IMO, and that means it releases the excess to keep 1.4 in the system.... i have temp gauge on the coolant and i've seen between 100 and 110*C towing uphill not once and some times for quite long and according to physics laws at that temp if the pressure was only 0.5-0.7bar the coolant should have started to emit microbubbles which means pressure building up in the system... AFAIK the 1.4 bar is especially calculated so cos there the boiling point of water is 123*C at that pressure .... that's the theory and IMO that's how it should be in a well working system.

Explain please why the pressure valve is at 1.4 bar if the system is supposed to work lower though

Originally Posted by COOLING SYSTEM - TD5- 26-1-6 DESCRIPTION AND OPERATION

...The expansion tank is fitted with a sealed pressure cap. The cap contains a pressure relief valve which opens to allow
excessive pressure and coolant to vent through the overflow pipe. The relief valve is open at a pressure of 1.4 bar (20
lbf.in2) and above....

The pressure is a result of the heat, of course the pressure is lower at normal running temps, vehicle manufacturers obviously have to set the cap releif higher to allow for the odd hot day / towing up a hill etc but not so high as to blow hoses / damage other components, this isn't rocket science, the normal operating pressure is not 1.4 bar on any vehicle and 0.5-0.7 bar sounds right

This discussion might not lead to a widely accepted conclusion cos i'm speaking of an overall calculated pressure of the system and measuring it with a gauge in the top hose or in other thinner hose or thin path in the engine can give different results at the ame time... what i'm convinced of is that when the coolant temp is around 100 the pressure measured below the tank's cap should be very close to 1.4 bar otherwise at 105*C the coolant would start bubbling/boiling... temps between 100 and 110 are not uncommon nor abnormal when towing and above +30 ambient temps are involved that was also admitted/expected by LR that's why they set the electric fan to kick in at 110 to help cooling and the gauge and ECU overheat protection to act at 120*C(i can't say i agree with that just that's how it is)... IMHO it's more important to see the temperature reading near the original sensor than watching the pressure in the cooling system

It is a very good question and low system pressure seems to be intuitively wrong..Only the original engineers would know exactly the correct combination of pressure and flow rate for this specific system.
At 7psi pressure and 50% coolant the boiling point is 120 Celsius ? reference ARE Cooling
The most efficient heat transfer is in the region of nucleate boiling at the metal surface. So they design the pressure and flow to achieve this nucleate boiling ? you would have to talk to the boffins ? but it would be part of the calculation. I accept is as the engineers design point for these vehicles.

The TD5 owner is playing with fire if they don't have good system pressure and at least 50% coolant. Unfortunately it seems some TD5 owners are more interested in fat tyres, suspension mods etc rather than addressing the heart of the engine first. That is why there are so many cooling system issues on this board - 300TDi included Pressure monitoring is essential IMHO.

BTW my cooling systems are factory new so there are no unforeseen pressure losses compared to a newly produced car. All I can say is that this design point is where the TD5 operates on a warm day in QLD (my car 5- 7 psi) and Cairns) my son's car (5-7psi ? Kuranda range 10psi).

I also measure the temperature at the outlet of the thermostat ? it is normally 75 degrees at cruise(78 in traffic). This way I know how effective the thermostat is as the system ages. Saudi Arabian P38s had this monitoring standard as part of OBD. You would get a check engine light if the differential between the upper and lower radiatorhoses was too low.

I also measure the water temperature in the oil cooler of the TD5 ? it can be as high as 107 degrees after just an overtaking manoeuvre of full boost. Normally it is always at 100 degrees there.

I have measured the flow rate from a new TD5 water pump and it is seems intuitively lower than expected? with the engine at 1500 RPM is will only shoot 2 feet out of a ? inch hose.

Maybe you could argue for more flow and more pressure? It could certainly do with a larger radiator but then you are playing with pressure and flows in the system. The water vapour content, temperature and pressure are critical at the inlet to the pump to avoid cavitation.
The pressure is of course not uniform throughout the system because of frictional losses, bends, drops across the radiator etc. etc. However, my measurement is right beside the overflow bottle cap on both TD5's. The P38 measurement(7psi) is in the 8mm hose supplying coolant to heat the throttle plate. The pressures correlate nicely.
The system would have been designed using computational fluid dynamics and it would be designed for the lowest overall weight ? materials plus coolant. I believe it is somewhat undersized. The RRC has a radiator almost twice the volume of a TD5 and can handle all sorts of errant cooling problems including cracked block and head gasket failures to a certain extent. The TD5 and P38 cannot.
When I had my gasket failure in the TD5 you could see the pressure rise incrementally over a short period and then suddenly a week later pressure rising up around 1.4 bar during warmup, rock hard hoses and no heater. So the whole flow regime is changed in the coolant circuit.
Maybe they designed the system to work at a higher pressure and then found out that the heater wouldn't work. Because bean counters run the engineering departments these days and engineers are considered to be in the way of getting products to market, the bean counters would have pushed for a compromise design ? I don't know.
Gotta go because I am fitting Commodore VE V8 electric fans to my RRC this morning and changing all the fluids and fitting a FAST EZI after market ECU
Attached is some interesting data regarding solving chronic overheating in the 2.5TD jeep when it was introduced into SE Asia. Look at how critical flow rate is in a cooling system.
Also the answer may be in this thesis - Modelling and Validation of a Truck Cooling System
Master's thesis performed in Vehicular Systems
at Link?ping University
by
Erik Nordlander

Some of the punctuation symbols screw up when I cut and paste from word, and then post. Hyphens and fractions become question marks.
The size of the hose I mentioned above is 3/4 inch.

Can someone tell me how to avoid this is the future please. I like to compose in word and then cut and paste into the reply.