Discovery II TD5 coolant pressurised

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sierrafery said:
For those fitted withPDC0000 70(Defender/D2 Td5, 4.0 V8, RR P38 2.5 DSE) the description is the same, only about prerssure relief valve at 140KPa(20psi) as stamped on the cap albeit on some sites it's listed as used for L322 too and the description for that it's differento_O
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Cap vents at standard cooling systems pressure of 15 PSI. Vents any overfill. 140 Kpa is the burst pressure to prevent system damage. It's PCD000070 by the way. ;)
 
AFAIK 140 is set so cos at that pressure the boiling point of coolant is raised above 120*C as to not boil while the gauge is still at the middle as it stays there up to 120... i'm not gonna contradict you on this cos i didnt measure the pressure myself but 15psi(103.4KPa) for a cooling system seems low to me cos in some places can be below the ambient pressure and the normal boiling point of water(100*C) is reached at 14.7psi.... so with cold stationary engine the pessure in the system can be the same with the ambient pressure and that can't stay there when the coolant gets hot as PV/T should stay constant so if the temp rises the pressure should rise too as the volume of the system is constant...though if you measured a hot engine's coolant pressure with a gauge(provided it has a well working and tightened cap) and you got 15psi i will not argue with that cos i'm not 100% convinced like in the other "hot" subject:).... i have an old cap which i replaced cos it was suspect so i might fit a gauge to it and measure the air pressure in tank just cos you made me curious cos for me a system which has 15psi can hardly be called "pressurised" :cool:
 
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sierrafery said:
Maybe on other vehicles... the D2's tank cap has only one pressure release valve which should open at 1.4 bar. The sniff test on diesels can be irrelevant in some cases
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Hi sierrafery My existing tank cap has a spring and I cant see any pressure valves. The replacement cap (bought on eBay yesterday) does have two valves showing and no spring. It is listed for D1D2 as well as Defender and range rover.
The sniff test can be irrelevant? Can you provide some cases? I'm getting worried now. Thanks
 
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I think it depends on which kind of leak detection tool was used, mine passed a test like this but as it still pressurised the top hose i bit the bullet and got the head removed and pressure tested then it became obvious that it had a small crack in it which allowed gasses into the cooling system and also read similar reports on the web in other cases too... though i'm not a specialist in this area so wait for confirmation just that it happened to me so i shared my own experience
 
sierrafery said:
I think it depends on which kind of leak detection tool was used, mine passed a test like this but as it still pressurised the top hose i bit the bullet and got the head removed and pressure tested then it became obvious that it had a small crack in it which allowed gasses into the cooling system and also read similar reports on the web in other cases too... though i'm not a specialist in this area so wait for confirmation just that it happened to me so i shared my own experience
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Right thanks
 
sierrafery said:
AFAIK 140 is set so cos at that pressure the boiling point of coolant is raised above 120*C as to not boil while the gauge is still at the middle as it stays there up to 120... i'm not gonna contradict you on this cos i didnt measure the pressure myself but 15psi(103.4KPa) for a cooling system seems low to me cos in some places can be below the ambient pressure and the normal boiling point of water(100*C) is reached at 14.7psi.... so with cold stationary engine the pessure in the system can be the same with the ambient pressure and that can't stay there when the coolant gets hot as PV/T should stay constant so if the temp rises the pressure should rise too as the volume of the system is constant...though if you measured a hot engine's coolant pressure with a gauge(provided it has a well working and tightened cap) and you got 15psi i will not argue with that cos i'm not 100% convinced like in the other "hot" subject:).... i have an old cap which i replaced cos it was suspect so i might fit a gauge to it and measure the air pressure in tank just cos you made me curious cos for me a system which has 15psi can hardly be called "pressurised" :cool:
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Are you being serious? Any pressure generated by heat in the cooling system is positive pressure above atmospheric. For every 1 pound PSI over and above atmospheric pressure the boiling point of water is raised 3 degrees F. So with a 15 PSI cap the boiling point would rise from 212 degrees F at standard atmosphere to 257 degrees F at 15 PSI above standard atmosphere. The cooling system, depending on the thermostat fitted, will normally run at somewhere around mid point of available cap pressure. It will vent at 15 PSI and let go altogether at around 20-22 PSI to prevent system damage. The system does not run at 20 PSI. I have cooling system static pressure and cap testing equipment.
 
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sierrafery said:
That's a kind of answer i like even if it proves me i was wrong... so no comment on that, thanks for clarifying :cool:
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When cap is in tester it should hold pressure until 15 PSI then start to vent. Static test rig can be used to either pressurise system cold to check for leaks or be fitted to unpressurised system and engine run to check for undue pressure buildup as it heats. A normal engine will run at 5 to 7 PSI at idle with gauge showing normal mid range depending on stat. Minimalistic test units can be got for fifty quid, comprehensive universal units like the one i have can cost several hundred pounds.
 
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wammers said:
When cap is in tester it should hold pressure until 15 PSI then start to vent. Static test rig can be used to either pressurise system cold to check for leaks or be fitted to unpressurised system and engine run to check for undue pressure buildup as it heats. A normal engine will run at 5 to 7 PSI at idle with gauge showing normal mid range depending on stat. Minimalistic test units can be got for fifty quid, comprehensive universal units like the one i have can cost several hundred pounds.
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I've learned something usefull... i'll remember that
 
Update. I have fitted the new cap and carried out a sniff test. The sniff test passed. Driving locally within a range of less than 10 miles each way the car is OK. There is little loss of coolant. However going off to Swindon last night a distance from me of 34 miles it overheated at about 33 miles. I managed to get to Swindon. I opened the bonnet and found that the coolant had been vented from the expansion tank -it was all of the engine compartment. So the new cap is working. Later I topped up the coolant and went back home via the A3102, avoiding the motorway. Driving at 40-50 miles an hour, with the heater set to 28C had the heater water sloshing around on the journey but noted that the coolant top hose was not pressurised when I got home. No coolant in it?

Could the heater trapped air lead to the engine overheating, by causing an air lock, and with the generated high pressure was venting the coolant?

This morning I topped up the coolant and put in about 6 litres!
 
Hi Neilly When I top up the expansion tank I raise it using a plank of wood so it is higher than the top hose. When I bleed the top hose I do not have the expansion tank elevated. Is that wrong? I am parking the car facing up hill so the bleed valve is higher.
 
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Although if you managed to get 6 litres in the system, after driving it, then something does not sound good.

Cheers
 
neilly said:
Hi @geoff edwards

One thing does spring to my mind from the distant past.

Have a look here,
https://www.aulro.com/afvb/discovery-2-a/212384-thermostat-fitted-reverse.html

May be worth checking it is correct.

@Alan Crossley , not sure if they are the same or not, but might be worth you checking yours as well, knowing how you have cooling issues.

Cheers
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neilly said:
How had you been bleeding the system then?

Cheers
Click to expand...
Topping the expansion container up in the raised position then bleeding the system. Also parking the car with the bonnet uphill and before next use bleeding the system.
 
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