O Bife
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What would be the symptoms one a 2.5 DSE if the thermostat was on the blink?
Thermostat on the blink?
- Thread starter O Bife
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Musicmaker
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I think my thermostat is fecked as well. The temp gauge on my P38 DSE hardly goes past the blue. A way to test is to take the thermostat out to see if it has closed fully then bung it a pot of boiling water to see if it opens fully. Not done mine yet of course 
O Bife
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In my case it is over heating! Could it still be the thermostat?
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Yes most definitely, waxstats very rarely if ever fail open.
O Bife
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Can I remove the thermostat without replacing it? (Everywhere is closed now until Friday)
By that I mean will I be able to refit the pipe to the block without a thermostat in place, or does the thermostat need to be in place for the joining/fitting of the pipe to the block?
By that I mean will I be able to refit the pipe to the block without a thermostat in place, or does the thermostat need to be in place for the joining/fitting of the pipe to the block?
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- 58,170
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- Preston Lancs.
I think my thermostat is fecked as well. The temp gauge on my P38 DSE hardly goes past the blue. A way to test is to take the thermostat out to see if it has closed fully then bung it a pot of boiling water to see if it opens fully. Not done mine yet of course
Check if you have one in at all. Waxstats very rarely if ever fail open unless the return spring has failed, if it hasn't they always fail shut.
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Yes it can be removed without a problem..
O Bife
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And I can put it back together without a thermostat in place?
Mine did fail open
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Then the spring must have failed or the piston snagged. Natural position for a stat is shut. This is done by spring pressure. The only way it can open is if the wax is heated and expands that is how they work. If the wax is lost (usual fail) then they cannot open.
Datatek
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Yep, it's a common dodge on diesels with a suspect cooling system.
gibby_wls
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I don't know if its the same on the Diesel as the Petrol but check the breather pipe from the top of the rad to the overflow is flowing, quick check showed to me by mechanic is it will be hot at both ends if its flowing, if not that could be blocked airlocking the rad, quicker than taking the stat off and having to replace all the coolant.
O Bife
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On mine last night the hose coming from the block to the rad was hissing at it's join to the block, but it was not at all hot in it's middle and all the way from there to the rad itself. Also it was "soft" or easy to squeeze, no pressure at all.
On the other end, by that I mean the plastic top-up tank, as I released it slightly, it started bubbling away and water (HOT) started pouring out of the overflow pipe.
Also, there was no hot air coming into the cab although I had the heater set at 25ºC.
not sure what caused the failure with mine, either it was stuck around half open or spring failure causing it to open way to soon,
confident radiator outlet didn't get hot at startup when other pipes did.
anyway the odd behavior made me and I admit stupidly change out temp sensor before stat
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A thermostat stuck shut should not stop flow through heater. You maybe need to check for flow maybe the water pump has given up the ghost. Was rad hot all over top and bottom?
Datatek
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O Bife
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The water pump is ok.
As for a stuck thermo stuck shut not stopping the cab heating, doesn't the cab heating system work off the warm/hot water from the engine?
If so, if there is no flow (due to the knackered thermo), wont that mean no cab heater?
As for the rad, cool on top. I didn't check the bottom. As I said before, the hose coming from the block to the rad (just under the ERG) was just warmish to the touch and it didn't have any pressure. When I say just warm I mean it was luke warm compared to the top up tank which I couldn't touch for long due to it being RUDDY hot.
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Thermostat has a bypass valve built in, before stat opens flow is from front of head through bypass to heater and back to rear of head. So block and head warm first. Then when thermostat opens bypass is closed and coolant goes through radiator via main gallery. So heater should warm long before rad does. Sounds like thermostat is stuck shut but why heater is cool is a mystery..
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I've had two fail 'by' over cooling one on a P38 and one on a 90; didn't work out why they failed but opening far more than they should at a give temperature was the problem, fixed by a new 'stat in both cases (with the same temp spec)
