Engine coolant temperature sensor

Does anybody know how critical it is that the P38 Diesel runs at a constant temperature?
The only reason I ask is that mine seems to run smack bang in the middle of the temperature gauge when its under load, going up long hills etc etc but when its going down hill or just cruising the temp falls to just above the blue.
It's been like it for ages and hasn't really bothered me until the other day when I thought it felt like it was periodically struggling slightly for power.
I happened to be having a read up on Rave this evening about the above sensor and it mentions that it use the information from this sensor to adjust the timing??
I'm not sure where the temperature gauge was reading when the feeling of power loss happened but I just wondered if I'm barking up the wrong tree?
To throw another problem in the mix the vehicles running a kenlowe fan. The dial for the kenlowe is adjusted for normal driving conditions.

Any suggestions gents greatly received,


Dave

You are barking up the wrong tree. Engine coolant temp sensor measures just that engine coolant temp. It has nothing to do with timing or any other function other than driving the gauge on the dash. However the ECU coolant temp sensor does effect the fuelling, timing and glow plug operation. When it detects the engine cold the signal from it tells the ECU to retard injection, sets rich fuel for start and fast tickover, lets the glow plugs function. When the engine reaches a certain temperature the ECU switches off the cold start functions according to the signal from the temp sensor..

Sounds like a duff or missing thermostat to me.

Datatek said:

Sounds like a duff or missing thermostat to me.

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Yep that's about it Keith, more likely to be missing, waxstats always fail shut and cause overheat.

Thanks guys. I will order up a thermostat before I investigate. If there's one in there it wont hurt to replace it.
Just out of interest, why would somebody take a thermostat out and not replace it? (Or don't I want to know)
Would it be worth replacing the water pump at the same time? I'm not sure when it was last replaced and from what I have read they give little if no prior warning before they give up.

Dave

buy a genuine thermostat a britpart one cost me an engine! cooked the head and cracked it!
if there is no stat in it usually removed for overheating or poss head gasket issues, but in your case as the guage does not go above half way when working hard you may have been lucky and it has failed open.
if it had any serious issues with headgasket etc even with the stat removed it would still prob overheat when working hard up a hill ie towing some weight

Davlyn said:

Thanks guys. I will order up a thermostat before I investigate. If there's one in there it wont hurt to replace it.
Just out of interest, why would somebody take a thermostat out and not replace it? (Or don't I want to know)
Would it be worth replacing the water pump at the same time? I'm not sure when it was last replaced and from what I have read they give little if no prior warning before they give up.

Dave

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Deffo replace the water pump while you are at it if it has a plastic impeller. Get a metal one.
If the stat is missing it's likely to be due to overheating. This is often caused by a faulty viscous fan of a silted up RAD, so ensure you flush the rad off the car and upside down because as both hoses go in the top there is nothing to stop the bottom of the rad filling up with sludge

6704nathan said:

buy a genuine thermostat a britpart one cost me an engine! cooked the head and cracked it!
if there is no stat in it usually removed for overheating or poss head gasket issues, but in your case as the guage does not go above half way when working hard you may have been lucky and it has failed open.
if it had any serious issues with headgasket etc even with the stat removed it would still prob overheat when working hard up a hill ie towing some weight

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As i said before waxstats NEVER fail open. If they lose their wax pellet which is the only reason they fail. They cannot fail open. Unless the spring has failed. I have never ever seen one with failed spring.

wammers said:

As i said before waxstats NEVER fail open. If they lose their wax pellet which is the only reason they fail. They cannot fail open. Unless the spring has failed. I have never ever seen one with failed spring.

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Hang on Tony, he said it cooked his engine, so by implication it must have failed closed exactly as you correctly state He did go on to contradict himself when I read it again, and say it might of failed open but you have nailed that many times.

Datatek said:

Hang on Tony, he said it cooked his engine, so by implication it must have failed closed exactly as you correctly state He did go on to contradict himself when I read it again, and say it might of failed open but you have nailed that many times.

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Waxstats were a bloody menace when they first appeared they always failed shut and caused over heating. They have now been modified to overcome that to some degree. They still always fail shut BUT they have a bypass valve built in. They now have two valves, one that is shut, the main one, and a plate on the end. There is now always water flow through the rad, not a lot, but enough to stop the engine cooking if the stat fails. In the cold state water flows through a bypass gallery until the main valve opens to give full flow, as the main valve opens the plate on the end covers the bypass gallery. It is held there by spring pressure which still allows the main valve to cycle to control flow. If the main valve fails the bypass is perminently open.

wammers said:

As i said before waxstats NEVER fail open. If they lose their wax pellet which is the only reason they fail. They cannot fail open. Unless the spring has failed. I have never ever seen one with failed spring.

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Sorry for being a div, but are waxstats another make of thermostat?

Iv'e used britpart thermos and only one out of three worked with the kettle test.

Mike.

The genuine Land Rover stat has BMW stamped on it.

THE BUDDAH said:

Sorry for being a div, but are waxstats another make of thermostat?

Iv'e used britpart thermos and only one out of three worked with the kettle test.

Mike.

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+

Waxstat is not a make but a type, wax is the medium used to open the stat

THE BUDDAH said:

Sorry for being a div, but are waxstats another make of thermostat?

Iv'e used britpart thermos and only one out of three worked with the kettle test.

Mike.

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No waxstats are called that because of the nature of how they work. The old bellows type stats were filled with spirit, when they failed they always failed open. Waxstat work on a different principal. If you look at one they are held closed by a spring. The small pushrod goes down into the casing that contains a wax pellet. When the wax gets hot it expands forcing the pushrod to open the stat. The only real way they fail is if the seal goes over time and they lose the wax. Having lost the wax they cannot open. That is why most modern engines are fitted with the bypass seal type as described earlier it gives some protection against breakdown if the engine is run light until the stat is replaced. In this day and age with all the crap parts coming from China and elswhere it is a good policy to warm even new stats to make sure they work.

I have a P38 R reg and when i turn the engine on the gauge moves a mm and does not move any more. Is it a chance i don't have a theromstat in there? and thus need to change it?

gcracingteam said:

I have a P38 R reg and when i turn the engine on the gauge moves a mm and does not move any more. Is it a chance i don't have a theromstat in there? and thus need to change it?

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Thus. Or maybe not thus.

gcracingteam said:

I have a P38 R reg and when i turn the engine on the gauge moves a mm and does not move any more. Is it a chance i don't have a theromstat in there? and thus need to change it?

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:welcome2:

If it is a petrol model, the stat is in a plastic housing plumbed into the system, so it would be difficult not to have one....

The diesel is more conventionally placed in the engine block, so could be missing....

If you gauge doesn't move when driving and the engine is warm.....

Petrol - Dodgy Temp Sender
Diesel - Dodgy Temp Sender or Missing stat....

Don't forget to put a little more detail into your posts, with engine size, type etc, also a location helps incase some one is close by who can help out.....

Saint.V8 said:

:welcome2:

If it is a petrol model, the stat is in a plastic housing plumbed into the system, so it would be difficult not to have one....

The diesel is more conventionally placed in the engine block, so could be missing....

If you gauge doesn't move when driving and the engine is warm.....

Petrol - Dodgy Temp Sender
Diesel - Dodgy Temp Sender or Missing stat....

Don't forget to put a little more detail into your posts, with engine size, type etc, also a location helps incase some one is close by who can help out.....

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As per the usual, Saint made what I was trying to say much easier to grok.

Mine does exactly the same - gauge sits just above the blue unless worked whereupon it goes to about 12 o'clock and stays there. Even towing a couple of tonnes yesterday it didn't go above 12 o'clock. The other interesting thing is with aircon on, it always sits at around 12 o'clock.

Would be interested to hear if you do get to the bottom of this. I know some others on here have reported exactly the same behaviour with their P38 diesels, so I am hoping it is nothing to worry about........!

I also noticed during the very cold weather we had a few months back that the heater starts warming the cabin pretty quickly after cold start, surely if the thermostat was missing (I've never checked this) it would take ages to warm up?


Cheers,

Jerry

jerrytlr said:

Mine does exactly the same - gauge sits just above the blue unless worked whereupon it goes to about 12 o'clock and stays there. Even towing a couple of tonnes yesterday it didn't go above 12 o'clock. The other interesting thing is with aircon on, it always sits at around 12 o'clock.

Would be interested to hear if you do get to the bottom of this. I know some others on here have reported exactly the same behaviour with their P38 diesels, so I am hoping it is nothing to worry about........!

I also noticed during the very cold weather we had a few months back that the heater starts warming the cabin pretty quickly after cold start, surely if the thermostat was missing (I've never checked this) it would take ages to warm up?


Cheers,

Jerry

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I'd bet your stat is missing or stuck, water at 30C in the heater will feel warm on a cold day but it will still be a cold engine