andyfreelandy

andyfreelandy

Well-Known Member
Some clarification please.

My FBH runs at 5 degrees or below which is correct.
When the car is fully warmed up and outside temperature still below 5 degrees it still runs.

Reading RAVE, the internal FBH ECU should detect the coolant temperature and then control the FBH as required.

Do I have a fault, can the ECU be interrogated ?
If this is working as designed then I feel a modification coming on !!
 
Rave suggests that there is a sensor in the heat exchanger that is used to measure coolant temperature - see extract:

The heat exchanger transfers heat generated by combustion to the coolant. A
sensor in the heat exchanger provides the ECU with an input of heat exchanger casing temperature, which the ECU
relates to coolant temperature and uses to control system operation. The temperature settings in the ECU are
calibrated to compensate for the difference between coolant temperature and the heat exchanger casing temperature
detected by the sensor. Typically, as the coolant temperature increases, the coolant will be approximately 7 °C (12.6
°F) hotter than the temperature detected by the sensor; as the coolant temperature decreases, the coolant will be
approximately 2 °C (3.6 °F) cooler than the temperature detected by the sensor.
Rave suggests that there is a sensor in the heat exchanger that is used to measure coolant temperature.

So - either the sensor is not working or the coolant temperature doesn't make the required figure??

No diagrams show this sensor - only the front bumper outdoor temp one.

Investigation will continue with a temperature check of a fully warmed up car where the FBH still operates.
 
Don't know how relevant it is but the fbh on my l322 cuts on and off when the engine is up to temp.
I've assumed it's to keep at operating temp while idling, keeping emissions low (assume fbh emissions don't count)
 
I'd run the live data for the engine, to make sure it's getting up above 80°C. IIRC the FBH ECM will try to maintain a temperature of 75°C, so the heater will be more effective. Once the coolant is above 75°C, the FBH should shutdown, or at least stop burning fuel. If the coolant doesn't go above the FBH control temperature, then the FBH will run when it's not needed.
 
Possibly. I am surprised that the stat has much part to play when engine fully warmed, but looks like it does. Temp gauge does go up and down at the moment so a working stat works hard on a TD4.
 
Hi Andy.
Don't know if this video will help but i will post the link anyways, i do know a chap whom used to refurbish all FBH units if you ever need his number.

 
Thanks. FBH is working fine. Looking at the temp gauge with FBH off, the thermostat in engine has failed open. Never passes 1/4 way.
 
andyfreelandy said:
Thanks. FBH is working fine. Looking at the temp gauge with FBH off, the thermostat in engine has failed open. Never passes 1/4 way.
Click to expand...
That's what they do. 2 options available. Either fit an in line thermostat, which is pretty easy, or replace the thermostat, which is a ball ache, hence most people take the easy route.
 
andyfreelandy said:
Thanks. FBH is working fine. Looking at the temp gauge with FBH off, the thermostat in engine has failed open. Never passes 1/4 way.
Click to expand...
Hi Andy.
John as mentioned the inline stat, which is fairly easy to implement, I think the Auto TD4 is a bit more awkward.
manual you just need to file or cut through the original stainless steel band.
wEM9j8xl.jpg
1

A lot easier if the manifold is removed but can be done without.
lw3AU5Ml.jpg
2

NylsWXyl.jpg
3

This hose was removed from the FL1 to insert the inline stat, the hose at the top is from a Rover 75 which we also fit the inline stat.
W9KYiytl.jpg
4

2YRrwMNl.jpg
5

4J9Mc9ul.jpg
6

I like to use gates stats
YABgztJl.jpg
7

azfzSvZl.jpg
8

PdH8JXFl.jpg
9

nPhw9qOl.jpg
10

I use an alloy tube to push the stat further into the hose, plastic sink pipe will do the same job.
UXvKTWhl.jpg
11
 
Many thanks. Wondered which way around it went!

Am assuming once the original has failed it won't start working again or won't close permanently.
 
andyfreelandy said:
Many thanks. Wondered which way around it went!

Am assuming once the original has failed it won't start working again or won't close permanently.
Click to expand...
Had the in-line mod in my TD4 for 2 years or so now - no problems at all.
(And nice and warm in winter).

FBH works fine still 😁

Free tip - silicone grease is your only friend with this one!
 
Last edited:
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andyfreelandy said:
Many thanks. Wondered which way around it went!

Am assuming once the original has failed it won't start working again or won't close permanently.
Click to expand...
No problem if it starts working again and I imagine once broke it'll just stay open. Not heard of one going closed.
 
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