Initial start pre heater warming

Post by **AngeloEvs** » 25 Jul 2008, 17:59

The Haynes maunual is very unclear about the following, can someone clarify:-

1 The second thermostat coolant sensor and its function. Haynes only refers to this in connection with the 2.1 injected engine.

2. The 'thermo switch' in the Pierburg body. Haynes manual depicts this as providing a 12V feed to a relay (X-contact load reduction???) which controls the following heater elements to improve cold start and economy:

a) Inlet manifold b) Choke left c) Throttle Channel

The 'thermo switch' should switch off all heating elements at 60 degrees.

Q1. What is the function of the second coolant sensor on a 1.9DG?

Q2 What exactly are b and c and what do they do?

Q3 If the heating elements remain on due to a faulty thermo switch I would imagine that 'Hot starting' (engine up to temp) would be difficult.

Q4 If running on LPG then wouldn't the above be a disadvantage given that LPG is better with cold air and prefers part rather than full choke?

Post by **Mocki** » 25 Jul 2008, 18:16

Q1. What is the function of the second coolant sensor on a 1.9DG?
It sends the temp signal to the relay, which controls the heaters

Q2 What exactly are b and c and what do they do?
They would be what they say on the tin, so to speak, as shown in the diagram, im guessing

Q3 If the heating elements remain on due to a faulty thermo switch I would imagine that 'Hot starting' (engine up to temp) would be difficult.
Im not sure there would be much effect to starting, other than the battery not getting as much charge........when its warm, it warmer than the heater makes it, or the heater wouldnt turn off when working correctly

Q4 If running on LPG then is this level of preheating necessary?
YES i lent someone my relay, and so didnt have any heating, and forgot about it, come winter i found it made a difference

Post by **AngeloEvs** » 25 Jul 2008, 18:28

Thats the trouble with the Haynes manual, it shows the components in the circuit diagram, details the inlet manifold heater and nothing about the 'choke left' and 'throttle channel' heaters. So if the coolant sender in the thermostat housing controls the relay what does the 'thermo switch' in the carb do?

Post by **Mocki** » 25 Jul 2008, 18:33

it , iirc , operates tells the choke and the pull down what the temp is at the carb, as oposed to the temp at the engine

Post by **AngeloEvs** » 25 Jul 2008, 18:41

So difficulty in starting a hot engine could be attributed to these components. I disconnected the second coolant sender and drove home to replace the O ring, etc. stopped the engine momentarily and found it diificult to restart. Never had this prob before and wondered if it was associated with the sender circuit and what it did exactly. Many thanks Mocki.

Post by **Mocki** » 25 Jul 2008, 18:45

no, i think it happens the other way round, tbh, if its not connected it dont heat , not it constantly heats, but i may be wrong on that.......

Post by **AngeloEvs** » 25 Jul 2008, 19:13

You are more than likely correct Mocki, that would be the sensible way of controlling the pre-heaters, may be just a coincidence not starting first time. The Carb Thermo switch is definitely depicted in the manual as switching 'off' at 60 degrees. Will investigate further after I have bled the cooling system.

Post by **AngeloEvs** » 25 Jul 2008, 19:58

Is there a better manual than the Haynes? The carb chapter shows the thermo switch connected to the ICU and bears no resemblance to the circuit diagram which shows it controlling a relay.

Post by **R0B** » 25 Jul 2008, 20:04

the bentley manual is a lot better.for most things.but alas does not cover carbs.they dont use them in the states.apparently...

Is there a better manual than the Haynes?

Post by **AngeloEvs** » 25 Jul 2008, 20:45

Thanks Rob, me thinks the T25 carb/fuel system could do with a book of its own let alone a chapter but will get the Bentley. Oh for the days when all you had was a simple pull knob for the choke and a pedal to open the throttle!

Post by **AngeloEvs** » 26 Jul 2008, 19:52

Thermo switch on carb body connects choke element to ground, after warm up, thermo switch open circuit and disconnects choke element, secondary coolant sensor controls inlet heater and throttle according to the measurements I took today.