How to change the temp probe and thermostat.

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How to change the temp probe and thermostat.

Post by FalcoColumbarius »

This is posted by Big Bird. The original thread:

How to change the temp probe and thermostat.
Postby Big-Bird » 07 Mar 2015, 13:44

The 4M40 has great access to most of the engine bay components. If you ever wondered how to work on some common parts for the cooling I got you covered!


Thermostats and Temperature Probes are very important to the 4M40 because when they misbehave they affect fuel economy, glow plug life expectancy(and how the GP system functions). A bad temp probe sends a bogus signal to the computer and prevents the glow plug system from functioning at top efficiency. The Thermostat is stuck open or the rubber seals have gotten hard (age) the coolant will continuously circulate through the rad and in winter the engine won't reach proper operating temps. Fuel won't atomize properly, it certainly won't burn fully and your Delica will have crap fuel economy.

How to fix these???Actually its very easy and best done when the engine is cold.

Remove the intercooler unit and set it aside. Drain and capture the coolant at the butterfly valve located on lower rad tank (drivers side). The valve should be turned 1 to 1.5 turns, any more than that and the plug pops out and coolant sprays everywhere. Also remove the rad cap and the Air-Plug(in my hand) located beside the fresh air intake vent for your heater/AC system


Next remove the 2 bolts that hold the thermostat housing. There is no need to loosen the rad-hose clamp as the housing and hose can be moved aside easily. There will be a mess soon so get the catch basin positioned for the next part!


Once the cover is off you will see the nose of the thermostat sticking out. It will need some gentle prying with a screwdriver to get it's the messy part folks.


Install the new thermostat with the springs in first. The thermostat doesn't care what clock-position its in but I do prefer to have nose laying horizontally. Next bolt up the if all you needed is a new thermostat then button everything back up including the intercooler.....DON'T install the Air Plug yet!!!!!

Add coolant until nearly everything you drained is poured back in. Next start the engine and watch for fluid to start rising out the air-bleed hose...just before it starts to dribble out install the air-plug and gently tighten.....its only plastic. Add coolant to top off system and you're done. Wash the engine off as coolant can ruin belts and it stinks when it bakes off a hot engine.

The all important tempurature probe sends a signal to the gauge in your instrument cluster and its also monitored by the Glow-Plug system.

The probe is located next to where the upper radiator hose attaches to the intake manifold.


The probe has 2 contacts and the power connection does have a release clip.
Once the connection has been removed you will need a deep 14mm socket to remove the old plug and to install the new one(the deep socket prevents damage to the spade connections)


Add teflon tape only to the threads on the new sensor and reinstall. Plug it in.
Top up coolant after you install the intercooler....the air bleed plug should be removed to let trapped air exit the system. Your're done!!! Simple.

This is some of the stuff I'll cover on our Calgary Delica Tech Night........we should do a webcast for! Who has web-savy and will be attending the tech night????

We might be doing ball joints and brakes that night! Fun stuff!

Thank you Big Bird!

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