Thread: Coolant level senders Tdi

Originally Posted by Mikems

Could anyone suggest the best type of sender for a coolant level alarm. ie float in the reservoir or sensor in the top radiator hose. I was under the understanding that you could run out of coolant but still have some in the reservoir. As with a normal non pressureized reservoir system. Looking at the system on the D1 Tdi there is a hose from the bottom of the reservoir to the bottom of the radiator. This changes things a bit so a sensor in the reservoir would be OK. Is this right.

I think that the sensor in the radiator (top hose fitting) would be the best bet. No moving parts, float switches can stick. Plus it alerts you as soon as the level drops in the radiator - where it's important, several factors could stop the level dropping in the tank, heat, position of leak etc.,

That's only my view - I am sure others will have theirs.

Mine is "taped" in to the plug on the top of the radiator so if the level in the radiator starts to drop it goes off

Originally Posted by Mikems

Could anyone suggest the best type of sender for a coolant level alarm. ie float in the reservoir or sensor in the top radiator hose. I was under the understanding that you could run out of coolant but still have some in the reservoir. As with a normal non pressureized reservoir system. Looking at the system on the D1 Tdi there is a hose from the bottom of the reservoir to the bottom of the radiator. This changes things a bit so a sensor in the reservoir would be OK. Is this right.

Yes this is correct. On a Tdi the best 2 places to fit a coolant level sensor are the radiator or the header tank. It is impossible for the level in the header tank to vary from the level in the radiator (unlike the old non-pressurised overflow tanks) because there are two hoses connecting the tank to the cooling system. The bottom hose going to the bottom radiator hose and the top hose going to the top of the radiator mean that the tank will always equalise with the radiator level. The only possible and very unlikely cause of this being different is if either of those hoses are completely blocked.

The worst place to fit a coolant level sensor is in the thermostat housing. When the engine is running this is the last place to reflect low coolant level.

Paul

I have had the Engine Saver ( sponsor of this site I believe ) fitted in the top radiator hose for six months or so now - works a treat. The only thing is the self test "beeeeeeeep" on start up seems to be getting a bit longer - I know there's plenty of coolant there maybe the sensor needs a clean ?

I just have a range rover expansion tank cap . They have the senser built into the cap . Just wire it up to a alarm and job done

Thanks for your input. Its good to have someone to bounce these things off. I'm still not sure how to cover all the contingentcies. Maybe 2 censors may be the answer. I appears to me having the water pump inlet just a few mm lower than the top radiator hose, you would not have to loose much coolant before the pump ran dry. This may be why head gaskets & cracking is such a problem with these motors. I may look at putting a sensor box in the air purge line in the top of the radiator. I am assuming the non return valve allows air to go from the radiator to the expansion tank.
Thanks again for your idears.
Michael.

he only thing is the self test "beeeeeeeep" on start up seems to be getting a bit longer - I know there's plenty of coolant there maybe the sensor needs a clean ?

Wayne, I contacted David re this as I was also concerned. It was his opinion that there is still air trapped in the system from the installation. I have had a few goes at this & the test beep is much shorter now.

Even when it was beeping longer, it soon cleared.

On the V8i D1 the hose is the highest point in the system & so air can gather there.
I made up a 'tool' to help bleed this without wasting coolant. Mail me if you would like further details, although it was posted on here some time back.

"Even when it was beeping longer, it soon cleared."

Does this mean it stops beeping even though there is still air in the system.
How much air is needed in the system to set it off when the engine is running. The Tdi pump is mounted higher than most engines & for this reason you wouldn't need to loose too much coolant before you started doing damage. I would be interested to hear at what stage these alarms go off at.
Michael.