Thread: Best Tdi 300 Overheat Alarm

There is a fourth option.

A low coolant alarm.

It probably would have been the ideal system to warn of your split hose.

https://davesitshop.com/emporium/ind...&product_id=48

Hi Will

all three of your options would be best. However I run an exhaust temp gauge (pyrometer) and a temp alarm unit with digital display. The sensor is bolted to one of the bolts on the thermostat housing.

For me that is enough security. I can see if there is too much un burnt fuel coming out the exhaust from pyro gauge and if the cooling system is running hotter than normal from the temp alarm display.

Cheers
Michael.

Originally Posted by Pacemaker

Hi Will

all three of your options would be best. However I run an exhaust temp gauge (pyrometer) and a temp alarm unit with digital display. The sensor is bolted to one of the bolts on the thermostat housing.

For me that is enough security. I can see if there is too much un burnt fuel coming out the exhaust from pyro gauge and if the cooling system is running hotter than normal from the temp alarm display.

Cheers
Michael.

Curious....why there and not directly onto the Head ??

Welcome to the forum, Will.

I made and fit a low-coolant alarm (followed an article on an MG forum) and am in the process of fitting a pyrometer to measure exhaust temps as I want to enrich (I guess you'd call it) my diesel injection at the DIP. Too high exhaust gas temps can burn valves and IIRC destroy the turbo.

Overheating usually arises from coolant system issues, although these can also be coupled with low engine oil or incorrect timing, both of which will exacerbate those problems. So I am of the view that a low-coolant alarm or more accurate temp gauge than the LR standard should be the first step in engine temp management.

Yesterday, I fitted one of those digital temperature gauges mentioned in this thread.
http://www.aulro.com/afvb/discovery-...ml#post2226015

Robmacca, I can't speak for Pacemaker, but my decision to locate the sensor where I did was based on three factors.

1. It was the only bolt I could find on the head that was a convenient size.
2. It was accessible and in a slightly protected location.
3. Most importantly it was on a lump of alloy very close to the place where the coolant left the head and entered the top of the radiator. I figured that would be where the water was hottest and that the heat would transfer quickly through the alloy and my homemade copper sensor holder.

I believe it is doing its job there because I have been quite impressed with how quickly things change from the temperature going up to the temperature going down. Just a few seconds after cresting a hill, the temperature begins to drop, so the heat transfer must be quite efficient.

On my 300Tdi, the wire from the ignition switch to the fuel solenoid on the injector pump goes via a temperature sensitive switch on the cylinder head. This opens at 105 degrees C. which is above desirable operating temperature but before heat induced damage occurs. So motor stops whatever the cause. Have a push button bypass which can be held down so motor can be run if overheat switch opens. Most likely only for a very short time eg to drive off the road.


If the switch opens for some reason such as very hot day / pulling heavy load and cooling system needing cleanout, water temperature could drop to normal very quickly when load removed. However, it may take some time for head to cool enough for temp switch to close again. As temp sensitive switch just has spade terminals , wire to it from ignition switch can just be put straight onto fuel solenoid. Just need to remember that there is no overheat protection.


If this circuit also includes an oil pressure switch, which can be adjusted to only close above eg 10 psi (the opposite of how normal oil light switches operate), it is necessary to hold the override button down when starting until oil pressure builds up (and/or have a time delay switch .) Have not yet got around to installing one of these on my LR but have them on motors of tractors and other agricultural machines.


It is important to note that this type of protection is largely fail safe. ie motor will not run if protection device malfunctions. With some types of protection devices, if they malfunction, will not stop motor or provide warning. Also, I remember seeing more than one report on aulro of ignorant drivers - invariably not the owner who just keep going . Ignoring the warning alarm and cooking a motor. Usual excuse something like "I was just trying to get home".

Thanks Gents

Sounds like the simplest and most important option is an alarm about the water, either Dave's option where the sensor is inline or one that simply uses a bolt on the housing.

Definitely need an audible alarm, it is too easy to miss a glowing light while driving.

I am approaching retirement so the low mileage Tdi will become my primary vehicle with the old girl becoming the backup. I have just had delivered galvanized tub cappings and some fibreglass doors should arrive in the next few days.

Best Wishes

Will

Originally Posted by mox

On my 300Tdi, the wire from the ignition switch to the fuel solenoid on the injector pump goes via a temperature sensitive switch on the cylinder head. This opens at 105 degrees C. which is above desirable operating temperature but before heat induced damage occurs. So motor stops whatever the cause. Have a push button bypass which can be held down so motor can be run if overheat switch opens. Most likely only for a very short time eg to drive off the road.


If the switch opens for some reason such as very hot day / pulling heavy load and cooling system needing cleanout, water temperature could drop to normal very quickly when load removed. However, it may take some time for head to cool enough for temp switch to close again. As temp sensitive switch just has spade terminals , wire to it from ignition switch can just be put straight onto fuel solenoid. Just need to remember that there is no overheat protection.


If this circuit also includes an oil pressure switch, which can be adjusted to only close above eg 10 psi (the opposite of how normal oil light switches operate), it is necessary to hold the override button down when starting until oil pressure builds up (and/or have a time delay switch .) Have not yet got around to installing one of these on my LR but have them on motors of tractors and other agricultural machines.


It is important to note that this type of protection is largely fail safe. ie motor will not run if protection device malfunctions. With some types of protection devices, if they malfunction, will not stop motor or provide warning. Also, I remember seeing more than one report on aulro of ignorant drivers - invariably not the owner who just keep going . Ignoring the warning alarm and cooking a motor. Usual excuse something like "I was just trying to get home".

Hmm, there is no way on earth I'd set my engine up like that.
Too great a risk of putting yourself in a precarious position on the open road with the engine cutting out at just the wrong moment.

FWIW 105° is well within operating limits of a Tdi, I've seen it multiple times with an accurate mechanical temp gauge, if you want to use some sort of alarm, set it past 115°.
IIIRC the high temp fan switch on a Disco switches at close to that temp.