This is my first experience with any E-type. Reaching out for sage guidance from this esteemed forum:

After an hour driving 60-80 mph noticed temperature gauge dropping, and then it pegged LOW. Checked coolant and it was very low. Topped it off, could see good flow with the cap off radiator. But gage never came back to life. Cleaned sensor connection, with no result. Coolant level remains same after 75 miles more driving. What's the recommended way to check this temperature sensor? Any peculiarities with the Etype that I should know of ?

Engine runs just fine. Exhaust is clean. Oil is clean with no water evidence. No bubbles/ burbling in radiator coolant. Basically no obvious signs of compression leakage into coolant.
Have yet to do cylinder compression test and cooling system pressure test.

 

We always keep a spare sensor, they very cheap and easy to get hold of, I take it the sensor with one wire located on intake manifold?
Just try plugging new one in. If that not works then try checking wiring from gauge to sensor, very simple one wire from.gauge to sensor can check continuity and then you have earth on gauge to the panel and power to gauge, maybe check fuse but that will be ok. Wiring on ours is a bit of a mess as its original, had to replace lots of sections over.the years.
I recently had to re wire ours, I ran completely new wiring to check first and then had the fun trying to route it behind dash and bulkhead and down the frames.

 

Thanks, Will !
I was hoping it would be set up as you said. Easy to check out.
I need to get the gauge working so I can monitor the engine. Oil pressure is perfect, running between 20-40 lbs. Temperature always seemed to be a little cooler (low edge of "normal" range on gauge) than I would expect. Now, I really need that gauge working. Thanks again.

 

we changed to an electric kenlowe fan on ours, i don't know if you are running the same or using a fan powered by belt (original)?
In the UK we run with an old radiator(again probably original) in the middle of the gauge when round town or driving hard maybe a little closer to hot side.
However we recently have had a failure of the temp switch in the header tank which controls the fan switching on, therefore we just keep an eye on it and put the fan on manually. Really i haven't investigated ours to see if it wiring or temp switch but we only use on very short spirited runs or driving to shows.
We are going to be taking ours off the road at somepoint and take the opportunity to rewire the new wiring loom we have for the car. It is a big fiddly job but will sure be worth it.

Anyway back to the thread, i am surprised you are running on the cooler side of things? If you take it for a longer run does it ever get slightly hotter on the gauge?
Still is worth looking at where your failure is in the temp gauge now, maybe a new sensor will make it appear to be running a bit hotter, it is worth a try as said the sensors are very cheap, i think in the £15-£20 range (sorry GBP).
If it still appears to be running cool i would look at the thermostat to make sure it is opening and closing properly. Easy to check when cold it should be closed. There may be a temperature written on it, this is when the stat would open. Best check is to boil some water and then drop the thermostat in the boiling water, it should open. Then pull out water(using pliers as it will be very hot) and it should close. If a stat is not closing properly this can cause the car to run cool as it is not slowing the flow of water down by closing when cool. This means the car will take longer to warm up which may cause increase in fuel consumption as you may need to run the choke longer, but over a long period of time can lead to increased engine wear as the engine is taking longer to get upto correct temp.
Another way to check if the stat is working properly if left in situ is to start the car when cold and feel the top hose it is the larger hose which goes from intake manifold to header tank. I only guessing on time now, but i reckon it probably should take 10mins for this hose to get hot, it should stay cold for 10minutes, then once the car is upto temperature the thermostat will open and allow the flow of hot water into the hose. If the hose is still cool after say 15-20mins or is only slightly getting warm then i bet the thermostat is sticking open.
Sorry if that a little long. Hope it helps

 

Thanks for the detail in your last post.
The full story on this 69 S2 FHC is:
It's a Series 2, so it has the dual fan arrangement, although the RHside fan is seized. The LH fan runs fine and seems adequate running alone. During easy driving (35 mph) the temperature would increase to the lower end of "normal" on the gage, but at higher speeds (40-75 mph) it would drop slightly just below "normal" range.
I assumed this was due to a cooler thermostat being installed, but have not examined it. Regardless, the behavior was consistent anytime I drove the car.
But on a 75 mile trip at speeds averaging 70 mph/ 4000 rpm, it ran in the usual cooler range. However, toward the end of the trip it suddenly began increasing to the higher end of "normal" on the gage. I watched it and kept driving at constant speed (55-60 mph). It remained steady. But when I stopped at a redlight the gage suddenly pegged hard left (below scale markings). It has remained that way since.
Checked coolant level, overfow reservoir was dry, radiator level was extremely low. Oil was almost 1qt low. Topped coolant off with 50/50 mix antifreeze. It took slightly more than a gallon! I freaked !
Also topped off oil with 10W40.
Checked coolant during idle and increased RPM = Coolant dropped slightly at RPM then returned to normal as seen in the radiator fill neck indicating water pump is OK and thermostat was open. Upper and lower radiator hoses remained wide open and showed no sign of collapse at higher flow.
Engine ran fine the entire time, no pinging, no missing or stumbling at idle or at speed, no change in response during acceleration, no popping during deceleration at any RPM.
I've driven it hard several times since my original post (a month ago?) and to date there has been NO loss of coolant, no change in oil color or level.
I was concerned about a leaking head gasket but see no outward signs of such. Still need to run a compression test and cooling system pressure test. Nor have I wrung out the sensor and gage wiring yet. But work has me travelling so much that I haven't had the time.

Any response, additional suggestions/ advice is welcome.

 

Hi Andruet,
Just to ensure we're on the same page, "pegged hard left", would be no reading. That being so, after preforming, as suggested by Will,
1. a Continuance test on the single wire that connects to the Temp Sender
2. a Continuance test on the Temp Gauge fuse to determine its OK

carry out the following test on the gauge.

As this test involves observing the Temp Gauge, for convenience, remove the single wire from the Temp Sender, connect a length of similar gauge electrical wire, of sufficient length to reach into the cabin, to the connector of the wire just removed from the Temp Sender, and take the other end of this wire inside the cabin with you. Whilst observing the Temp gauge, and with the ignition turned on, short the end of the wire directly to Earth. If the Temp gauge is OK, the needle in the gauge will peg straight to the maximum temperature reading of the gauge. If it doesn't move, one of the following faults exist:
1. the gauge is dead
2. the fuse is blown
3. there is no Continuance in the wire to the Temp Sender
4. the gauge is not connected to Earth.

If the gauge doesn't move, check the Fuse, Continuance from the gauge to end of the wire that connects to the Temp Sender, and for connection of the gauge to Earth.


Regards,

Bill

 

Short story:
It was indeed the Temperature Sensor at fault.
Replaced it with a new one, unfortunately it has a "spade" connector instead of the Thumbscrew type. No matter, I just changed it.

Still, many thanks for the detail in all your posts. I had no schematic on hand and was relieved to find the wiring to be as simple as it is.

I'm liking this car more and more as I work on it !