4.2 cooling mystery

[H7OB]

I wonder if anyone could help me with a bit of an anomally (to me!)

After an engine rebuild Ive been very conscious of engine temperatures. Friday AM it drove perfectly in the hot weather. Friday PM the electric fan didnt come on and the temperature rose quickly but didnt overheat. We bypassed the relay and hot wired it to get the short distance home. The following day I went to try it again but despite the fan on it quickly got hot when driving, rather than the opposite.

Today it has had the relay changed and an over-ride switch wired in. We adjusted the thermostat on the hose and got the car to sit stationary at a steady 88° ish on the gauge. The strange thing is that now the temeprature rises really quickly once the car is on the move. The fan seems to be drawing the air through the rad as before. My concern was the fan might be fighting the external airflow but it had never done this previously. The temperature gun shows the water to be circulating at approx 10° cooler than the gauge reads. Mine seems to be the only E that runs cooler when stationary!

The only additional thing is that I previously fitted C27650 thermostat as its a 68 S1.5. On closer scrutiny it would seem I need C3731/1 as it has the bypass slit so Ill aim to fit that once shes cool enough.

Any inputs gratefully recieved!

[H7OB]

Progress update...
Yesterday I managed to change the thermostat to C3731/1 and the car seems to run just the same. Stays steady at tickover at about 88 on the gauge. When driving it climbs right back up again.

On closer inspection I found some premature wear on the inside of the belt.


My only thought is that could the belt be slipping once more power / revs are being put through it. It has a new spring tensioner so I’ll see if I can add a bit more tension by adjusting the alternator. I’ve ordered a new belt as well as a temperature sensor, but that seems fine at tickover. Will update once I’ve changed the belt.
All good fun!

[abowie]

Can't shed much light on your problem but there was a batch of crap fanbelts recently from the usuals in the UK which split and delaminated very quickly.

[Geoff Green]

Which way is the fan moving air through the radiator? Needs to flow from front of car to rear?

[christopher storey]

As Geoff has said, you need to check that the fan is sucking not blowing ( assuming it's mounted behind the radiator ) . A sheet of newspaper, or even a tissue, will soon tell you . Your symptoms sound to me suspiciously like the fan blowing the wrong way - been there, done that !!

[H7OB]

Thanks chaps.
That was one of the first things that I checked and the rear mounted fan is drawing air rearwards.
I will double check with a piece of newspaper later though.

Ill try and get some more tension into the belt later though stocks are on back order at all the usuals. Great timing for a national 4.2 belt shortage!

[1954Etype]

What fan have you got?

Does the fan come on when you are moving?

Angus

[H7OB]

What fan have you got?

Does the fan come on when you are moving?

Angus

Hello Angus,
Its an aftermarket fan that works off a thermostat on the left hose on the expansion tank. Apologies, but I dont know the brand. I can take a look when Im home. It will come on when moving as well as with the manual override. I did wonder if once the relay had been changed it was running the other way but seemingly not. Im also thrown by the fact that it was working fine previously and does when the car is stationary, hence questioning the belt.
Many thanks

[1954Etype]

The fan shouldn't come on when the car is at temperature and running. You might have air in the system. When the car is cool, remove the cap (check it is a 7lb cap and is the correct depth - you should feel a slight resistence when you fit it as the lower seal engages with the header tank). Fill the header to the top and run the engine. Top up as required. Keep an eye on the temperature and when it is at normal, turn the car off. Fit the cap and run it again. Note that it will burp out what it doesn't need when you turn it off again. See if that cures it.

[H7OB]

Many thanks Angus. Ive recently replaced the coolant and dont think shes air-locked but Ill certainly give it a go.
Cheers.

[H7OB]

Well, belt seems tight and there doesn’t seem to be an air lock so I’m starting to think it might be electrical. The temperature change on the gauge seems to happen really rapidly, up and back down and it doesn’t seem ridiculously hot under the bonnet just after an indicated 110. I’m not sure what the symptoms of a failing temp sensor are but I’ll try that when it arrives.

[H7OB]

Or maybe voltage regulator as the fuel level seems to have stayed pretty high since I filled up and I understand from the forum that these run off the same... the plop thickens!

[H7OB]

So, fitted the new temp sensor, it’s not that! I’m now thinking/hoping it’s the voltage stabiliser. The theory being that it’s causing fuel and temp gauge to read over as the fuel level hasn’t gone down since I filled up recently and the temp gauge is reading high. Just waiting for the stabiliser to arrive so watch this space....

[ianfey]

My e type ran cool but in traffic got hot and would not cool down even with the electric fan on. Tried all the usual and air coming back off the fan. Turns out the fan was running backward but the air it pushed forwards was bouncing off the radiator so giving the wrong impression. Try getting the fan running and then kill the power and watch it slow down. The leading edge of the fan blade should be the direction of rotation.

[H7OB]

Result!
So, today I fitted the replacement voltage stabiliser from Caerbont Automotive, took her for a run and, guess what, perfect! Sitting at about a steady 75 degrees, rising when stationary but controlled nicely by the fan. The old stabiliser seemed normal when ticking over but the extra charge with extra revs sent it to the top of the dial. The fuel gauge was also over-reading too so the only negative is that I’m now down 1/4 of a tank!

Because of the recent rebuild I was super sensitive about such apparent high temps so glad it was never as hot as shown. The good thing is I’ve now had a full cooling system once-over including coolant, water wetter, correct thermostat, new temp sensor, fan once-over, over-ride switch etc. Many thanks for all the helpful replies, much appreciated!

The offending item...