Overheating

[Biggles1964]

Well still so far so good with my purchase, except?
Went to Diss and back good loop twisty bit on the way there collected brother in law. He doesn't li,e fast twisty bits so came back on the dreaded A 140. Lots of start stop traffic, anyway the beast got a little warm by the time I got home very warm bit no warning g lights or buzzers.

Lifted the bonnet to make sure fans running, couldn't believe it. When upgraded rad and fans fitted (previous owner) some numptie wired smaller fan negative to positive so fan was running backwards. Chucking hot engine bay air through the rad!

Now wired correctly, questions at what temp does second fan kick in?

[CerbWill]

93 & 95 as standard. Unplug the water temp sensor if you want to check they both run.

[ukkid35]

CerbWill said:

93 & 95 as standard. Unplug the water temp sensor if you want to check they both run.

If the ECU has had the fan cut mod to ease load when starting, then the engine has to be running for this test, not just ignition on

[Biggles1964]

I wondered why fans wouldn't run unless engine was running.

[Byker28i]

ukkid35 said:

CerbWill said:

93 & 95 as standard. Unplug the water temp sensor if you want to check they both run.

If the ECU has had the fan cut mod to ease load when starting, then the engine has to be running for this test, not just ignition on

Then a mod also to bring the fans in earlier and also be aware that the fans are controlled by the ECU. Because of the way the water temp capillary tube runs to the gauge then it can read anywhere from 5 to 10 degrees higher, so if checking fan operation, use one of the diagnostic tools to check temp. Most also have indicators to tell you the fans are commanded on.

[spitfire4v8]

OP take a pic of inside the ecu and I will tell you if it has had a lower fan temp chip at any point.

[Biggles1964]

Thanks for info byker, when I purchased the car it came with a massive folder including invoices. In the information the previous owner said the temp gauge read appx 13 degrees higher.

I found invoice for the rad upgrade including 74 degree thermostat (shame they didn't know how to wire them correctly)

Another invoice from kits and classic, for cooling chip, fan 1 on 90c off 85c fan 2 on 92c off 87c fans on over 400 rpm

I took it out for a good blast and all seemed fine temp stayed at acceptable level, it was fairly difficult to get second one to kick in. The first fan almost seems to be spinning faster now second fan correctly connected?

[Austin Seven]

There is no wiring to the thermostat; it is the device which physically opens (in a controlled manner over several degrees) once the coolant exceeds a certain temperature, to allow the coolant circulating around the engine to pass through the radiator. This is the device which you have that operates around 74 degrees C.

There is some debate currently in the Chimaera forum here https://www.pistonheads.com/gassing/topic.asp?h=0&... about thermostat operating temperatures, which you may find interesting.

The wiring for the fans is controlled by other thermal sensors which have electrical connections. I'm not familiar with the details of the Cerbera so I'll leave it here.

[TwinKam]

Austin Seven said:

There is no wiring to the thermostat; it is the device which physically opens (in a controlled manner over several degrees) once the coolant exceeds a certain temperature, to allow the coolant circulating around the engine to pass through the radiator. This is the device which you have that operates around 74 degrees C.

There is some debate currently in the Chimaera forum here https://www.pistonheads.com/gassing/topic.asp?h=0&... about thermostat operating temperatures, which you may find interesting.

The wiring for the fans is controlled by other thermal sensors which have electrical connections. I'm not familiar with the details of the Cerbera so I'll leave it here.

The OP didn't say that the thermostat was wired incorrectly, rather that the fans were.

[Austin Seven]

TwinKam said:

The OP didn't say that the thermostat was wired incorrectly, rather that the fans were.

It seemed to me that he did suggest that, when he wrote:

I found invoice for the rad upgrade including 74 degree thermostat (shame they didn't know how to wire them correctly)

so I thought he was confusing the (coolant control) thermostat with the thermal sensor for the fans.

[ukkid35]

Austin Seven said:

It seemed to me that he did suggest that

Me too

That thread is interesting, though too long to read in full

I agree with ChimpOnGas, there is no advantage to fitting a 74C thermostat, and there are significant disadvantages, which begs the question: why are they even available?

Also worth bearing in mind that the AJP8 Cerb does not have an oil stat fitted as standard (don't know whether that is true for S6 cars as well), so the engine will take longer to reach operating temp than is should anyway

I was told that there was a German owner who used his Cerb all year round for commuting, and he lived only a kilometre from the autobahn

He had a couple of engines replaced under warranty before TVR discovered how the car was being used, meaning it took a very long time to reach operating temp, especially in the winter

[Biggles1964]

Sorry for confusion, I meant the second fan was wired negative to positive so when fan fired up it dragged hot air from engine bay through the rad. Although I guess physics would say air coming through rad from driving at x mph would have to be greater than fan air movement to have any effect. So guess to a certain extent it was neutralised. Now that does sound confusing. It may also explain why air con was not ultra cold but is now working fine.

Think I may just have to go out for another blast just to double check all is ok :-)

[Austin Seven]

ukkid35 said:

That thread is interesting, though too long to read in full

I'll save you time: the page I linked to, and I think the following page, contains pretty much all the debate on thermostats so far. The main thread is concerned with solving a temperature gauge under-reading issue, which is not relevant to the Cerbera, but I thought the bit on thermostat ratings might be of wider interest.

[aide]

As an aside, the water temperature sensor that feeds the ECU is in a really vernurable place and gets wet.
The stat terminals get corroded and build up with green oxidation on the spade terminals.
If the ECU looses its water temp feed it defaults and turns the fans on.
However, I found that with the oxidized terminals, the ECU receives an intermittent temperature feed which causes the fans to turn on less than is required to reign in the coolant's temperature and it slowly creeps up...

So I got a little flat file and cleaned the green oxidation off the stat terminals (right back to copper again) and filled the connector with Contralube before reconnecting. It's been good for 8 years now.

[VYT]

Biggles1964 said:

Well still so far so good with my purchase, except?
Went to Diss and back good loop twisty bit on the way there collected brother in law. He doesn't li,e fast twisty bits so came back on the dreaded A 140. Lots of start stop traffic, anyway the beast got a little warm by the time I got home very warm bit no warning g lights or buzzers.

Lifted the bonnet to make sure fans running, couldn't believe it. When upgraded rad and fans fitted (previous owner) some numptie wired smaller fan negative to positive so fan was running backwards. Chucking hot engine bay air through the rad!

Now wired correctly, questions at what temp does second fan kick in?

Probably just wired the replacement fans as the original was. My '96 4.2 was reversed.

[morebeanz]

aide said:

As an aside, the water temperature sensor that feeds the ECU is in a really vernurable place and gets wet.

Is that the terminal by the radiator on the passenger side of the engine bay? If not, could you give us a clue, please?

I've often wondered whether my fans always operate correctly...

[Byker28i]

Just back from France, driving around in temps of 37C plus. The car didn't go over 95 on the gauge, so it's possible...

[Mr Cerbera]

RaceTech have obviously hear your plea.

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