Cooling Fan circuit on a Tamora

[roseytvr]

Hi Guys
A recently acquired Tam has an LS engine and aftermarket ECU. Both fans are kicking in at 90 degrees according to the ECU (85 degrees according to the dash) I haven’t quite worked out the intricacies of the ECU yet to look at its settings but strangely:

Both Fans come on at the same time but do not go off unless I turn off ignition regardless of temperature drop.
If I pull one fan relay both fans keep going but go off if I pull both relays, same with fuses, both out it stops but either one out both fans keep running.

Any pointers or tips? I had assumed the two fans were on separate circuits and could be set to come on at different temperatures - clearly not the case with my set up. Given this has a bespoke ECU and loom is it likely I am looking at a wiring fault or anything else I should be checking? Not to bothered at both fans working at the same time but certainly would like them to cut out as water temps drop. Obviously I will check the settings in the ECU as soon as I get to grips with the software.

Thanks

Ian

[TV8]

Hi Ian, how are you? It looks like you are collecting TVRs! Do you still have the Griff?

Mine is gone and replaced with a 996. It’s going to be interesting not having a convertible for the summer but i will cope!

[spitfire4v8]

You could pull the relays out and do a continuity test from the relay socket down to the fan positive feeds .. you should only have one fan powered per relay so if you can get continuity to both fan positives from one relay output then they've been joined somewhere.
Also continuity test back from the fan signal earth back to the ecu, do you have two separate signals or have they been joined somewhere ?

If you wanted to (and to get the best power to the fans) you could do away with the tvr relays in the fuse box and have 2 separate relays taking their power direct from the starter motor and signalled individually back to the ecu, that would guarantee you have separated circuits and maximum power from the starter motor big cable.

presumably the ecu adjustable parameters are in cal > output functions > fan 1 or fan 2

90 degrees could be close to thermostat temp if your temp sender reading is off, though I'd be inclined to trust the ecu sender more than the dash sender, but either / both could be out .. and is the ecu coolant temp calibration table correct?

[Penelope Stopit]

As above

There's a good chance that the circuits have been linked to overcome a 1 or 2 fan failure

Regarding fans staying on once they've cut-in

An incorrect or incorrectly wired relay will hold in once pulled in

There's also the problem of relay pullin and hold-in voltages

Many relays will pull-in at 7 to 8 volts and hold-in until the voltage drops to 5, 4 or eve 3 volts

Hence a low voltage across a relay winding will hold its contacts closed

[s6boy]

Or trinary switch?

[roseytvr]

TV8 said:

Hi Ian, how are you? It looks like you are collecting TVRs! Do you still have the Griff?

Mine is gone and replaced with a 996. It’s going to be interesting not having a convertible for the summer but i will cope!

Hi Graham,

Very well mate thanks, hope all's well with you.

I am using my home time to sort out all things TVR. The Cerb is gone but I still have the Griff and Sag and have added the Tamora to the collection! Once I get the Tamora fully sorted (I am having electrical issues at present) I may move one or both of the others on. That said they are both running great at the minute so it may be a difficult decision. I have finally had the Griff properly mapped with the decat pipes and the performance is awesome but I do fancy prepping the LS in the Tam to see what I can get out of it.

How are you getting on with the 996? Not sure you will get many miles in this summer mate the way things are going.

Keep safe

[roseytvr]

Thanks for the input chaps. I've not had much chance to look at it today as I may have cocked up the settings in the ECU trying to get in to it and have spent most of the day looking at that. Net result I cant start it (FFS) so I need to get some help from the ECU manufacturers if I can.

I have noticed that there is an incorrect relay in the fuseboard for one of the fans so I will get this changed first and then check all other possibilities.

[Penelope Stopit]

roseytvr said:

Thanks for the input chaps. I've not had much chance to look at it today as I may have cocked up the settings in the ECU trying to get in to it and have spent most of the day looking at that. Net result I cant start it (FFS) so I need to get some help from the ECU manufacturers if I can.

I have noticed that there is an incorrect relay in the fuseboard for one of the fans so I will get this changed first and then check all other possibilities.

Nice find with the relay, good start

[roseytvr]

Ok so a couple of weeks on....
I managed to recalibrate the ecu and lose all settings. Fortunately I traced down the mapper who had a back up and recalibrated. The ecu fans were set incorrectly and a quick tweak has them cutting out at 89 degrees.

The two fans are indeed looped at the fuseboard. Net result two fuses and relays powering what is now a single loop.

The fuseboard joins are awful and need to be redone



So:
1 any ideas why someone would link the two circuits?
2 Is it a problem having two feeds to effectively a single circuit
3 any real benefit having two separate fan settings?

Thanks

[Penelope Stopit]

roseytvr said:

Ok so a couple of weeks on....
I managed to recalibrate the ecu and lose all settings. Fortunately I traced down the mapper who had a back up and recalibrated. The ecu fans were set incorrectly and a quick tweak has them cutting out at 89 degrees.

The two fans are indeed looped at the fuseboard. Net result two fuses and relays powering what is now a single loop.

The fuseboard joins are awful and need to be redone



So:
1 any ideas why someone would link the two circuits?
2 Is it a problem having two feeds to effectively a single circuit
3 any real benefit having two separate fan settings?

Thanks

Someone would link the fan circuits because one had failed or that they wanted them both kicking in at the same temperature

Yes, linking 2 supplies to one circuit could cause big problems if a fan motor started getting tight and drawing too much current, the thing is I don't know how the circuit supplies have been fused and wired

But....

Even without knowing how those circuit supplies are wired, 2 fans connected to one relay and possibly drawing all the current through 1 fuse is itself a big problem

If you do decide to have both fans kicking in together

Wire fan 1 to relay 1 and fan 2 to relay 2, then make sure that each fan relay supply has its own fuse or each fan relay output has its own fuse

Then you could loop the ECU fan relay 1 control cable to the fan relay 2 coil terminal and tape up the ECU fan relay 2 control cable

Before linking the ECU fan relay 1 control cable to the fan relay 2 coil, you would need to know that the ECU fan relay 1 control circuit will drive 2 relays rather than1 (current draw of relays is very low but you still need to know)

If you can't find the specification for the ECU fan relay control outputs (What maximum switching current is) you could wire a 3rd relay, switch relay 3 with the fan 1 ECU control cable and wire its contacts to switch fan relays 1 & 2 on and off

[non_linear]

I strongly agree with what Penelope says. The other problem with both fans going through one fuse is if one motors fails and takes the fuse out, then you have no fans.

I don't know what aftermarket ECU you have, but if it has twin fan control lines(or a spare output for the second fan) could you program it to give you what you want?

[roseytvr]

Thanks for your input chaps. Decided to cut it all out and put back to standard. All the soldered joints were iffy and I had established both fans work powered independently. I need to make sure the cabling to the ecu is correct then change the map to fan 1 and 2. If there is a problem doing this with the ecu I can always modify it correctly at a later stage.

TVR ownership is a quick learning cycle, now back to the alarm cabling!!

Edited by roseytvr on Sunday 12th April 21:44

[Penelope Stopit]

roseytvr said:

Thanks for your input chaps. Decided to cut it all out and put back to standard. All the soldered joints were iffy and I had established both fans work powered independently. I need to make sure the cabling to the ecu is correct then change the map to fan 1 and 2. If there is a problem doing this with the ecu I can always modify it correctly at a later stage.

TVR ownership is a quick learning cycle, now back to the alarm cabling!!

Good decision

Nice that you were able to prove the circuits are working correctly

No doubt the fan fuses will be checked and the correct ones fitted

Keep well

[roseytvr]

Penelope Stopit said:

Someone would link the fan circuits because one had failed or that they wanted them both kicking in at the same temperature

Yes, linking 2 supplies to one circuit could cause big problems if a fan motor started getting tight and drawing too much current, the thing is I don't know how the circuit supplies have been fused and wired

But....

Even without knowing how those circuit supplies are wired, 2 fans connected to one relay and possibly drawing all the current through 1 fuse is itself a big problem

If you do decide to have both fans kicking in together

Wire fan 1 to relay 1 and fan 2 to relay 2, then make sure that each fan relay supply has its own fuse or each fan relay output has its own fuse

Then you could loop the ECU fan relay 1 control cable to the fan relay 2 coil terminal and tape up the ECU fan relay 2 control cable

Before linking the ECU fan relay 1 control cable to the fan relay 2 coil, you would need to know that the ECU fan relay 1 control circuit will drive 2 relays rather than1 (current draw of relays is very low but you still need to know)

If you can't find the specification for the ECU fan relay control outputs (What maximum switching current is) you could wire a 3rd relay, switch relay 3 with the fan 1 ECU control cable and wire its contacts to switch fan relays 1 & 2 on and off

Whilst I have now down the repair I am intrigued as to the why do it. The two lives from the fuse board effectively fed both Fan 1 and Fan 2 circuits ie cable out of fuse board for Fan 1 (after relay and fuse) went to both fan circuits, likewise cable out of fuseboard for fan 2 (after relay and fuse) went to both fan circuits therefore you could take either of the two relays out or either fuse and both fans would still work. Why would you do this? When I say intrigued its not keeping me awake at night!

[Penelope Stopit]

roseytvr said:

Whilst I have now down the repair I am intrigued as to the why do it. The two lives from the fuse board effectively fed both Fan 1 and Fan 2 circuits ie cable out of fuse board for Fan 1 (after relay and fuse) went to both fan circuits, likewise cable out of fuseboard for fan 2 (after relay and fuse) went to both fan circuits therefore you could take either of the two relays out or either fuse and both fans would still work. Why would you do this? When I say intrigued its not keeping me awake at night!

Good question

There are only two possibilities as to why

There was or is an intermittent fault on one or both fan circuits (possibly a relay, fuse-box internal link or burnt plug)
Linking the supplies is a very cheap way of overcoming what could be an expensive problem to find

or

Have both fans run at the same time (hot days? overheating problem?) without having to think much