Overheating and operation of fans

[griff50tvr]

I've got a strange problems with the fans on my Griff - anyone got any ideas or had the same and sorted it?

My Griff overheated as my local TVR dealer in the county (who'll be nameless) did not reconnect the fans after replacing the air filter. After cooling down, connecting the fans and refilling, the fans seemed to switch on and off ok.

But after a few miles it seemed as though the fans were on continuously and, even after leaving the car overnight, the fans came on as soon as I switched on the ignition and they stayed on all the time, the engine running cold around 70 deg. After a couple of days or so, the fans started to switch again but not at the usual temperatures, staying on for longer than was usual. After a few more days, the fans no longer come on with the ignition and seem to be switching on and off at around the correct temperatures.

I can't find any logic to explain this unless the ECU (which I don't fully understand) is doing something smart to protect the engine following the overheating until it has learned that all is ok again. Can anyone explain what is going on and if this is correct / good operation ... and if anything might need repairing / replacing?


Also, in the bible it says the otter switch is on the bottom of the swirl tank. There are no electrics on either the swirl or expansion tanks on my Griff (late '99)! However there is an electrical connection on the top of the radiator nearside under the nose cone which is not shown in the bible. Could this be the otter switch / temp / fan sensor?

[geoffvalenti]

On the later Griffs the otter switch is located in the radiator side. Mine's on the top left when facing the front of the car. (1998)
Personally I don't think the ECU is "clever" enough to try things to sort out potential overheating problems.

If its any consolation, the fans on my Griff seem to be running a lot at the moment, but I'd rather put that down to the (good) weather we're experiencing at the moment.

Personally, I'd far rather it ran a bit cold than overheated this time of year, so I'm not thinking of trying to "fix" it

edit: to say if the fans are running all the time it may be a water level problem, I'm assuming you've checked and bled the sytem after it overheated?

Edited by geoffvalenti on Monday 5th June 16:35

[richb]

Indeed the ECU has nothing to do with the fans, they are on a pretty simply power circuit switched on/off with the ignition and then controlled by what is known as the "otter switch". This is a standard Lucas item that costs about £15 and looks like a brass plug screwed into the radiator. It only has two wires going into it - a simple test is to connect the wires with a paper clip and the fans should come on. The otter switch is basically a thermostat in the rad nothing more complicated. Whilst one would assume these either work or are busted I found that they can just go "on the blink" and work intermittently, this give the impression that the fans sometimes work and sometimes not. I reckon the first thing to do is swap the otter switch and see if it cure the problem. Rich...

Edited by richb on Monday 5th June 16:46

[cv1040]

You may already be aware of the ModWise kit to control the fans as well. With the single point of failure in the Otter switch and with Griff's being in need of any cooling help they can get I find the extra piece of mind the ModWise kit gives really valuable. As well as all the other cooling benefits.

Effectively when fitted you have 3 devices that can switch the fans on: the original otter, and 2 variable thermostats from the kit, typically set to come on before the otter even gets a look in. That's a lot of redundancy, but well worth it.

You should get to the bottom of your existing cooling problems first though as if you did go down the ModWise route you might be masking an underlying fault that needed clearing anyway.

Cheers

John.

[simpo two]

My 4.0 Griff did that just before I sold it.

[tvr_nut]

simpo two said:

My 4.0 Griff did that just before I sold it.

When my otter switch failed, it failed "to danger" - i.e. fans did not cut in and the car boiled over. I have since put in a new otter switch and an over-ride switch and fans-running LED, as per the Steve Heath Griffith Bible (once bitten always paranoid!). There is a lot in there about this subject BTW........

Heard Water-wetter can help keep the coolant temps down a bit (so fans are on less often) - am going to try it once I 've had the car serviced (after as it is due a coolant change then).

TVR_Nut

Edited by tvr_nut on Tuesday 6th June 08:55

[richb]

tvr_nut said:

When my otter switch failed, it failed "to danger" - i.e. fans did not cut in and the car boiled over.

That's the point I am making though, they don't always do this, they sometimes just go a bit intermittent...

[griff50tvr]

Thanks for the input. The otter switch on my Griff must then be the electrical connection at the top nearside of the rad. As this is likely the otter switch (and the side of the M20 was not the place to try bleeding the system after topping up(!)), could it be possible that there was an air gap at the top of the rad and the switch was indicating the temperature of steam rather than the water? And now, after some running and subsequent topping up, the air gap has gone and so it is switching based on the water temp again? It sounds almost possible (and logical). The Modwise kit sounds like a good idea but I agree that it is better to understand/fix any issue first rather than cover it up.

[FlipFlopGriff]

It may have warmed up but our fans are hardly coming on at all at the moment. Sits 75-80 on the motorway and stays just above 80 when stationery. Mind you the alley rad and Modwise kit help. Modwise kit puts the fans on 1/2 speed at around 85 which slows the overheating down. Normal fan speed then kicks in at 90 ish (but not very often now).
FFG

[richb]

griff50tvr said:

could it be possible that there was an air gap at the top of the rad and the switch was indicating the temperature of steam rather than the water?

possible I suppose, you should have a bleed tap at the topcorner of the rad...

[tvr_nut]

richb said:

tvr_nut said:

When my otter switch failed, it failed "to danger" - i.e. fans did not cut in and the car boiled over.

That's the point I am making though, they don't always do this, they sometimes just go a bit intermittent...

In reality my otter switch did not fail totally - it seemed to cut the fans in initially, but then they went on and off periodically. As the water temp went up, the fans spent more time off than on, until they stopped coming in at all, and it started to overheat. This meant my early diagnosis of the problem (in M6 roadworks) was difficult, as although running too hot, the fans were running when I opened the bonnet. It wasn't until the final boil-over I noticed they were stopped, and on testing discovered the strange intermittent behaviour.

The old otter switch must have been tired for a while, as although the replacement was marked as cutting in at a higher temperature (but was "the only one TVR use now" according to Dealer), it actually came in sooner according to the temperature gauge on the dashboard.

Having fitted the "fans running" LED, it shows how often the fans are in use. It is not just in slow/stopped traffic, but seems (on a hot day) to be any prolonged running at <40mph. Once you acceleate over 40, the temp seems to come down quite quickly and the fans are off. I suspect it is the effect of the numberplate on airflow?

[richb]

tvr_nut said:

richb said:

tvr_nut said:

When my otter switch failed, it failed "to danger" - i.e. fans did not cut in and the car boiled over.

That's the point I am making though, they don't always do this, they sometimes just go a bit intermittent...

In reality my otter switch did not fail totally - it seemed to cut the fans in initially, but then they went on and off periodically. As the water temp went up, the fans spent more time off than on, until they stopped coming in at all, and it started to overheat.

Ah sounds like mine then...

[donatien]

The otter switches are prone to failure, heat (oddly enough) can break them down. You can test the otter by leaving the car to idle after a blast and waiting for the fans to kick in, this should be around 90-95 +/- depending on the accuracy of the temp gauge. If it goes up to 110 without fans on then you likely have a duff otter so replace it. To test completely you can take it out and shove it in boiling/hot/warm/etc water with a multimeter but that seems hard work to me.

I assume you carry some spare blade fuses? If you get stuck en route you can short out the otter by putting a fuse between the two otter feeds, take the two terminals off and connect with the fuse (paper clips also work), it's only an earth circuit so there is little current. This gives you fans on all the time, so it will take power from the battery

The otter circuit then drives some relays (depends on the model as to where and how many that is) so it is also possible you have a dodgy relay. The relay in turn shoves power to the fans through main power.

Many owners have fitted an over ride switch so you can pre-empt heat issues. This is a switch in parallel with the otter and knocks the fans on as you wish. A common place to site this is the dash dimmer on/off switch. Not done it myself but am looking in to it

Dave

[tvr_nut]

In response to Dave/donatien, that is what I decided to do, although I did not the dash-dimmer switch as it is a bit dicky on my car. I tried it once thinking "what's this for" - it turned off the dash lights and would not re-latch! Took many presses before it stayed latched in the "on" position, so has been left well alone since.

I got a neat little circular rocker-switch from RS-Online that fitted under the column shroud instead. This is also slightly easier to get at when driving (not that I've really needed to use it since putting in new Otter switch).

Took about half-day to fit the system described in the SH Griff/Chim Bible (and a day to get over the backache!).

Edited by tvr_nut on Thursday 8th June 11:56

[griff50tvr]

I had the otter switch tested today and while it operates, it is not at the published settings apparently. So it looks like the overheating has disrupted its operation and a new otter switch is on the way. In the meantime, I've got a handy supply of paper clips!!

[landroverdan]

you should have rang the dealer and told them you overheated on the motorway cos he didnt connect the fans if a dealer makes a mistake complain like a b*tch it pays off (seen it done many times even when it wasnt the dealers fault)

[tvr_nut]

griff50tvr said:

I had the otter switch tested today and while it operates, it is not at the published settings apparently. So it looks like the overheating has disrupted its operation and a new otter switch is on the way. In the meantime, I've got a handy supply of paper clips!!

Whilst you have the coolant partly drained (although perhaps less comes out than with the otter switch on the bottom of the swirl pot?) it might be worth dropping in some water-wetter?

What are the experiences out there of this stuff - those who I have asked reckon it works well and reduces coolant temps by 5-10degC?

[griff50tvr]

landroverdan said:

you should have rang the dealer and told them you overheated on the motorway cos he didnt connect the fans if a dealer makes a mistake complain like a b*tch it pays off (seen it done many times even when it wasnt the dealers fault)

Unfortunately, I was in the outside lane at the end of the M20, watching the time rush by, trying to get to Dover for a ferry! But, for sure, the work is now being done by the main dealer.

[griff50tvr]

tvr_nut said:

griff50tvr said:

I had the otter switch tested today and while it operates, it is not at the published settings apparently. So it looks like the overheating has disrupted its operation and a new otter switch is on the way. In the meantime, I've got a handy supply of paper clips!!

Whilst you have the coolant partly drained (although perhaps less comes out than with the otter switch on the bottom of the swirl pot?) it might be worth dropping in some water-wetter?

What are the experiences out there of this stuff - those who I have asked reckon it works well and reduces coolant temps by 5-10degC?

Not sure about water wetter - I've seen something posted recently (can't remember where tho) which said there were some unwanted side effects (but again, can't remember what those side effects were - another senior moment!!).

[griff50tvr]

I had the new otter switch fitted today and the cooling system pressure checked etc.

The fans now switch more frequently and at a slightly lower temp range so it looks like this has sorted the strange operation of the fans.

Hope this helps anyone else with erratic switching cooling fans.