Profile of the Survey Sample
Sample size: 31, of which:
Griffiths: 17
Chimaeras: 14
400s: 12
4.3s: 11 (including two BVs and one 1994 4.3 HC)
500s: 8 (all 1994 or later)
All years were represented, but biased towards the older ones (ten 1992 cars down to three 1996 cars). I had intended to speak to a number of dealers, but after the first one confirmed most of the survey results I decided to stop at that point. The dealer's comments are included below.
I also asked what the temperature gauge was saying when owners felt their car was overheating. The answer varied between 95 degrees and 'off the dial', but the average was 100. The dealer's opinion was that the fans should cut in at 100 degrees on the ECU sensor. The fan otter switch (again in a different location) should cut the fans in at 98 degrees and switch them off again when the temperature drops to 93 degrees, but this may not be exactly what the temperature gauge is showing.
Twenty four of the owners' cars had overheated at some time, the other seven hadn't. Fourteen of the 'overheaters' didn't report any signs of the car being too hot apart from the reading on the temperature gauge. The dealer I spoke to services about 300 cars on a regular basis, and he guessed that up to a quarter of them had reported an overheating problem at some time. This really was a guess and needs to be interpreted in the light of other comments below.
With a couple of exceptions, overheating in the owner survey had been confined to hard driving or heavy traffic in hot or mild weather. The dealer reported a similar experience, with overheating confined mostly to town driving.
Classification of CausesThere were thirteen faults of this type (40% of the total).
- Five incidents of overheating caused by thhe wrong pattern thermostat or fan otter switch.
- Eight incidents of low coolant level or aiirlocks.
The dealer believed that at least 80% of overheating problems fell into this category, the rest being spread fairly evenly over the other categories below.
Tips
- Check the coolant level every week (yes, rreally - if something's on the blink the sooner you find out the better).
- At the same time, look around for visible signs of leaks, particularly at hose junctions, and check for frayed or perished hoses and loose or pinched hose clips.
- Don't top up with plain water. The antifreeeze in an aluminium engine prevents corrosion and things can silt up pretty quickly if you let the concentration drop.
- Get the system pressure tested if you susppect there is a leak but can't find it.
- If the heater isn't working well, one or mmore hoses feel cool or soft when the engine's warm, or you hear a gurgling/wooshing in the passenger footwell, you may have an airlock in the system. Bleeding it is not difficult, but be very careful when putting the brass plug back in the rad as it's easy to cross the thread and it's a real pain to repair.
Owners reported nine faults of this type (30% of total).
- One pressure cap leak.
- Five cases of faulty fan otter switches (mmostly on 4.3s and/or cars over three years old)
- Three cases of faulty thermostats.
This doesn't quite agree with the dealer's experience, who said that faulty thermostats were extremely rare.
Tips
- The correct thermostat is an 82 degree uniit with a large orifice. This is not a standard Range Rover part. The opening temperature
should be stamped on the thermostat. You can test it in a saucepan with a thermometer to see when/whether it actually opens.
- If the fans don't cut in above about 90 deegrees, try the following:
- Sound the horn. If it doesn't work this maay mean the fan fuse has blown, although not all cars have the fan and horn on the same fuse.
- Take the wires off the fan switch at the bbottom of the swirl pot and connect the terminals together. If the fans don't start when you turn the ignition on, there is a fault in the fan fuse, the relay (which is on the main panel in the passenger footwell) or the switch itself.
- Wiring faults are very unlikely unless sommeone has been messing about with things.
- The fan (otter) switch is easy to replace but make sure you get the correct 98/93 degree unit and don't try to do it when the engine's hot!
Tips
- A shrieking drive belt may only mean it neeeds adjusting, but it may also mean the pump bearings are on their way out.
- Radiator leaks are not always detectable iin a pressure test, but you should see the signs if you take the grille off as coolant collects there.
- The radiator, by the way, is a standard raange Rover part with a modifed bottom hose elbow.
- One of these was solved by the owner fittiing a fuse for each fan.
- One was solved with factory mod to staggerr the two fans starting up.
- The other three cars were still overheatinng.
One car's overheating was solved by fitting a bigger radiator.
One was solved with a manual fan override switch.
Tips
- The cooling system has been modified in smmall ways more or less continuously since the Griffith was launched in 1992. By mid 1994
when the serpentine engine came in, there was more than enough 'margin' to cope with the worst UK driving conditions. Attention
since then has focussed mainly on tropicalising the cars for the far east market, where sitting in a traffic jam in mid 30s temperatures
with the aircon running full blast places much greater demands on the system. Changes made for the Malaysian cars have been incorporated
in the UK models as well.
- If your fan fuses keep blowing, ask a dealler what can be done about it. More powerful fans (with 40 amp slow-blow fuses) were fitted around late 1994 to early 1995, and twin fuses in 1996. It's possible your car has acquired one without the other.
- 1997 cars have a shroud around the fan (ottter) switch to protect it from exhaust heat. Otter switches aren't that reliable at the best of times, and maybe this would solve the problems owners have reported here.
- The factory did offer a twin relay wiring harness for the fans a year or so ago, which cut the fans in one after the other to reduce the load on the fuses. Later modifications may have made this unnecessary, but I would imagine it is still available.
This is certainly inconsistent with the amount of discussion about overheating that takes place within the internet mailing list, and with the perception a lot of potential buyers seem to have about problems they might expect with their first TVR. I can only assume that we are dealing with a prejudice carried over from earlier TVR models. Prejudice being what it is, people tend to look for things that support what they believe and ignore things that don't.
From the responses received, I can find very little evidence that a well maintained car with the correct parts fitted should suffer from overheating. If it does, it is most likely to be the sort of problem that would be picked up during a routine service.
There are some pointers towards 4.3s being a little more prone to overheating, but this may be as much to do with their age as anything else. Common sense suggests that the first versions of any car might not be as well sorted as later ones, and that the more highly tuned versions might be a bit less forgiving in heavy traffic or if their cooling system isn't in top-notch condition. The survey doesn't provide any information on the effects of air conditioning, but it seems obvious to me that the stess imposed by this is not going to be kind to a cooling system that's a bit below par.
1. Is the car really overheating, or just displaying a high temperature on the gauge? It's worth getting a garage to check this, because I've had a faulty gauge in the past and got all upset about nothing. We'll assume that the gauge is accurate.
2. If the fans are not cutting in until the gauge is into the red, but the temperature does go down once they are running, this suggests that the otter switch is operating at too high a temperature. There could be two reasons for this:
a. The switch is faulty. In this case replace it with one of the original pattern.
b. The switch is operating within spec but the spec. is no longer appropriate. On the Chimaera the otter switch is in the swirl pot (millimeters from the exhaust) while the gauge sensor is in the block. Something may have happened to change the relationship between the temperature at these two locations, so that the poor old otter switch is doing its job properly but it no longer has the desired effect. There are some thoughts on this possibility below. In this case you will need an otter switch with a different temperature range.
3. If the fans are cutting in when they should but they don't pull the temperature down, then you have a cooling system which can't dissipate the heat being produced by the engine. Getting the fans to cut in at a lower temperature isn't going to cure this. Again, it could be because the system is malfunctioning, or because a different system is needed for current conditions.
a. The cooling system could be under-performing for a variety of reasons, all of which should be fairly easy for a garage to diagnose and remedy. The most obvious ones are:
i. Tired fan motors not shifting enough air. The motors themselves may be worn out, or there could be poor electrical connections. Try a direct connection to the fans from the battery and see if they run faster. See if someone else's fans run faster than yours.
ii. Leaves or similar obstructing the air flow through the radiator.
iv. Gunge in the radiator core, cylinder block or hoses. Get it flushed. If still unsure, get the radiator dismantled, as blocked rads are very common.
iii. Minor leaks (hose clips, radiator cap, radiator itself) causing a drop in coolant pressure. This allows the water to boil and froth can't carry the heat away properly. Might not be enough to produce noticeable coolant loss. Get it pressure tested.
iv. Clapped out water pump or drive belt slipping. Listen for squeals and rumbles.
v. Thermostat stuck closed. Shouldn't be possible, but test it in pan of water.
vi. Too little antifreeze (lowers the boiling point again). Get it checked.
vii. Air locks in the cooling system. Bleed it.
b. Different conditions could have occured because:
i. Modern fuels produce more heat. A lot of classic cars have overheating problems for this reason. The result might be general overheating, or localised hot-spots in the cooling system (eg. near the heads and exhausts) which the otter-switch can't pick up.
ii. Driving conditions have changed. New cars (even TVRs) are designed with long traffic jams in mind, but earlier models might not have been.
iii. The engine is not running properly (timing wrong, weak mixture, head gasket leak, etc., etc.). Serves you right.
There is no point in fitting non-standard components in an attempt to mask a fault in the cooling system, so the first step is to
check the items in 3a. If (and only if) the system is performing as is was designed to, you may have to consider modifying it.
The easiest mod is to replace the coolant with the pre-mixed stuff that racers sometimes use, as this will conduct more heat to the
radiator. The next easiest is to get more airflow through the radiator, by moving obstructions or by fitting bigger fans. Bear
in mind that the airways to a radiator are sometimes designed with constrictions to speed up the airflow, and removing these
might make things worse. The third option is to fit a high capacity radiator. Once the cooling system is capable of dissipating the
heat under all conditions, you can start fiddling with thermostats and otter switches to RESTRICT the operation of the system.
Peter Beech
Internet Mailing List Oct 96
I am getting paranoid about how hot my S3 apparently gets in traffic before the cooling fan cuts in. It doesn't get above the white
line and never into the red, but I'm sure I read an article some time ago saying the Ford V6's prefer running cool. Also the engine
feels a bit "woofly" when it is this hot. Does anyone know if there is a different fan switch that I can use? Reading
the Chimaera/Griffith notes that Peter Beech produced it is apparently called an Otter switch and alternatives are available for the
V8 engine - is it the same switch on the S3?
Mike Jennings
Internet Mailing List Apr 97
Is the otter switch next to the weasel filter or the stoat flange?
Andrew Cliffe
Internet Mailing List Oct 96
It sounds that your S3 is running fine if it stays at the 90 degree temperature level and does not move into the red. Both the S1
and S2, I had stayed at 90 degrees religiously with the fan coming in and out every few minutes.
I fitted an override switch to my S1 as an insurance policy and found that switching the fan in earlier did not make that much difference. The reason was that the temperature that the dial measures is that of the water circulating in the block and not the radiator. The thermostat essentially controls this temperature and only allows water through the radiator at about 85 degrees (this is off the top of my head). Having the fan switch in earlier will reduce the water temperature in the rad but not necessarily in the engine block. The cooler rad will help when the thermostat opens but the benefit may not be worth it. If you want to run your engine cooler, you will need to change the switch and the engine thermostat as well.
The best solution is to use one of the variable thermocouple type stats. Lotus used them on the Elan and I got one several years ago for about £25. These allow you to change the on off temperature and are pretty reliable. The cheapest option is to put an override switch and light inside the car so that you can see when the fan has switched in and switch it on at any point. By using piggyback connectors, the original wiring can be left as it is. The Sprint article I wrote gave the details. You can then play at being a human thermostat and work out if you need to change the stat.
By the way, you don't have to change the thermal switch. You could wire a second in parallel - the first one to reach the opening
temp will start the fan. If this then fails the second one will kick in at a higher temperature. And if you have the switch as
well then you can override everything. Just because I'm not paranoid doesn't mean they aren't out to get me . . .
Steve Heath
Internet Mailing List Oct 96
Thanks for your thorough and very helpful response! I agree that my cooling system seems to be working to spec., it's just that
horrible feeling in the back of your mind when you glance down and see the temperature gauge is higher than you thought. I fitted
a supplementary fan switch to my Caterham as this used to run slightly hot (Caterham subsequently doubled the depth of the rad,
so I think they were admitting that it was marginal). I also found that a shroud between the radiator and the nosecone (rather than
big gaps) directed the flow of air through rather than around the rad. I guess the above is a bit of a divergence from the TVR,
but perhaps it explains my concerns - I would rather have a "safety margin". Also, are there lower temp thermostats available,
and who from?
Mike Jennings
Internet Mailing List Oct 96
As for changing the stat, a good motor factor should have a selection . . . but I am really not sure that it is worth considering to
give you the safety margin . . . The reason is that the thermostat will already be fully open and therefore the running temperature
will be set by the thermal equilibrium - as Peter Beech said in his contribution - and will continue to be 90 degrees. The only
real way of gaining some benefit would be to increase the efficiency of the radiator by increasing its size, cleaning it and pushing
more air through it - i.e. fit a second and/or bigger fan. Kenlowe do make bigger and faster fans by the way.
The most important aspect is to ensure that the whole system is in A1 condition and fit the override switch and fan light to give
the safety margin and the feedback that the fan is actually working. If the temp starts to go up over 90 degrees and the fan has not
come on, then you have a problem and a few minutes to do something about it . . .By the way, the V8S runs cooler at about 70-80 degrees
but still goes up to 90 degrees when stationary in traffic despite having bigger air intakes in the bonnet, a bigger radiator, a
bigger fan and pints more coolant
Steve Heath
Otter switches are generally unreliable and if they pack up the fans won't come on at all. A get-you-home fix is to unplug the connector and join the two spade terminals together with a short piece of wire. This fools the fan relay into thinking that the otter switch is on, and the fans will run continuously. It might be worth doing this for a whole journey if the weather is exceptionally hot. V8 MGB owners routinely run longer versions of this wire to a manual over-ride switch on the dashboard and flick it on at the first sign of a rise in temperature. The reasoning behind this is that a marginally effective cooling system can often stop the temperature going up any further but may not be able to actually bring it down. The driver can react to the rate of change in temperature (and predict overheating) whereas a 'stat can only react to what has already happened.