View Full Version : Hot Cobra-----Help

18-05-05, 05:20 PM

Just become the owner of the 5.7 Chevy Dax Cobra, though I'd better get one whilst I could still climb in and out of it! Given that this vehicle is 10 years old and as per design, with good levels of oil water and electric fan working.It is running hot in traffic with the indicator nearly full over. Is this a design fault or is it worth fitting twin cooling fans to the rad. Any views appreciated

18-05-05, 06:15 PM
Welcome and enjoy your Cobra!

It could possibly be an air lock - where is your header tank situated?- Is it at the highest point of the cooling system?


Grease Monkey
18-05-05, 06:20 PM
Could you put a switch in parallel with the thermostart switch so you can override when the fan comes on.

Switch it on in traffic and leave it on and see whether this improves the temp level.

18-05-05, 07:10 PM
If it's 10 years old and probably been relatively little used in that time, the Radiator could be pretty bunged up. I would try flushing out the whole system. Flushing water through the various bits first one way then the other you will probably be amazed at how much crud comes out....
Nice little Sunday job in the Sun.....


clive a brown
18-05-05, 07:16 PM
It could be running lean

or a air lock

small bonnet air intake

or all three

Regards Clive

18-05-05, 08:11 PM
Not sure if this will help, but some times does.

1) Check that the thermostat is OK, one way is to put in boiling water and see if it opens?.

2) Check what the reading of the water temp sender is in boiling water to make sure that you feeling of hot running is correct.

3) Flush the system and put new water in, leave the top off the header, until engine is warm then thermostat should then open and you can top up. Also may want to put some water wetter in.

Anyway, just a thought.


18-05-05, 08:18 PM
Agree with all the above and would add that if you still find the car runs too hot you might want to check/replace the fan switch with one having lower temperature settings. That will enable your fan(s) to cut in earlier. Also exhaust wrap may help to reduce underbonnet temps.
However bear in mind that the bigger the motor the more heat it will generate and the more you may need to maximise cooling.
Enjoy :thumb: :thumb:

18-05-05, 09:36 PM
Before you do anything else - do the test that Hawk289 suggested - unscrew the water temp sender, and contrive to drop it into some boiling water (kettle is fine) and see what your dashboard gauge reads. These things can be exceptionally non-linear and uncalibrated.

Quite natural for water temps to rise in traffic, it could be that your gauge is "over-reacting" to this normal rise. Trying to "cure" the problem might be a waste of time, since it might not actually be a problem!

Purple AK
18-05-05, 10:16 PM
Fully concur with Wilfs comments :thumb: My gauge reads 120c-130c degrees all the time!! :mad: But if I run an infered thermometer over the rad and hoses the most it reads is 80c -90c :confused: These things are notoriously inaccurate ;)

18-05-05, 11:26 PM
Do you have Smiths instruments? i.e temperature and fuel gauge. If so they can read high if the regulator is not functioning properly.....they run off 10 volts.

19-05-05, 09:05 AM
Digital thermometers are about 10 quid from Maplins & cheaper than the infra red jobbies -saves any arguments about getting the domestic kettle all mucky too!

19-05-05, 09:10 AM

Thanks guys for all the suggestions and advice, some of which I've explored already as an electrical engineer. However, the reality check of others thinking the same, does save time, effort and money!!!! Appreciate it.

All your efforts does enable a "planned response" of what to do first (pick the easiest or most likely! ). I was also thinking along the same lines of "is it really hot or is it instrumentation?" to start with rather than pulling the thing to pieces first, as the accuracy of instrumentation must be in the varying trend rather than a definative value.

If when I've sorted thes line of investigations out.I was interested in the pictures of other Cobras with twin 9" fans fitted to the exteria of the rad, does anyone have them and find they help, or are just a costly adornment?

Thanks to all

Stevie Ray

19-05-05, 11:45 AM
If all the other suggestions don't help then I suggest that you put a bottle of water wetter in from Red Line. This works in simple terms by reducing the amount of bubbles in the system and giving you better heat transfer. Also the amount of anti freeze in your system makes a big difference. It reduces the heat transfer but lots of people keep it in due to the corrosion inhibition it gives. Water wetter works well and reduces the temprature by a 15-20 deg C. I run it in a GT40 to good affect and don't suffer the same overheating problems as cars without it. It also contains a powerful anti corrosion inhibitor to protect the heads, especially if they are alloy. I have been using it for nearly 10 years and have no signs of corrosion. I don't run any anti-freeze either.
Also if you are air locking then a seperate return line from the top of the rad to the header tank usuually sorts this out.
Demon Tweeks etc have the above product 15 ish

19-05-05, 08:57 PM
I had similar problem, thought running hot, it wasnt in actual fact, was the dial reading incorrectly due to a faulty earth cable. Replaced virtually everything, pulled my hair out, went even greyer and finally it cost me 3.69 for a new earth cable - problem solved! Nigel

Richard Gibbs
21-05-05, 07:59 AM
Just a thought on the rad bunged up idea. If you run the engine up to temp and then feel the rad you may find areas that are cooler than others indicating a blockage. Could be just a small fin or a group. Either way you'll be able to check easily. Also, if its 10 years old I wonder how many times the water system has been flushed through. Not many I bet. Probably worth doing.

If you look at the Dax build manual for the cooling system diagram you'll see they have a return pipe back to the header tank from both the rad and the water pipe that exits the engine. Not sure if the reason for this design is because they found problems like you were desciibing in earlier models. Helps the get air out of the system.