QuestionI have a 78 Spitfire that has started to overheat after running it on the freeway. Typically the temp gauge stays at 3/4 when driving the freeway at 70 to 80 mph. Once I hit traffic or I enter the city the temp raises dangerously close to the Hot indication. I have flushed out the radiator (original one), replaced the thermostat from a 180 to a 160 as well as the temp sensor. This seemed to help but the problem is still there. Since then I have replaced the voltage stabilizer and readjusted the timing. Originally the timing was at 5 deg ATDC; I changed it to match the spec's listed under the bonnet to 2 deg ATDC using a timing light at idle with the vacuum disconnected. This made the engine run soother but the car still overheats in stop and go traffic. My father asked me to check out the fan clutch or the head gasket. Do you have any advice before I go any further? Is there something I am over looking? Any advice would be appreciated. Thanks!
AnswerCheck the front air dam to see if the front license plate is blocking airflow. Some have improved the cooling by removing the front plate, and making sure they have the air scoop and correct shrouds/valences to channel air into the radiator.
Also, the temp gauge is driven by the voltage stabilizer, at a reduced voltage (10v vs. 12v) Measure the voltage going to the gauge with the ignition on; if it is 10V, the stabilizer is fine.
If you have a color tune kit, or similar, you can check to make sure you don't have a lean mixture in the carb (stock CD-150, I assume), which can lead to over-heating issues; but you would almost also have pinging/detonation as well
As an experiment, take the thermostat out completely. If it still over-heats in these conditions, it is likely the combustion gasses are getting into the coolant (cracked head, block or blown gasket). You don't want to leave it out all the time, as the engine needs a certain temperature to be most efficient/powerful.
If you have a mechanic friend, most repair shops have a sniffer that they can put in the radiator fluid to check for CO or other combustion gasses. Other than the sniffer, there is no other real check you can do to see if the head gasket is blown. low compression may be an indication, but a connection into the coolant jacket isn't definately the cause.
With the thermostatic clutch on the fan, you should be able to hear it go on, and hear the change in pitch when it kicks in and out.
Below are some additional links for more information
http://www.triumphspitfire.com/gauges.html
http://www.canleyclassics.com/infodatabase.asp?article=overheating
http://www.spitfires4fun.com/5.html
http://www.kosier.net/spitfire/cooling.htm
Good Luck!
