http://www.nichols.nu/tips.htm

 

Thanks

 

feel the radiator when its hot and getting over hot, see what the heat distribution feels like on the surface up and down . if you have cool spots, it could be air in the system, water pump shaft slipping, and of course, rotted/cloged radaitor core. you can check the t-stat in boiling water and see if it opens, but of course, the radiator temp test will tell this. sticking t-stat is not that uncommon. mine doest it periodically, and the problem, it overheats, but the fans dont come on as the radiator is still cold! after heat soaking the engine t-stat, (turn it off for a few seconds) it opens and all is good for the day.

mk

MK

 

The early cars there is a thermo switch on the receiver drier in front of the radiator which when it senses heat in the freon turns on the auxillary fan (blower). It is worth noting that Porsche groups that fan with the A/C parts because it is NOT INTENDED to cool the radiator BUT is there to cool the freon in the A/C system. Porsche did fit an extra thermo switch in the bottom front of the left side radiator tank and at about 3/4 on the temp guage it will kick on to HELP. But the main cooling fan is the belt driven viscous clutched fan on the front of the engine positioned inside the shroud so it pulls air through ALL OF THE RADIATOR ! The helper blower in front only "cools" a small part of the radiator. The best TEST of the fan clutch is let the car idle until the helper fan comes on....then still not driving rev the engine up to about 3,000 RPM and hold it there for a couple minutes. If the coolant temperature drops and the electric fan goes off then you have a good indication that the fan clutch is not moving enough air. Same conclusion if the car runs cool on the highway BUT gets hot in slow traffic ...not enough air flow.

 

The best TEST of the fan clutch is let the car idle until the helper fan comes on....then still not driving rev the engine up to about 3,000 RPM and hold it there for a couple minutes. If the coolant temperature drops and the electric fan goes off then you have a good indication that the fan clutch is not moving enough air.

Jim,
I don't quite follow the logic here. If the temperature drops and the fan goes off doen't that mean it is working??

 

Roger ...I guess at least one person is reading my posts ...You are correct it seems counter intuative but the higher engine speed is spinning the fan faster at higher RPM and that is fast enough to get minimum air flow. But at idle speeds the slipping is so much that there is not enough air flow. Also worth noting that at the 3,000 rpm you are making more heat than at idle but with the additional air flow the rest of the cooling system works OK.

 

as a side note, if the fans come on , thats a good thing. this means themostat is working, but no guarantees on the quality of the flow inside the engine or radiator. if the fans can actually make the temp drop, thats also good. if they make the temp drop enough to make the fans turn off, EVEN BETTER> however, if you still have over heat issues, its a flow problem, probably due to the radiator, waterpump or some clog in the engine or an engine issue (blown head gasket) . blown headgasket , can heat up the water more than the fans can cool throught the radiator. check for over pressure in the overflow tank.

all of my overheat issues have either been clogged radiator, broken waterpump, or air in the system, not flowing properly, or sticking thermostat.

If you feel the radiator when its over heating, and its hot up and down, then that means the water is circulating, but may not be able to be circulated properly. the primary fan is most important. when i added a electric fan where the driven fan was, i used both the AC fan and electric fan to cool the radiator, and it worked well. (but i also removed the ac condenser) a push pull set up worked well for cooling.

mk

MK

 

Justin,
Did you find a solution?

Had to leave mine until now due to SITM and vacation.

Just noted some temperatures to see if anyone had any comments.
Car was at operating temp after a 10 mile drive in 100F ambient.

Idling on the drive the guage climbed to the 3/4 mark and the aux fan cut in.
Temp for the inlet hose to the rad.
Engine housing = 217F
Mid point on Hose = 206F
Hose where it enters the rad = 210F
Top of Rad Passenger side = 230F
Bottom of rad same side = 213F

Top of rad drivers side = 203F
Mid point of rad drivers side = 191F
Bottom of rad drivers side = 184F
Return hose at connection to rad = 206F
Mid point on return hose = 208F
Engine housing for return hose = 209F

The fact that the temperature is 184F at the rad before the return tells me the rad is operating OK ??
The fact that the temp increases from the return pipe is strange.
Any thoughts anyone?

Thanks,
Roger

 

IMHO, I don't think you have an overheating problem, considering the ambiant temperature. Also, what did you use to measure these temps? The numbers are suspect if the fan was on during the measurements. Accuracy of all measurements is suspect unless you're using a fully submerged sensor in the coolant flow. The IR thermometer can be misleading (especially in 100 degree ambiant or when being blasted by air from the fans).

One last test I recommend is to disconnect the radiator hoses at the block and shoot water in with a garden hose. You can probably tell if there is an obstruction in there. You can also try it from the coolant reservoir. You may also want to push a little water in the block while runnig and see how well the water pump is working (or not). I had the luxury of comparing mine to another 928, so I was able to determine the water pump was ok. Coolant system flush is a good idea at this time. Will probably produce better cooling anyway.

just my 2 cents
Tarek

 

You don't say how you were measuring the temp. But if you are comparing readings taken with an IR temp gun on the black rubber hose to readings taken on a bare aluminum radiator, then the differing emissivity of the two surfaces would give different readings. Some IR temp guns allow you to adjust the emissivity that is assumed when taking measurements. With cheaper units you will have to take some reference readings with a thermocouple or other contact-type instrument in order to estimate the offset.

 

Hi Tarek & Dave,
I still have an overheat problem.
Once the temp gauge gets to the 3/4 mark and above it does not come down again unless you are on a long freeway stretch. This was my first attempt to resolve it.
I have already swopped out the fan for one from my Euro and there is definitely an increase of airflow at 3500rpm over the old one. However this had no effect on the temperature.
I appreciate that the IR temp gun is not that accurate, however I was looking for an indication of where the problem may be.
The readings for the rad were all taken under the same conditions so there should be some correlation. They tend to tell me the water is cooling as it goes from the inlet to outlet.

When everything is cool in the morning I am going to check the thermostat and see if there are any problems with its operation.

 

I received a reply in my email but it's not here... [Edit]nevermind... cache flow issues...[/Edit]

Anyway, you're on the right track. Try to measure the temp on the cores and see if any of the rows seem to be running colder than others. The giveaway on mine was that the bottom 2/3 of the cores were running very cold because the flow was so restricted(Bars Leak or Alumaseal). I was getting a very small difference in temp from inlet to outlet, like 10°F or 15°F but there was a ~50°F difference between the top 1/3 of the cores and the bottom 1/3 of the cores.

The IR temp gun is best for comparing temps on the same type of material. It won't precisely measure the temp of the coolant itself like a submerged probe can, but what it can do is give you a pretty close approximation of the temp difference between two surfaces.

You may not have a cooling problem per se but you may have a system with no excess capacity for one reason or another... potential trouble down the road. BTDT.

HTH

 

Roger, I havent had any time to look at my cooling problem, but I did clean about 3 hand fulls of leaves and even a strip of bark out from in between the condenser and radiator. Still getting hot.

 

You might want to look at this...

http://www.nichols.nu/tip482.htm

 

Justin,
Trying to catch up with you on solving this problem.
I have taken out the Aux fan and started to clean out the pile of s**t between the condenser and the rad. I am then going to flush the system and rad.
Also going to blow the crud out of the fins of the rad and condenser.

Wally,
I am trying to get the 10000cs oil and will do the proceedure.
I will report on my findings.

Thanks,
Roger