Dana Drury

Hi Gang,

I have one last hurdle before major maintenance is complete on my 911. (Thanks again to those who have helped me so far).

When I bought the car, she had an overheating problem, when the Porsche mechanic looked over it, he said that the External Thermostat (Pressure relief valve) was not opening up. (front trombone cooler was not getting hot)

I decided no to rebuild mine but simply replace it as there is no a 100% success rate on rebuilds.

So we put a brand new one, connected everything up and started the car, after a while I noticed that the Thermostat was leaking, quite a few drips over a 20 minute period (at the bottom it looks like the bottom sealing cap, though in hindsight it could be an oil line is letting oil drip down), the front cooler also didn't get hot, and the car got up to about 210-220 F.

The only thing was the car was on an incline, and the front cooler was raised above the thermostat.

I have checked the oil lines running to the cooler, they are slightly pressed in two areas, but not completely crushed so oil would still flow through, maybe somewhat slower.

Do these lines get blocked with gunk over the years? (I am not sure the last time that oil circulated through them)

Does anyone have any suggestions as to what might prevent the oil flowing. I suspect that the Thermostat is fine seeing as it is brand new. Is there some ways I can test or narrow down what the issue might be. I am using Mobil 1 15w50 (I believe OTTMH) which is the standard oil for our climate.

There have been no other oil leaks.

Would the car being on an incline affect the oil thermostat and the ability for the oil to circulate (i.e. would it take longer? I thought oil pressure simply forces the oil forward?)

Hopefully I am simply the jumping the gun as the car will be on flat ground when we restart it tomorrow, and it will be something as simple as the angle the car was at.

Thanks.

Jeff Curtis

The car being on an incline shouldn't be an issue, as that oil pump of yours is creating about 20-25lbs at idle, maybe a bit less...either way, once the oil heats the thermostat to it's opening requirement, away it goes!

As far as "gunk" getting in the system, clogging up the lines, YOU BET! While you had the thermostat off, you should've thought of a crafty way to flush the lines out. One way is to remove the trombone and blow some air through there, being careful to filter the opposite end through a towel or something...and verifying that ample air pressure is getting through.

The fact that your oil lines are crushed in a few spots is a concern, as that could cause areas of pressure differential and of course, coagulation of "gunk" in that area - encouraging a good clog.

Your leaks sound like you might have to reseal the lines to the thermostat a bit. They take a set when originally tightened and you will notice a ring formed on the flared end of your brass oil lines, that's where they took a set. Just loosen the fittings and give the lines a "shake" and recrank 'em...form your new "set" and the leaks should disappear. If not, you possibly have a leaky thermostat. <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />

Dana Drury

Thanks for the speedy reply. The lines, while crushed it impeeds the line about 20% if that, I do intend on replacing the line when I get the chance, I would like to make sure that the line is actually working before going to the effort of replacing the piping.

The thought to clear the lines hadn't occured to me when we put the thermostat on but I think I will look at doing that.

If the lines are clogged up, does oil eventually get through, or does it take far too long to move the oil through?

I think its the fittings that might be leaking from a quick inspection I did last night, so I will double check them.

Thanks again for the help.

Tom F

I have heard of a problem that might be your root cause. Evidently, the plastic disc on the bypass valve in the front oil cooler thermostat can come loose, and then get lodged in the oil line, blocking it. You could take apart your old thermostat to see whether this happened - you're supposed to have a special tool to undo the big slotted caps (I have one for the pressure valve plugs on the crankcase that works okay for this purpose, too), but you can make do with a vise if you don't mind leaving marks on the plugs. I think that the bigger of the two caps is for the thermostat body (interchanges with the piece in the engine thermostat, if you've got an emergency), the little one is for the overpressure bypass valve.

One more thought. I think that you can save the lines by pressurizing them with air at say 100 psi, and lightly tapping the places where they are bent. You'd have to do this with them off the car, and with something clever to block one end and pump air in the other.

Dana Drury

Thanks Tom,

I am sure once I get the lines off (considering that this is the best thing to try), I will be able to determine what might be the cause.

I spoke with Porsche centre over here in Australia and one of the mechanics said he's only ever had to repair one Thermostat that fried on a car, I am not sure how common it is (there is almost nil in the way of literature or information on the external thermostat). I will look at the lines being the possible culprit, hopefully thats the last I have to deal with as everything else that is major has been completed!

AD7TCAR

Hi, Dana. Sorry about your dificulties. We spoke a while back, as I had the same problem w/ my external t-stat. Thanks to a great thread by Thomas Sollars, I replaced the t-static piston with the valve body still on the car. I originally was going to replace the whole unit anyway, so I figured I would try to fix it with the $35 part first. I realy lucked out, as I didn't even think about clogs, and the front cooler is warming nicely and the gauge is down to around 205-210F. Because of Mississippi summers, my next project is a 99 C fan switch or a manual fan switch.
Does your oil line going up to the cooler get hot at all past the tstat? Hopefully you can find and fix the problem soon.
Someone mentioned the plastic disc on top of the relief piston possibly coming off and being a problem. I took off the botton cap, which holds the assembly in place. I thought "HUGE MISTAKE", as it was a bear to get back on, especially w/ the tstat being on the car. However, when I had it out, I noticed the screw holding the plastic disc was somewhatloose, and I tightened it up before putting it back in. The whole time I was cursing my stupid curiosity for ever taking it out, but in retrospect, I might have saved myself some of the possible trouble mentioned earlier.
Hope you get your problem resolved soon with a minimum of expense and difficulty!
Regards,
Tim

Dana Drury

Hey Tim,

Glad you got your bits sorted out, it seemed that I had two problems, my original thermostat was broken but it was actually open 24/7, so I assume that the vavle has broken off and lodged in my lines somewhere, I will be sorting it out soon hopefully.