Cool Trombone / Oil lines means bad thermostat?

[grahamkissack]

Just noticed after a 20 minute drive tonight (55F outside) that my oil lines to the trombine cooler were still cold even though the engine reached temperature of about 200F according to the gauge picture below. I thought the thermostat should open at about 180F?? Perhaps a stuck thermostat? I presume I should try a longer drive at hotter temps before resigning myself to the nasty thermostat removal job? Thoughts?

[James Brown]

Why does everybody believe the gage? wait till it's good and hot outside and I bet they will get good and hot. Check the oil temp at the oil tank and cross reference the gage to see if there close. oil temp is not sensed at the oil tank but should be close if everything is well warmed up. And get a real gage in there. Pelican sells one with real numbers on it and comes with a new sender and it looks great also.
The thermostat on the engine opens (at 180˚F) to send hot oil to the internal cooler then to the engine then to the oil temp sender then the oil is scavenged to the oil tank. If the scavenged oil is too hot, the aux oil cooler thermostat opens and sends oil to the front oil cooler. So yeah the oil has to be quite hot to open the AUX thermostat.

[ShakinJoe]

Pelican has been out of stock on this item for quite some time!!

[grahamkissack]

Originally Posted by James Brown

Why does everybody believe the gage? wait till it's good and hot outside and I bet they will get good and hot. Check the oil temp at the oil tank and cross reference the gage to see if there close. oil temp is not sensed at the oil tank but should be close if everything is well warmed up. And get a real gage in there. Pelican sells one with real numbers on it and comes with a new sender and it looks great also.
The thermostat on the engine opens (at 180˚F) to send hot oil to the internal cooler then to the engine then to the oil temp sender then the oil is scavenged to the oil tank. If the scavenged oil is too hot, the aux oil cooler thermostat opens and sends oil to the front oil cooler. So yeah the oil has to be quite hot to open the AUX thermostat.

Thanks James...I'll drive it under hotter conditions and test the actual tank temperatures to see if the gauge is in the ball park. If the internal thermstat opens at 180F, what does the external one open at or is it the same at 180F?

[James Brown]

ShakinJoe, That's to bad, that is a great mod. Maybe Palo Alto Spedo will have some.
Grahamkissack, I'm not sure but it is around the same temp. But it is located way downstream and takes longer to open, if at all. Most of the time the engine cooler works good.

[Sunroof]

Look in the rear right wheel well............do you have that big multiported thermostat? Well, the internal mechanism will go bad and the device will simply not operate. If your pipes are not hot leading from the thermostat to the cooler up front, its simply not working! Oil is not flowing to the front cooler...........I have the same issue on my 1973.5T..........

Several threads are around that address the removal, repair and replacement of this unit. Its a bear to take off because of the lack of space for good leverage. You'll need fitted oil line wrenches. The coupling(s) between the unit and hoses usually go bad (strip) trying to get the damn things off and several will need replacement. They are $45+ each and up. If you can manage to get the unit off you may consider taking it to a shop where they can replace the internals.

My mechanic said, he would gladly "heat" the unit and loosen the fittings enough for me to remove it and make the exchange. Keep that strategy in mind. Heating and getting leverage on it with a breaker bar is probably the trick to removing it. Should not be expensive for the shop to do it. Since the housing is pretty strong, replacing the internal pieces might be the cheaper way to go. The complete OEM thermostat unit can be had from $350.00 up from what I have researched. I have seen aftermarket units much cheaper. Keeping oil temps in range is critical in 911's.........at an interim measure I installed Heet Sheets and the Cooler Collar to hold my temps down a bit while I get going on the external thermostat repair.

Good luck and keep us informed

Bob

[dad911]

I'll wager you are not getting it hot enough to open the thermostat fully. Also keep in mind temp sender is measured at the engine, not at the thermostat.

[rbuswell]

Originally Posted by dad911

I'll wager you are not getting it hot enough to open the thermostat fully. Also keep in mind temp sender is measured at the engine, not at the thermostat.

A twenty minute drive doesn't seem that long to get all that oil warmed up enough to open the thermostat. They are very well made parts however and don't fail that often from what I've heard. The factory didn't do a good job of anti-seizing the nipples however and the aluminum shreds even with heat ... ask me how I know!

[Gogar]

If you want to easily and cheaply make sure your gauge/sender is working properly, you can buy a $10 digital meat thermeter and CAREFULLY place the probe into the oil tank, in a way you know you can get it out.

[86 911 Targa]

Originally Posted by grahamkissack

Just noticed after a 20 minute drive tonight (55F outside) that my oil lines to the trombine cooler were still cold even though the engine reached temperature of about 200F according to the gauge picture below. I thought the thermostat should open at about 180F?? Perhaps a stuck thermostat? I presume I should try a longer drive at hotter temps before resigning myself to the nasty thermostat removal job? Thoughts?

Keep in mind that the front cooler thermostat is not an on/off device, but opens gradually starting at about 185F.

As others have stated, take the car out for a longer drive.

Also, the oil is always at the cooler input, and circulates back to the engine when the thermostat starts to open.

So long as you can reference a numerical value v/s red & White oil temp by the gauge/needle position, you should be ok with that gauge assuming it is accurate.

Godd luck,

Gerry

[boyt911sc]

Originally Posted by James Brown

Why does everybody believe the gage? wait till it's good and hot outside and I bet they will get good and hot. Check the oil temp at the oil tank and cross reference the gage to see if there close. oil temp is not sensed at the oil tank but should be close if everything is well warmed up. And get a real gage in there. Pelican sells one with real numbers on it and comes with a new sender and it looks great also.
The thermostat on the engine opens (at 180˚F) to send hot oil to the internal cooler then to the engine then to the oil temp sender then the oil is scavenged to the oil tank. If the scavenged oil is too hot, the aux oil cooler thermostat opens and sends oil to the front oil cooler. So yeah the oil has to be quite hot to open the AUX thermostat.

James,

The auxiliary thermostat line to the auxiliary cooler is always open (permanently open). It is the return line that is being controlled by the auxiliary thermostat. In short, the auxiliary cooler is filled with oil as soon as the warm oil from engine goes to the oil tank via auxiliary thermostat. The warm oil from the engine keeps circulating back to the tank until the oil temperature reaches 180°F plus.

At this temperature (180°F +), the return oil to the tank (from engine) is gradually reduced and at the same time, the oil from the cooler is allowed to flow back to the tank. The cross-sectional area of the opening (for cooler's return line) and closing (oil engine return) are kept the same or equal to prevent pressure build up. At any given engine oil temperature, the combined % valve opening and closing are equal to 100%.

Tony

[James Brown]

Well operating on the front side or the back side, the results are the same. Thanks for the info.

[burgermeister]

I recently tested 2 used & 1 new regulator in a pan of water. The 2 used ones had the plunger slightly raised proud of the piston when cold, and started extending at 180-ish degF. The extended plunger was very stiff. (hush in the peanut gallery).

The newer regulator had the plunger somewhat recessed inside the piston when cold, and took about 200 degF to extend. The extended plunger was a bit spongy. (I said hush).

I had both types in my car. The used ones opened around 190 degrees, the new one barely got the lines warm at 210 degrees.

I measured oil temps with a cheapie IR thermometer at the line into the thermostat.

Lesson: If you plan on replacing your thermostat regulator, test the new part first! Or do the job twice ...