Kishme79

I have a 1986 911 with 62k miles on it. I am new to the air cooled 911s. I am trying to figure out my oil consumption. I noticed that after driving the car for2 hours, the oil lines under the front fender are cold while the engine is hot. The car has over heated only twice both times the car was stuck in stop and go for 2 hours. Is this normal? Or do I need a new thermostat?

upier

Yes, that sounds like a bad thermostat. Could be fun to change. The oil lines weld themselves to the old one.

theiceman

yeah do some research on this if you are not having a shop do it . definitely sounds like the stat has failed given your symptoms.

Kishme79

Thanks everyone. Since the car generally drives at the right temp, could only the thermostat for the front cooler be failing? Sometimes the oil lines are warm and other times are cold. Makes it hard to get accurate readings on oil. I use the car a lot so I just want to mak sure I take care of her. Going from a 996 to a air cooled 911 is a learning experience.

Thanks again for all your help.

User 4221

If the front t-stat were stuck shut, one of the lines would likely be warm and the other cold.

If both lines are cold, then the t-stat on the engine is likely stuck shut.

Kishme79

I have a curious question. When I first got my 86 911, I took it for valve adj and oil change. They put Kendall gt 20w 50 which is a synthetic oil. The second time I needed an oil change the mechanic switched to brad penn semi synthetic 20w 50. My question is does it matter switching from synthetic to semi synthetic? Doe it cause any problems?

HorstP

Maybe good to know that you can change the insert of the thermostat without removing the entire thermostat from the car. Removing it can be a challenge as the steel nuts corrode with the aluminium housing and you either have to destroy the housing (big mistake) or cut the steel nuts (cheaper problem as there are repair kits such as from ER).
Not exactly sure about the comment with one line being hot, the other cold. The thermostat is in the rear right wheel well, if that is stuck, both lines will be cold.

And how you define a hot engine? Keep in mind that the thermostat to the front cooler opens at 83°C, on a colder day, it might not open at all.

Kishme79

When I am checking the lines it's after driving the car for about an hour and a half. The temp on the car temp gauge is halfway. With that said I figure the thermostat should be open. The strange thing I am also noticing is my oil pressure is a little higher. At 3000 rpm it is hitting the 5 bar and idling between 2.5.

upier

The high oil pressure seems to support the bad thermostat theory. That is one of the reasons why you don't go over 4k before the car is warm, high oil pressure before the therm opens.

HorstP

I cannot see the combination of higher oil pressure and a bad thermostat. But that is just me. Higher than normal oil temperatures would result into lower oil pressure normally. Without any doubt, if the needle is a 9 o'clock, the thermostat should be open and both oil lines should be warm/hot. Are the lines going to the thermostat hot? Is the thermostat hot itself? If you have a (cheap) infrared thermometer, you could measure both and make sure that the temperature is above 90°C.
As said, the thermostat insert itself can be exchanged fairly easily, I have done that within a few minutes and I have never done it before.

Starbuckslova1

Not an expert but still learning

Sounds like the thermostat in your oil lines is not opening
Located at right rear pass wheel well
http://www.pelicanparts.com/techarti...oil_cooler.htm

See figure 14

Check the druck press pressure

Kishme79

Oil lines to the thermostat are hot. The thermostat is warm too but could be because the area is hot from engine heat. When I touch the lines in the front passenger wheel well, the lines are cold. This all happens when the temp needle is at 9 o'clock. I have noticed the oil pressure increased when this happens as I mentioned. I am going to Check the thermostat this week. Thanks so much for all the comments. This is my first air cooled 911. My previous ones were water cooled. Thanks again everyone.

theiceman

yes ur stat is definitely toast ... or ... you have a completely crimped oil line unde the car resricting movement , this will act as a closed thermostat. check under the car where the oil lines are ( passenger side ) . A newby error is to jack under them and crush them ..

I agree with the higher temps reducing oil pressure comment ..

upier

In a given volume of gas or liquid the pressure / temperature is a constant therefore an increase in temperature will result in an increase in pressure.

theiceman

only if it is not vented system .. the oil tank is vented into the intake .. unfortuantaly some of us have found that out the hard way . The "high side" of the pump is between the pump and the bearings anyway .. the scavenge side is in the cooler , oil tank , thermostat area.