NP993

Strange problem. Over the weekend I changed the oil -- switched, after four years, from Mobil 1 15-50 to Mobil 1 V-Twin 20-50, after reading far too many threads on ZDDP, etc.

There are three main changes, post-switch:

1. On cold startup, lots of oil gurgling noises -- never heard that before.

2. Engine seems to warm up more quickly (entirely subjective impression -- I could be wrong).

3. The thermostat definitely isn't working. The two times I've driven it since the oil change, the temps have risen past the point where the thermostat should open. Tonight, on a 45-minute drive that included a good number of red lights and traffic, the engine temp crept up close to the 9 o'clock position (this is with ambient temps in the mid-30's fahrenheit). Verified by feeling the fender that no oil was flowing to the cooler.

Otherwise, I've got perfect oil pressure, the same performance, etc. And I didn't do any other work on the car -- just the oil change. Anyone have a sense of what might be up? In all my years of working on 911's, I've never heard of a switch in oil type cause such a problem.

Mike J

I have not either. Weird.

When dumping the oil and changing filters, you followed exactly the same procedures as before? You did not fiddle with the oil thermostat, or twist anything, or had to work on something unusual?

Are you sure its not the thermostat, but the oil has different heat carrying ability, and you are seeing that? Sounds like the engine is running a bit warmer than you are used to - I thought the thermostat opens just above the 9 o'clock?

The gurgling does happen on certain brands of oil, but the one you switched is a bit thicker at low temperatures, so that might be slowing down the flow, and you are getting gurgling. Its nothing to worry about, but shows the oil flows differently.

I wonder if the engine warms up more quickly?

I am trying out an oil change of V-twin this winter - have not gotten around to it. Be interesting to compare notes.

Cheers,

MIke

axl911

Don't take chances of burning up your valve guide. The parts to change the thermostat insert is cheap and it's not to difficult. Change out your thermostat at the first hint of problem.

I happened to my 964. Thermostat went out for only short time. Oil temp gauge never got into the red. But couple months later, my oil consumption went from
1k to 400 miles per quart. Exhaust valve guide went bad.

Fix was a top end engine rebuild.

Mike J

So you are telling me that you "burned" up a valve guide but your oil temp gauge did not show the engine was running hot? Are you sure two things happened close to the same time, but are not linked?

BTE, how hot is "never in the red"? just below the red? His gauge is at normal temp.

Cheers,

Mike

axl911

I ran Mobil v-twin for a short while too and didn't notice any different behavior. But it was too expensive. I now run brad penn. Oil analysis confirmed high zddp content in BP.

In my 964, the oil temp gauge did register the high temp. It got as high as 3/4 when I noticed but could have gotten higher when it was left idling during state inspection. And I do monitor my oil usage. It went from 1k miles to 400 and smoking out the pipe at idle in a 6 months. The only thing I can attribute to was the failed thermostat.

Garth S

All the answers you need are here

Parts are ~$30 IIRC ... drain the new oil back into its containers, and fix the problem.

The specific heat value and thermal exchange properties of motor oils, dino or synthetic, are variable only with a insignificant percentage .... not enough to noticeably deflect the temp gauge [" like wow man, my royal purple cools waaaaay better than that quaker state" ] ... so the prob is not the oil.

The thermo springs fatigue over time .... rare, but the sliding block/diverter valve part can bind: bets are on the springs.

The gurgling usually indicates that the thermo is open - overheat is closed = sticking = replacement.

mcipseric

Above? I thought it opens below the 9 o'clock - at the 8 o'clock.....

axl911

It opens at the 8 o'clock. The fan (can't remember high or low speed) starts at a little bit above 9 o'clock.

mcipseric

This is true and the reason I installed the fan by-pass switch. One of the best mods for a 993!

Mike J

Yeah, but something to me still does not make sense - the claim that this caused damage to the valve guides even if the temperature gauge never went into the red.

I only hear the gurgling, when it happens, when the oil is cold - like just started. You are saying the thermostat is open then, i.e. circulating the oil to the cooler?

Cheers,

Mike

mcipseric

Yes, gurgling usaully means open....

Mike J

I am not sure how you guys know this? How do you determine that the only time the car gurgles is when the thermostat is open?

I have never experienced the gurgling when the car is warmed up, its always when its cold, and its intermittent.

You are telling me that, even if the car is cold, the thermostat is stuck open? And when the oil is hot, it does not gurgle?

Sounds a bit weird to me.

Cheers,

Mike

mcipseric

I only hear the gurgle after the temp gets just passed the 8 o'clock. I could be wrong..... have been before

axl911

This is what happenned on my 964. Oil consumption has been steady 1k mile per quart for 15k miles (2 years) since I bought the car. Took it into an inspection place and they left it idle for about 20 min while they do the checks and run the emission on the load dyno (here in texas they do load emission check). Which is fine since I want the car HOT when the emission check is done.

When I drove away notice the oil temp was above 3/4 but not into the red. Drove a while and it went down. Over next month, I noticed oil temp would go over 9 o'clock once in a while when driving (normally doesn't go over for the route I take). When it does, I notice the front fender isn't hot. Thermostat failed closed. It didn't fail and stuck close. Some days it opened, other not. So I changed the thermostat for a completely new unit and my oil temperature operated normally again.

About a month or two later, I noticed car was smoking at idle and smoke would go away when I press on the gas. Then I began noticing high oil consumption without any leak or change in driving pattern. Oil went from 1k mile per quart to 600 when I noticed high consumption. Then it went to 400 miles per quart. I was adding a quart of oil every other fill up. This is definitely different than normal behavior.

Did tear down and sent head to Ollie's. They confirmed exhaust valve guide was worn.

The oil consumption seemed to start quickly. The only change in the car or out of the ordinary event was the failed thermostat. It could have gotten into the red while idling, I don't know.

Why do we remove the engine tray? To improve cooling. When the thermostat is not working, a major component of the engine cooling is gone. Probably worse in my case since the engine was left idling. Idiling is the worst for heat build up since air is not moving over the engine or oil cooler.

For <$100 and 30 min, I would not take any chance on a failed thermostat again. On my 993, at the fist hint of sticky thermostat, I changed it.

No HTwo O

I've been running V-Twin 20W50 for the past 2 years and over 15,000 miles in my Turbo. Results have been excellent. UOA's support my selection. You will be happy with your oil, NP993. My thermostat works perfectly. It is amazing just how cool these engines run, even on hot-hot days, while on boost.

I don't hear too much gurgling, my sunroof and windows are almost always open, and the bypass pipes drowned out the rest.