AOW162435

In nearly 14 years of wrenching on many 993s for friends and local forum members, I came across something yesterday that I’ve not encountered before. I spent the day at a friend’s house, walking him through his first oil change since buying the car last year. When I removed the oil tank (thermostat housing) drain plug, I was surprised to find a typical engine case drain plug rather than the correct machined-aluminum plug.

We continued with the rest of the work, draining the case, the hard line, and replacing both filters. We’ll refill the oil once the correct plug arrives.

I’ve probably completed close to thirty 993 oil changes over the years, and I often wondered about this machined plug, and why it’s designed the way it is. A few months ago, I was at the same friend’s house in order for us to replace the timing chain cover gaskets (the car has been on stands since early 2018 as we slowly right countless wrongs inflicted upon the car by its previous owners...). Again, a job I’ve done numerous times, but in the case, we lost a great deal of oil once the chain covers were off (quarts, not teaspoons). I found it a bit odd at the time, but with what I found yesterday, I wonder if the tank/thermostat plug is designed in such a fashion to limit back-flow into the case when the engine is off?

Hopefully the question makes sense. I look forward to your thoughts.





Andreas

pp000830

I suspect the correct plug separates the oil tank contents from another aspect of the oiling system such as one of the oil return tubes or even the thermostat housing via the O-Ring. When the plug is pulled, both sources of oil are open to drain. I suspect using the wrong plug results in altering the oil flow path through the system in some way as you suspect.
Andy

k722070

if it limits or reduces back-flow does that mean it makes sense to drain the case oil with the tank drain plug removed?

AOW162435

I think you’re probably right.

I’m not quite sure what your question means. I always pull both filters and drain the tank, case, and hard line. A typical 993 oil change for me calls for 10.5 - 10.75 qts. That gives me an oil level gauge reading of around 3:00 - engine idling & hot.




Andreas

k722070

so you have both drain plugs, both filters and hard line removed all at the same time.
that was the question, my process is one at a time.
as in tank drain plug removed, drain, reinstall, then tank filter removed, drained, reinstalled.
then case drain plug, removed and so on.

geolab

Hello, The oil tank drain plug is long to be able when you remove it, to siphon all oil out when oil is cold.
It is connected to the thermostat by a cavity.
when thermostat closed, engine running, no oil passes to front radiator.
when you drain the tank engine cold, the bottom part of plug opens the cavity, and renders siphoning cold oil from front lines + radiator.

Replacing it by the short plug offsets the oil cycling to the radiator, thus longer time to reach operating temp, and hotter temps through longer usage


As for quarts of oil dripping after timing chain cover removal:
Your oil pump has 2 stages, IIRC one is 5 bar return and one 9bar main push
On the 9bar , the stage begins with the engine oil filter, and an anti-return (back-flow) inside.
any oil after this filter would be in oil passages between the filter and it's anti drawback and oil squirters , crank, lifters cams piston squirters and the famous chain tensioners..
On chain tensioners it is not squirters but oil driven small thumb like metal cyl.
I think that as soon as you touch the chains when you open the cover, the tensioner pushes back the small oil thumb on head of tensioner and lets air in the oil passages, releasing the residual oil

AOW162435

George,
Thank you - that certainly helps explain the function of the machined plug.



Andreas

nine9six

+993! Thank you for the technical content and response, George!

paulkromz