Oil flow speed to cooler

UTKarmann_Ghia · 08-04-2003, 06:20 AM

Ok, as most of you are painfully aware, I am battling a heat demon. This is no ordinary demon, but a really nasty one! I'm wondering if anybody has a rough or good idea about how long it should take for my oil cooler and the return line to heat up once oil starts flowing. For example this morning I drove in to work and I usually do the cooler and oil line test to see how my oil is cooling. My oil temp was at about 215 and the ext tstat must have just opened and the line to the front was hot for a couple of feet, but the cooler was still cold as was the return line. How long should it take to heat up the return oil line?

ps - the engine comes out this Saturday to throttle my nasty heat gremlin!

lendaddy · 08-04-2003, 07:35 AM

I would think almost immediately. Sounds like you may have a restriction at the cooler. I could be wrong here but a "hot" inlet to the cooler should have a least a very warm outlet. Maybe you're getting somewhere now.

Chuck Moreland · 08-04-2003, 07:38 AM

Quote:

Originally posted by UTKarmann_Ghia
My oil temp was at about 215 and the ext tstat must have just opened and the line to the front was hot for a couple of feet, but the cooler was still cold as was the return line.

These warm first couple feet do not indicate an open thermostat.

The supply side of the thermostat is not switched, only the return side is switched. The supply side is a straight-through pipe, hence the first couple feet get warm even if the thermostat is failed closed.

This diagram shows how it works, ignore the part about the purge valve and just look at the thermostat.

To test the thermostat, always feel the lines at the cooler end. That is far engough from the thermostat to give a valid reading.

To answer your initial question, once the thermostat begins to open the return line should be warm within a minute or so.

You didn't say if the return line ever did get warm. If not, you have a bad thermostat.

lendaddy · 08-04-2003, 07:41 AM

Chuck has proven that I do indeed NOT know what I am talking about, avoid my advice like the plague!

1fastredsc · 08-04-2003, 08:08 AM

Ok, in trying to figuring out the oil system in 911's, i'm curious as to where the filter sits in that diagram? And also where the engine mounted oil cooler is since it has an on engine thermostat?

Chuck Moreland · 08-04-2003, 08:12 AM

The filter is between the thermostat and the oil tank.

The internal cooler is a completely seperate circuit driven by the pressure side of the pump. I don't have a diagram.

1fastredsc · 08-04-2003, 08:35 AM

Pressure side of the pump, now i'm a little confused. I thought the oil goind to the external thermostat was under pressure from the pump?

1fastredsc · 08-04-2003, 08:43 AM

Let me make myself a little more clear, i trying to figure out if i'm a little overly paranoid with keeping the inside of the block clean. I'm doing a top end at the moment, and i was thinking of getting some off the shelf no name oil to fill up the sump and drain a few times to get any debris out. But if it goes straight from the pump to the filter, then i don't have to worry right?

Chuck Moreland · 08-04-2003, 08:55 AM

The 911 oil pump is essentially two pumps packaged together. The pressure side feeds the engine, the scavenge side draws oil from the sump and sends it to the oil tank (through the external cooler and filter).

I wouldn't do the fill-an-flush.

1fastredsc · 08-04-2003, 09:07 AM

Hmmm, so then what would be the best approach to clean out the block a little without opening the case?

UTKarmann_Ghia · 08-04-2003, 09:08 AM

Chuck, the oil cooler indeed does get hot once it opens and both the oil lines get pretty darn hot. The return line is a bit cooler than the feed line as it should be.

So with the tstat closed, the system has high pressure and the pressure valve redirects the oil flow straight back into the tank. And when the tstat opens, hence lower pressure, the oil will flow. Doesnt the ext tstat's little windows also direct the flow?

BTW, I have a new ext tstat so it should not be a problem. Funny thing is that my temp is 215 when I stopped my car and the oil was not yet flowing. I'm assuming that the ext tstat lags the oil temp just a bit and may be an indicator that my engine cooler is indeed clogged as the temp goes up pretty darned fast till the ext catches up. This with very, very easy driving in 60 degree temps.

Here's another quick question for you Chuck: if my stock 3.0 had only the engine oil cooler (nothing else), would it overheat pretty quick or only under pretty hard driving and ambient temps?