ONAFLYER

Car is running great, learning how to drive it having fun during first session. Mid-way through the second session it just dies, sorta, down the front straight at over 110 in fourth. Granted it is very hot, mid 90's, check the gauges and coolant looks good but oil light is flashing. I think the car went into a limp mode, struggle around the turn and pull off. After a minute it restarts and seems fine then, goes right back to limp mode, pull off again and now I have a split hose spewing all over. after being towed in, it cools off a little and I repair the hose with some miracle tape with hope of getting it home. After about 5 miles it dies again, and I call AAA. Again. I dont even know where to start, could it be a faulty sensor shutting off the car? I'm wondering if the coolant sensor or oil sensor gone bad would put the car into "limp" mode? It seems to run fine after cooling off when I left the track. Now it starts and dies. No CEL either. Any help would be great. Thanks, Drew

Lots of flakes in filter housing, Not Good.

Macster

It is possible if the oil temp too high (but the level is still reasonable) the DME will put the engine in limp mode.

I have read that in this case the DME limits rpms and in fact will disable fuel and spark to the various cylinders in turn to limit temp build up.

In fact, I've either read from somewhere official or been told that it is possible to drive the car sans any coolant but I've no confirmation on this and I'm not recommending anyone try it and I'm certainly not going to try it and even when had a couple of chances to try it I elected to pull over to the side of the road and wait for the tow truck. In both cases facing a long long tow (in one case over 600 miles...you don't want to know what this tow cost.)

Killing the engine I'm not so sure about. There's a risk in if the decision to kill the engine is wrong this could be a safety issue which I don't think Porsche would want to assume. IOWs, Porsche leaves it up to the driver if he wants to continue to run the engine after the warning lights indicate severe engine damage is imminent that is the driver's decision. Maybe the loss of an engine at this time is the lesser of two evils...

Anyhow, the symptom reads like the crankshaft position sensor is acting up. If this acts up the DME has no idea where the pistons are and therefore can't know when to turn on the injectors or when to trigger spark so it does neither. Result: Engine dies, or if this happens at engine start the engine cranks but does not fire. Since emissions are unaffected the check engine light probably won't light up, though there may be a Porsche specific error code logged somewhere that is retrievable by the use of the proper Porsche diagnostics computer.

And it could be the MAF or even a fuel supply or pressure problem. You can disconnect the MAF at the wiring harness and see if the symptom returns.

To eliminate fuel supply and pressure causes obviously the fuel supply and fuel pressure have to be measured.

But first, fix the cooling system leak and properly, and a properly means that tape of any kind is not involved. Be sure you get all the air out of the system and this is not easy without the proper equipment.

Sincerely,

Macster.

ONAFLYER

Thanks for your input. I need to check for codes, and of course replace the hose. I followed the Bentley manual on how to bleed the air out. Maybe it was not all the way, hard to tell. I drove it hard before I went to the track, and survived 1 1/2 sessions before it let go. Whats your thoughts on the low-temp thermo now available?
Also, I had the fuel pump replaced in December. And a new clutch, flywheel, RMS and LN IMS just for peace of mind, all at 130k miles. Now at 137k.

Macster

Basically I'm against low temp t-stats. I know these are all the rage, but I think it is a solution looking for a problem, and as a cure may be worse than the disease.

I have some info that lists wear vs. temp and the info is that at low temps (IIRC 170F: I do not have my references handy) the wear over 70 hours of running at this constant temp was much higher than the same test done with the temp 10F higher.

As the test temp was raised -- and more engines tested for 70 hours -- the wear continued to drop until at 210F the wear was at its lowest.

This testing was done at the temp listed thus we are not talking about wear due to low temp starting but wear arising from running at a constant though lower than 'normal' temp.

So, I'd be leery of going to a low temp t-stat without clear signs this was needed and what those signs are I'm not sure. My 02 Boxster's coolant temp has reached 226F (more than once) and stayed there for in at least one case hours when driving in extremely hot amibient temp. And the last time when monitoring the coolant temp when it reached 226F I pulled the car over and let the engine idle and even at idle, with probably less than 2 bar oil pressure, the engine suffered not one whit from this extreme heat.

In your car's case, given the engine has accumulated 137K miles under some track usage with the existing T-stat with apparently no signs of any problems I can't see there's a problem with whatever coolant temp the engine's experiencing. If there were I think you'd know it by now, it would be evident from the way the engine ran.

Sincerely,

Macster.

ONAFLYER

I tend to agree with you on the low temp thermostat, maybe if it was track only car. It was changed last month when I replaced the coolant tank and all the engine hoses after my first track experience went bad with this car.

I just plugged in a scan tool, shows P0300, random misfire. So I cleared it and no change, as in it wont start and run. Battery seems to be weak now too, I'll put it on a charger and try again.

Thanks for all your input, I've read many of your posts and learned a great deal. You are a valued asset on here.

Macster

Glad I was of some help and your comments prove you are too kind.

However, you might want to change that smiley to a frownie after this though...

If the car was a track only car you'd still be I think wrong to change to a low temp t-stat. Why?

Well, say you're running 5w-40 oil. That '40' is the viscosity of the oil at 212F. If the oil temp is lower than that because of the low temp t-stat then the oil is thicker and this presents more drag. That's costing you hp. And the wear numbers I posted didn't say they applied to street usage only.

If the oil temp is too low wear occurs no matter what. You could wear out your race only car's engine quicker, and finish lower down in the standings too.

You do not want to run the coolant cooler just because you can. You want to run the coolant cooler because the engine shows it needs this or because the engine runs better because of it.

Before I'd mess with the coolant temp I'd consider adding more oil capacity (deeper sump but it needs to have proper baffling) and an Accusump to ensure the engine never starves for oil. To win you have to finish and you can't finish if the engine spills its guts out on the track due to oiling problems.

Still love me?

Sincerely,

Macster.

ONAFLYER

I've spoken with EBS racing about an improved baffle system for the M96 engine, hopefully its not to late for my engine.
After changing the battery, and cleaning the throttle body and air tube, the car started right up. Then it started to rattle, coming from what sounded like the top of the engine. I looked around for something obvious to no avail. Does a AOS going bad make any noise from your experience? I sure hope its not internal damage...

insite

macster -

i have to respectfully disagree about the low temp thermostat. i USED to think it was a gimmick, because once the car is at operating temperature, the OEM 190 thermostat is more or less 100% open in all but the coldest climates. the aftermarket 160 would be 100% open as well, making these two parts equivalent.

then i realized something: the thermostat location on the boxster is REVERSED from the usual position on most cars. it is at the engine INLET rather than the engine OUTLET. this means that rather than trying to maintain the water temp in the motor at 190, it's actually trying to maintain the cool incoming radiator water at 190. it also means that as it opens, it allows cool water past it, which will then close it again......

as i understand it, the reason behind this is to reduce thermal shock to the motor. this opening / closing of the t-stat as cool radiator water enters the engine will more slowly equalize the radiator & engine water temps. in the usual design, the thermostat will open wide until the cooler radiator water has completely filled the engine. THEN it starts to close again, starting the cycle over. the hot/cold/hot/cold cycle as temperatures equalize is supposedly not good for the engine. corvettes use a similar system ot the boxster.

the problem with our cars, though, is that lack of convection can allow some hot spot to form inside the motor. convection is a powerful heat transfer mode; without it, the engine internals don't get rid of heat nearly so quickly as when the coolant is moving full force. THEORETICALLY, this can affect the metal matrix composite cylinder liners, and could POSSIBLY be a root cause for the d-chunk failures.

in all but the coldest temperatures, the low temp thermostat allows full flow in more conditions than the OEM t-stat. for a track car in particular, this is important. the critical condition for d-chunk would THEORETICALLY be when the temp guage shows the car is warm, but the t-stat is not really open.....and then you start to HAMMER the car w/ high revs. stagnant water around the cylinder liners reduces heat transfer rates; hot spots form & the liner cracks......the low temp t-stat reduces the likelyhood of this happening IMO.

once the car is really warm, the low temp t-stat is not maintaining the engine at a lower temperature than the OEM, so oil temps would be about the same. the difference is in that critical period of time where the temps are up, but the OEM t-stat isn't really open yet.....

sjfehr

AOS failures have a few different symptoms, some of them audible, but I don't think a rattle is one of them. When my AOS failed, the engine made a godawful screeching/whining noise; it wounded like I thought a bearing seized and the serpentine belt was slipping, but was actually the intake pulling a vacuum on the block through the failed AOS, and air leaking past the crankcase seals.

Macster

If the coolant is above the t-stat's open temp the t-stat is open. The t-stat's job is to restrict coolant flow and reroute coolant from the engine back into the engine to warm the engine up to operating temperature as quick as possible.

Even so I have observed it can take some driving time at moderate speeds/engine loads to get the engine up to 'temp'. I say 'temp' because the temperature at which the coolant stabilizes depends upon other things least of all the t-stat.

I took my Boxster out the other day on a warm (mid 80s to low 90s) day and drove the car really hard in the mountains up a grade with lots of high rpms at relatively low speeds.

I can't post the entire PDF of data -- if you ask via PM I can reply with the text file of the data file size is 91KB -- but even with rpms reaching 7139 the coolant temp never got above 215F. (Intake air temp ranged from 102F to 95F.)

Might add the highest speed the vehicle obtained during all this was 69mph and only for a second or two. The grade was steep enough and the road curvey enough the bulk of the time the transmission was in 2nd or 3rd gear.

When I pulled over to the side of the road and let the engine idle at 30:08 into the trip. The coolant temp continued to climb (engine at idle mind you) until 30:28 into the trip it reached 222F. This I think highlights the importance of a cooldown lap before coming off the track and even letting the engine idle a few minutes afterwards.

Anyhow, at 30:28 into the trip the coolant temp had climbed to 222F. The engine was still at idle. Oh, the A/C was off the whole time (I sacrifice for my data).

At 32:05 into the trip the coolant temp had dropped to 212F. The radiator fans were still on (they do not shut off until the coolant temp drops to 205F.

I got tired of sitting in the heat so I took off again.

Almost immediately I was on the freeway and the vehicle moving at speed (70mph to 75mph).

Rpms were around 4K (under a bit and over a bit). Intake air temp was 102F.

Let's see....75mph was obtained at 33:32 in the trip.

I continued to drive at 75mph and the coolant temp continued to drop. At 33:47 into the trip the coolant temp dropped to 204F. By my observation I know the radiator fans shut off at 205F. As I continued to drive the coolant temp continued to drop reaching 203F at 36:31 into the trip.

But by then I was off the freeway and on surface streets and driving at 16mph when the temp reached 203F.

Surface road driving then found the temp climbing again. At 37:07 the temp had climbed to 208F. At 37:27 the car was at a stop and the engine idling (700 +/-).

At 37:32 the temp climbed to 210F, the at 37:42 to 212F. The fans come on (low speed) at 212F. Still with the car at a standstill and the engine idling the coolant climbed to 215F at 37:53 into the trip and remained there until 38:39 at which point it had come down to 212F.

Then at 38:54 the coolant dropped to 210F and I shut off the engine at 39:18 and the coolant was still at 210F. The intake air temp at this point was 111F.

I fail to see how installing a colder T-stat would have helped any. The bad old factory stock t-stat was wide open at those temps.

If you want to improve your car's cooling at the track or anywhere do what Porsche does. Install more radiator capacity (add a 3rd/center radiator) or modify the radiator fans to come on a lower temp or to come on and remain on all the time.

My Turbo has both a 3rd/center radiator and the radiator fans run all the time (which is a characteristic of the Turbo stock setup) and runs a heck of a lot cooler than the Boxster.

And with no need to install a colder T-stat and thus no risk to thermal shocking the engine or in any other way interfering with its behavior off the track.

Sincerely,

Macster.

insite

i agree that the colder t-stat does nothing once the entire cooling system is up to temp. it only makes a difference during the transitional period where the engine coolant is hot but the rest of the system isn't quite there yet.

ONAFLYER

lots of flakes, Not good.

TrackDays247.com

Oh no. These poor cars seem to have more than a few things that now MUST be done prior to advanced track running...

Hope it works out.

budmanv24

Looks like my oil filter housing. I haven't had a chance to dig into mine yet. Will be curious to see what you discover.

ONAFLYER

looks like you already have a 3.4 engine, according to your bio, is that engine the one with problems? I plan on doing that or more if my crankshaft is OK, unless I can find a deal on a GT3 engine. I'm going to do some serious research on making this thing more "bulletproof" if possible...