"it overheats, but only when stationary." Check the radiator fans *NM*

So about 6 months ago, had a blinking temp light. Found out was low on coolant. Topped off, and away it went.

Yesterday, wife is driving car and calls and says that temp light was blinking, and oil light was turning on and off.

I pickup the car, and the temp is slowly climbing, and finally gets into the red. So I pull over, allow the car to cool, add 1 gallon of water, and drive another 10 minutes
before it overheats, but only when stationary. The oil light also comes on, but mainly when sitting, not driving.

Allow to cool again, add more water, and drive the rest of the way home.

Today, start the car, and runs perfectly. I was thinking failed water pump, but removed the access cover, and it sounds fine. No signs of coolant anywhere.
So I then think maybe cracked expansion tank. Same thing, no signs of coolant underneath rear trunk carpet.

Now, apparently the temp sender has failed because the temp gauge no longer operates, but still blinks. I let it run up to temperature in my garage, and cannot find
any leaks whatsoever.

Perhaps the thermostat was not working?? But where is the coolant going??

any ideas?
much appreciated

This is so common, I am quite annoyed that Porsche hasn't just demanded thicker plastic from their suppliers.

In the rear trunk, pull the carpet/liner around the coolant tank (right side). If it is leaking, you will have some fluid under there.

If it is, get it fixed right away as the system is under pressure and could get worse, like all of a sudden, and you will then pay for a flat bed.

Peace
Bruce in Philly

Quote
chamilun
So about 6 months ago, had a blinking temp light. Found out was low on coolant. Topped off, and away it went.

Yesterday, wife is driving car and calls and says that temp light was blinking, and oil light was turning on and off.

I pickup the car, and the temp is slowly climbing, and finally gets into the red. So I pull over, allow the car to cool, add 1 gallon of water, and drive another 10 minutes
before it overheats, but only when stationary. The oil light also comes on, but mainly when sitting, not driving.

Allow to cool again, add more water, and drive the rest of the way home.

Today, start the car, and runs perfectly. I was thinking failed water pump, but removed the access cover, and it sounds fine. No signs of coolant anywhere.
So I then think maybe cracked expansion tank. Same thing, no signs of coolant underneath rear trunk carpet.

Now, apparently the temp sender has failed because the temp gauge no longer operates, but still blinks. I let it run up to temperature in my garage, and cannot find
any leaks whatsoever.

Perhaps the thermostat was not working?? But where is the coolant going??

any ideas?
much appreciated

split. The coolant gushes out with some violence and once pressure is relieved the tank split closes up. Since the cooling system is now low on coolant the pressure will not build. I have driven a car, my Boxster, a couple of miles from cold with a split tank -- topped up with water first -- without any signs of a coolant leak even though the day before when hot and under pressure the hot coolant gushed out like an upside down Old Faithful geyser.

What I would usually advise is with the cooling system topped up and with no air pockets (which in your car's case it likely has now) to run the engine, drive the car, get the system nice and warm (hot) to the point the radiator fans come on. Then you shut off the engine and as the heat makes it way from the engine into the coolant the pressure rises and this is about the best pressure test there is since the system is not only under pressure but it is hot. In this context the tank is about as pliable as it can be and if it has a split/crack it will leak.

It also gives you a chance to ensure both fans come on when the coolant gets hot enough. (A fan was not working in my Boxster's case but this did not cause the tank to split. 200K+ miles of use did that. In fact I had a radiator fan quit in my 996 and yet the coolant gage didn't even show any signs of any cooling problems, there's that much margin in these cooling systems.

But with your car's cooling system compromised a hot pressure test is going to be some work to do right and doing it wrong can lead you to form the wrong conclusions.

You or a tech is going to have to get your or his hands dirty.

Start with getting the car in the air and inspecting the bottom of the tank as best you can. Feel for any signs of a crack/split and likely some dried coolant residue. However if the tank is split and a lot of coolant flowed through this the area might be washed clean of this residue. Push against the tank to see if you can compress/depress one side of the split. You are looking for asymmetrical response of the tank housing to pressure from the outside.

Unless you can spot sufficient signs the tank is indeed leaking, a cold pressure test is at least called for and my hope is the tank it bad enough it will leak. But it may not. Thus you might have to have the tech pull a vacuum in the cooling system and refill the system and then do the hot pressure test.

It is unlikely the water pump or t-stat is bad. 'course you can't test these without running the engine and as it heats up ensuring the coolant hoses leading from the engine to the radiators get warm as the t-stat opens and the coolant then flows.

You can with the belt removed check the water pump for any play or abnormal feel when rotated that might suggest the impeller is damaged. You can also inspect the water pump for any signs of leaking coolant. My info is the pump seal can seep a tiny amount of coolant but there should never be any wet coolant visible and even the size of the dried coolant residue stain that can be present on the pump housing should be small, but how small the techs would not tell me.

Remove the plastic plate by the filler and it is visible just below the filler. I belive it has an o-ring in it, and the o-ring can go bad.

wow.
thanks for all the help guys. Ill update once I try the culprit.

(interesting comment about the expansion tank heating & cooling allowing for leaks to occur at different times. )

A slightly low coolant level generally won't cause overheating unless air gets sucked into the system, which only happens if the reservoir is quite low. If that's the case, the problem will generally persist until you bleed out the air. Driving with the bleeder valve open for a while should do the trick.

One thing to check (since it's easy) is the ballast resistors. Instructions here: [pedrosboard.com]

You can also check under the water pump for signs of leakage, which is normal as it starts to fail. The water pump is located on the bottom of the car behind the passenger seat (for left-drive cars). If it's leaking you should see white crusty stuff on the bottom.

Those really are the top three.

For completeness you should also check the last two digits of your coolant cap (443.121.321.XX) to see if it's one of the obsolete designs. I think the latest version is 04.



Edited 1 time(s). Last edit at 04/21/2013 10:37AM by Boxsterra. (view changes)

... I have seen three cases where a faulty ignition switch won't run the radiators.
Make sure they are running (with the A/C off and the car to full temp).
If they don't run check the ballast resistors and the ignition switch.
Happy Bocstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

all fans are operating correctly. I thought about getting a pressure tester over the weekend from HF and see what happens, but Im gonna take a more simple approach.
run the car to temperature, then slide a paper towel under the expansion tank. if it gets soaked after the cool-down process, I think that should confirm what I believe to be
the problem: expansion tank.

right now the door is also apart from failed regulator #2 in the last two years...joy

... oil with the dipstick.
If it's chocolate milkshake then you know where the coolant is ending up.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

thanks Pedro!

Update

took a close look at the expansion tank, and noticed right away it wasn't terribly yellowed like many of the failures Ive seen posted online. The rear deck was dry also...
Stuck a paper towel under it and ran for a while, and found no dampness whatsover. At this point, Im thinking the worst ie failed head gasket, but was puzzled as didn't see any signs
in the coolant tank or with the dipstick.
So, thinking back, I remember there being dampness on the roof over the tank area after my wife pulled over saying the temp gauge was rising.

After hearing so many stories of failed caps, I took a look at mine and sure enough, it ended with -01, one of the older designs. Picked up a new one from the dealership that
ends in -04, replaced, and everything seems good to go. I also changed the coolant temp sensor as my gauge wasn't working (or at least I thought it wasn't).

After filling with coolant and following bleed procedures, and still getting no reading on the temp gauge, I found a post that mentions theirs did the same thing after over-heating, but reset after about 15 minutes of driving. So, took her for a spin, and voila, no more blinking light, temp is correct again.

So I think I've got this one solved. Thank to everyone for their help.