F-Body Europe

Two weeks ago I found a sudden overheating of my Firebirds 3.4l V6 engine during a hot summer day (cruising within the city, no hot run). Till this day the engine run normal, even at high temperature. Two days later I noticed a remarkable coolant loss of about 2,5 l and added coolant as described in the owners manual (cold engine!). Morning of the next day i checked coolant again and again added 0,5 l missing, started the engine and it run normal. Now, coolant temperature was normal. Till this time everything seemed fine. During run the engine lost power for a while - heavy shaking of the engine at idle - then run again normal at normal speed. This happened for some days as I noticed coolant loss again and again. The engine again lost 0,5 l on a short trip (only few km) !!!

I let my workshop check the engine: compression is normal, no oil mixed with coolant or vice versa, but they also noticed: sometimes it smells like coolant while idling (e.g. waiting on a traffic light). No water found under the car, no wet hoses, nothing. The workshop even checked for leaks at high pressure - nothing.

What could cause this sudden heavy coolant loss ?

Classic signs of a blown head gasket.

Ditto!

If we would ignore this fact (broken head gasket), what else could cause such a sudden and horrible loss of coolant?

I cannot imagine a blown head gasket.

1. The rough idle occurred AFTER I refilled coolant. It is not very frequently, sometimes and at ANY temperature. I.e. if stopping the engine with this fault, this still occurs next day, when starting the engine from cold. We found out, that if it is running rough, it is running too fat, after a certain time it runs normal again, regardless of temperature...

2. From my experience a damaged cylinder head (hair crack) or blown gasket (whatever gasket) would either show up permanently, or at some temperature range (like my Audi 15 years ago which had a blown intake manifold gasket, which stopped regularly on the highway while the engine reached a certain temperature).

More interesting: what came first egg or chicken? Till I noticed the coolant leak, the engine was running without any problem. After I filled it with coolant it still looses coolant and now does not run anymore. I noticed a similar problem with a VW machine years ago. However, this machine had air bubbles in the engine after refill. I had to fill coolant over days until the engine was running again without problems - hot spots on the cylinder walls while the engine wasn't cooled evenly.

Broken water pump ? Perhaps, you wouldn't notice this if it is broken a few days before, and had not time to corrode... How to check ?

Any other ideas - except blown cylinder heads/gasket ?

Or: how to check, for blown gasket ? Oil and coolant are not mixing each other, so the chance would be good to find out leaks from the outside, isn't it ?

BTW: how to explain water inside the passenger area (both sides coming from the center of the front console) while it is not raining ? Not a joke, but a problem since years.

Since your coolant does not drip/leak outside, it must leak inside.
If your gasket leak between the oil galley and the waterjacket, you will have oily water or watery oil (not in your case).
If your gasket leak between the water jacket and the combustion chamber, then the water will disappear as vapor (sounds like your case).
However, first check the thermostat. If it's stuck then the engine will overheat and boil the water off as steam (but you should be able to see a temperature rise on your gage).
Waterpumps usually don't break, they just start to leak at the seal. You should be able to see it weeping.

I am no expert on American engines, but is there a way that the water can get anywhere near the intake ports (leaking manifold gasket)? That way the engine will suck water at idle (high port vacuum) and maybe cause the coolant smell as well. This way your compression also show up as normal, since the head gasket is intact.

Just wondering: could it be that one of your heater hoses or the heater core inside the car is leaking? That way you get water inside the car (and the smell).

Thank you for your comment.

We are just checking, whether the heater (heater and A/C located under the front console inside) is leaking.

I'm not an expert too, but having some experience with broken gaskets and/or refilling problems ...

However it seems that the 3.4l V6 doesn't have problems with air bubbles in the block (cite from my workshop master). So maybe we can exclude this problem.

A faulty sensor might be a good new starting point. However: since I refilled the system, the temperature was achieved to be normal and stable even if running at 100 km/h on the highway (short distance) - no problems on the first day after refill procedure.

Maybe there are some people, who know the 3.4l engine (BTW: built 1994) a little bit more in detail to give more input. We - my workshop master as a consultant and me, knowing all the problems of this car - are mouse trapped. His first explanation was to have found a blown cylinder gasket, too. As I explained all problems in detail - there seems to be a little chance not to must have opened an engine which was running before.

Strange anyway.

Any ideas, stupid or not, are welcome !

I'm gonna stick with 2 slow on this and say check your heater core. Once you get that fixed . P
ut a radiator test cap on the radiator and see if you are over pressurizing the system. Also you should be able to purchase some test strips to test for coolant residue in your exhaust. But a good sign that something is wrong is steam vapor coming out the auspuff.

2slow and Roy, this forum I missed for years. Great! Thank you for your input til now. Right, I will give feedback on our results from the heater core inside the A/C. Keep the line for me, as your ideas are good.

Roy, as far as I know the workshop already tested over-pressurizing the system and also tested for water in the exhaust system, as you indicated. With no result.

The only thing we know for sure: the block is still blowing air in the coolant recovery tank from time to time. The filling level in the heater core of the engine drops from time to time (at the same time?). Maybe, not a real sign of a leak - as I experienced with my former VW Passat. And, maybe, coolant smell comes from the burps from the engine. You'll never know, til you experienced it.

I wont give up on this item, since I completely rebuilt the passengers area a few days before the desaster begun: 2-color gray leather on the original seats, new carpets, replaced center console arms (which seems to be one of the most faulty constructions of these cars, cause it breaks while you keep your eyes to close on it)...

Maybe I'm wrong, as they already checked this. As the ECT sensor (coolant temperature for the ECU) of this engine is located on top of the engine, this may explain anything or nothing. Maybe even a faulty sensor due to overheating. Thus, overheating the block, caused by the ECT sensor yielding wrong temperature. Remember: we detected sudden, temporary rough idling, which may cause temporarily overheating while running too fat. In contrast, the coolant flow is expected to react rather slowly on short time-scale variations in temperature - if filled correctly.

However, the temperature readings from the gauge does not vary and is within its limit, now. Is it obtained from a different sensor with the 3.4l V6? Not sure, as having to carefully read Chiltons manual by myself.

What is the expected total coolant volume of the 3.4l V6 block? Don't know, as having to completely drain/refill the coolant (cannot do this, as the car is in the workshop, and I'm in my office).

So,
What else may cause a temporarily rough/fat idle at any temperature, causing the block to temporarily overheat this way, which perhaps may cause overheated (hot) coolant gases blown into the recovery tank?

Up to now, we only can say: all clarities are eliminated...

I once had a faulty coolant temp sensor and the car refused to start when it was hot or idled really rough. Once also the connector broke off and i got a SES light and the PCM went into dummy-mode (fans on etc), so the sensor near the thermostat housing is in fact the once for the PCM (and also for the gauges, as far as i know the 3.4 has just this one, i at least didn´t find another one).

The entire coolant amount in the 3.4 should be around 11l, if i remember right (i´ll check that).
And if you still have that red DexCool coolant in your car (smells a bit like $hit), flush your system very very good before refilling it with normal green coolant (if you want to use that) as mixing both is pretty dangerous - but there are for sure people here that can tell you more about that

Not giving up and 500 Euros later (a lot less compared to rebuild the complete engine):

Got my car back after several meetings, phone conferences and/or looking into a irritated face of my workshop master. Seems, it is running again. Say it again and again: never open/change a running block since it is not really neccessary.



They checked the complete engine. Everthing is working fine - except one cylinder shows a worn spark plug. Obviously a little problem of the valve mechanics (oil). But, this problem is well known since three years and the car does not consume more than 1l of oil per year or 15.000 km. Again: if it needs no repair, don't open.



Thanks a lot. THE information missing here. We have flushed the complete coolant system one year ago, but did it with my workshop. At least, from that time, the car is not using red DexCool or similar. The only reddish liquids which I remember are transmission oil, rust protection paintings and lacquer.

As I suggested, I didn't seem to refill the coolant correctly. There were additional 2-2,5 l of coolant missing.

The good news: we now know about (1) a faulty idle stepper motor, sometimes causing problems by wrong air mass flow when you start/stop the engine, (2) the heater/air condition is not leaking - any knowledge is a success, even if you pay for looking at a component, which needs no repair -, (3) the engine seems to be in a normal to good condition compared with the kilometers which it run (170.000).

Anyway, it is a very good idea to check the coolant level on a daily base within the next weeks... One never knows.

That is so true, and I believe the phrase you are looking for goes something like this: "If it ain't broke, don't fix it!"

Exactly. My german/english dictionary was lost somewhere between the tools while I rebuilt the interior of my car. And there are only a few screws which I don't find anymore. But, try to find anything while having cables around your neck, paint on your shoes, rust protection under your nails and your customers are wondering that you do anything else than using keyboards to fix their IT problems...

Thank you all for your hints and mental support.