Drove about an hour or so in 80 deg temps. Fans kicked in at about 185, never reached 190 water temps. Evap system started to buzz. Figured it was not a big deal. Returned home and released the fuel pressure at the gas cap. Was surprised to hear what I believe is the fuel boiling as soon as the pressure was released. The tanks are about 5/8ths full. Currently there is NO freon in the AC system. The AC system is switched “off”. Note that the freon line runs through the gas tank in the Testarossa. QUESTIONS: 1) is there an automatic fuel tank cooling system by way of the AC? 2) any hazards that I am overlooking by running the car without freon? 2) if not, has anybody ever heard their fuel boiling? Hot fuel can’t be good!
Interesting. Liquids, in general, can boil at lower temperatures if there is a rapid pressure drop, which there may have been when you took the gas cap off. I'm just wondering if you have a problem with your tank venting system. If your AC system is not charged and the AC is not turned on, I can't imagine the pipes being hot or cold, but at ambient temperature. What car are you having problems with?
It is a 90 us spec tr. The evap system is making a vibration noise. That may indicate a faulty or sticky check valve. I have yet to investigate.... but believe it will be a relatively minor issue. As I understand it.... some cars run the ac as part of the defrost system... even when the heat is on. No doubt ferrari ran that ac line thru the tank for a reason. That makes me wonder if the ac may be running even if the switch is off. Obviously not good to run the ac without freon and oil.
Sounds like I'm out of my depth here on the TR. On most cars (Ferraris included), the AC compressor clutch is usually disabled automatically with no (freon) pressure in the lines. That's one of the functions of the pressure switch(es) mounted on the receiver-dryer. I would assume, though, that this disable system would be active irrespective of whether the system was selected on or not. There may be a heat exchanger in the tank, but it does sound unnecessarily complex adding this. I have heard of a similar system on aircraft which use fuel to cool hydraulic fluid, but aircraft fuel is usually quite frigid (at altitude). The hydraulic pumps should not be run on aircraft for long periods on the ground if fuel levels are low as the hydraulic fluid will get too hot. If your fuel level was at 5/8ths, I doubt there would be a heating issue.
My 2001 Porsche 996 has a heat exchanger for the fuel above the engine, as part of the a/c compressor. Given the small amount of fuel that is routed past the cold a/c line, right before it enters the plumbing that reaches the injectors, it has a decent chance of being effective. It is hard to imagine that one small metal pipe, running through 80 liters of fuel (or none if the level is low), far away from the injectors would be effective. I have noticed that curious pipe location on my 91 TR and thought it just an engineering solution the problem of where the place the a/c line in a mid engine car (pre 1984 engineering). I am curious, my 91 Swiss spec car has no carbon canister or evaporative controls associated with the fuel tank that I am aware of. Does a 1990 US TR? I always thought the tanks remained sealed, i.e. no vent to the outside, as removing the gas cap always led to a rush of air sound.
So then... gas starts to boil at 102 deg F (40 deg C). Still pretty hot in those tanks. The boiling could be heard as the pressure was dropped by way of the filler cap. Basic physics. The fuel is likely still the refinery’s “winter blend” with a higher RVP, lower boiling point. Need to check for a pinched vacuum hose and look into the evap check valve. Likely a sticky valve and thereby allowing too much pressure to build. These are NLA so hopefully a good soak in gasoline will help. We’ll see. If anybody knows of how the AC line in the gas tank is intended to function... please chime in.
John, This is the Testarossa system. Building pressure in the tank is normal... but with a sticky(?) check valve it may be too much. Going from a 60 deg F garage to 100+ likely adds a lot of pressure. These thin tanks must really balloon up with each heat cycle. Image Unavailable, Please Login
It appears that the line runs from the evaporator (low pressure, cool) through the fuel tank heat exchanger then up to the compressor. This uses the residual cool A/C gasses to cool the fuel a little bit when the A/C is on. CIS cars hate hot fuel, and many different makes will have a heat exchanger to cool the fuel. What you heard was the pressure from the vent / charcoal system pushing back into the fuel tank and bubbling through the fuel. Totally normal to have pressure in the tank with hot fuel. As long as it isn't a full on blast of pressure, then things are working normally. Should be some volume of air coming out the gas cap when opened, but not high pressure. Modern cars have a venting system that vents that pressure when you hit the fuel door open button, so that it doesn't blow fumes on you when you open the cap. Guaranteed that your car works fine without running the A/C, and your fuel isn't boiling. The buzz is the check valve releasing extra pressure. Check valve only maintains low pressure, anything extra buzzes right by. It will make you think there is a small animal in your garage because sometimes they squeek too.
