I think I’ve mentioned before how I’m continually astounded at how there’s always something new to learn in this vast universe of automobiles. I’m a painful car geek, one that makes people fling their drinks into plants at parties just to get the hell away from me before I pin them into a corner and start talking about turn signals, and even I find things I had no idea existed all the time. Like just recently when The Bishop sent me a link to this Facebook Marketplace ad for a 1982 Datsun 310GX, and told me to look at the picture of the engine bay.
I’ve mostly forgotten about these old Datsuns, but I remember liking them in a pretty mild way back in the day. They were appealing in a sort of quiet way, similar to other transverse FWD economy cars of the era, but with somewhat different proportions, and I don’t remember these being quite as common as VW Rabbits or Dodge Omnis or Toyota Corollas.
Also, they had some cool coupé variants with great bubble-glass rear windows:
But we’re not here to talk about the exterior design, the weirdness is under the hood! So look at this:
Do you see it? It’s weird. Here, let me show you:
There it is; that fan. A little fan in the engine bay, not anywhere near the radiator or any part of the HVAC system, but still clearly a factory-installed part.
And it’s not just on this car! You can find videos and pictures of other people “discovering” these fans (you know, Columbus-type “discovery” of something that was already there) and also wondering what the hell they were for:
They are quite a little puzzle! They look like little desk fans with their wire anti-finger-chop cages. Here’s another video of some fan-discoverers:
So what are these fans? They appear to be pointing at the carburetor, nestled there under the big air cleaner drum. But why?
These carb-cooling fans aren’t unique to Datsun 310s, but they’re close. Doing a bit of digging with the help of The Bishop, I’ve only been able to find two other cars that have carb fans: the Fiat X1/9 and the 40 and 60 series Toyota Land Cruisers.
So, again, what was going on here? Why did these cars feel the need to blow air on their carbs, unlike pretty much every other car ever? The answer is, of course, the only true answer to any confounding question: sometimes, things just kind of suck.
In fact, our old pal Murilee Martin made mention of this very fan and its purpose while exploring a junkyard a few years back, and his assessment is the correct one. These fans exist because carbs, fundamentally, kind of suck.
I mean, they’re amazing machines, strangely complex little analog computers that deal in fluids and air and vapors, creating miasmas and admixtures like little clockwork alchemists, but they were also vulnerable to all kinds of trouble from such vast and untamable factors like weather and ambient heat and atmospheric conditions.
One of these big issues was vapor lock, where the fuel, largely due to excess heat, would become vaporized before it got to the carb, creating all kinds of fuel delivery problems and making your car stall, frustratingly. This was especially common for cars with inline engines that positioned the carb or carbs right above the piping-hot exhaust manifold.
My old Volvo 1800S was like that, and would often drip fuel from its twin SU carbs right onto the exhaust manifold, where it would smoke and sizzle in a nicely terrifying manner. And, yes, sometimes I would get vapor lock.
So these little fans were an attempt to mitigate the national scourge of vapor lock, by attempting to cool that carb down so the fuel wouldn’t be trying to come in as some ghostly cloud. If you don’t believe me about how much vapor lock once held America in its cruel, wispy grasp, maybe you’ll believe an animated version of former New York Jets quarterback Joe Namath:
See? Now who’s laughing? Not Broadway Joe, that’s for damn sure. He gets it.
As did, it seems, Fiat, Toyota, and Datsun, at least on some select models.
Vapor lock really hasn’t been a major issue for decades, as the problem was pretty well eliminated with the widespread adoption of fuel injection. Still, it’s interesting to see what sorts of somewhat desperate-seeming measures were used to combat the inherent sloppiness of old carbureted fuel systems, and again, I’m sort of amazed this is the first time I’ve encountered this particularly quaint solution.
Can any of you impressive car geeks think of another car that used carb fans? I wouldn’t be surprised if there are more!
Huh, my brat loved every bit of heat the lake of gas in the intake manifold could achieve.
My 71 Vega used to vapor lock on the hottest Hudson Valley summer days. Never while running, always on restart. Popping open the hood for a few minutes always fixed it and allowed bystanders a chance to admire the awesome Vega powerplant while I waited.
It certainly is! I’m a big (1.91meter) fan of my two Dellorto DRLAs, especially when they sing in tune when performing 😉
So about 20 minutes a year?
-Running and ducking
Though seriously, a good set of carbs, pre-emissions, properly tuned are a glorious thing. Horrid for the environment, but FI can never seem to quite match the throttle response. Well, modern FI probably CAN, but not with modern emissions requirements, and ye olde FI definitely could not.
That is quite clever! Wish I’d had one of those on my first car!
“…as the problem was pretty well eliminated with the widespread adoption of fuel injection.”
As well as moving catalytic converters underneath the car rather than keeping them under the hood where their excess heat caused vapor lock – Something which rarely occurred before the mid-70s in water-cooled cars.
Modern cats are literally built into the exhaust manifolds of many cars today. Doesn’t get more underhood than that. The closer they are to the cylinders, the quicker they light off and the quicker the FI can go into closed-loop operation. Also why so many cars today idle rather high at startup for 15-20 seconds – to get the cats working.
Vapor lock was common well before the 70’s.
“become vaporized in the intake manifold before it got to the carb”
gas tank->intake manifold->carb->cylinder????
All my old cars were
gas tank->carb-> intake manifold->cylinder
I was just going to ask the same question…
Yeah, if you have liquid in your intake manifold, I’d be more worried about hydrolocking.
Does the fan just run when the car is on, or is it also on a shutdown timer so it runs a few minutes after the car is shut down? My experience with vapor lock is that it prevented restart more than caused a problem during driving.
Well this wasn’t to prevent vapor lock, it was to prevent percolation and since that most commonly happens after the vehicle is turned off yes they have a system to make them run after the vehicle is shut off.
Why not run a fuel return line back to the tank and let circulating fuel cool the carb.
The fuel rails on a Chevy 350 TPI are always cold when the engine is hot, because it’s circulating fuel back to the tank.
Many carb cars used a return line to prevent vapor lock.
My Corvair (and EVERYBODY ELSE’S Corvair) used to love to vapor lock all the time. Would have enjoyed a little fan pointed at the fuel pump.
What about that giant fan right above the entire engine?
It was nowhere near the fuel pump. And it was nowhere near the carbs for that matter.
My 1988 Nissan 300zx Turbo had fuel injection but also a fan and ducting to blow air over the injector rail in the middle of the engines V, To prevent vapour lock, The car would struggle to start when hot without it. The fan would come on if the engine reched a certain temp and was then switched off.
My friend had a 1981 280 ZX with a similar fan set up.
At the other temperature end are all the contraptions used to keep the carb from icing in cold temperatures. Ducting and dampers to direct intake air across the exhaust manifold, running heater coolant through the intake manifold, etc.
Ah yes, “the many ways gasoline will try to kill you”, a core ground school topic. (Admittedly, carb icing isn’t exactly gasoline’s fault, just inherent in carb design.)
Not sure if they still do it, but, coolant through the throttle body was big with GM in the ’90s and ’00s, so that wasn’t just a carburetor thing.
Ford too. But that’s more of a “don’t freeze open” kinda thing for literal freezing conditions.
Some vehicles were equipped with non-feedback carburetors for this very reason,depending on the manufacturer.
Especially for vehicles in colder climates.
Not just carbs, many fuel injected cars have thermostats in the airbox to direct outside or exhaust heated air to the intake. And heated throttle bodies are common too. An FI throttle body can ice up just the same as a carb.
Yes, My Skyline has coolant going through the throttle body to help with the temperature, My VW T3 has an electric heater under the carb and can draw warm air from the exhaust area and my T2 runs a small exhaust pipe through the inlet manifold. Until your comment I hadn’t realised how different all 3 of my cars where in this regard. 🙂
Perhaps you find some more references on a Fans Only site.
A clothes pin clamped on the gas line to turn the vapor back into a liquid was the solution my father taught me.
Generally, you need a lot more than one…
I was like “I was a carb fan once…my bike has one, as I thought it’d be fun to once in my life own something carbureted. But I no longer think that b/c yeah…” Damn misleading headline – this is no support group!
Haha I was going to make a comment along the lines of “wait are there no longer carb fans out there anymore? Because you will get a lot of the drag racing people that prefer them”
The majority of my bikes are carb’d, one Suzuki and one Buell even use the same model. The Buell XB still needs assembly and the Zero needs no petroleum at all.
I prefer carbs because I too am old and weird.
Stuff like this is why I’ll never make fun of anyone falling for the old blinker fluid gag. Is blinker fluid or muffler bearings really that absurd sounding compared to really things like carburetor fans or diesel exhaust fluid?
The new unlimited wireless ads kinda suck. Hope you are being compensated handsomely.
Riding in the back of the family truckster (Mid 70s industrial spec Suburban) in the mid-eighties, headed from the upper midwest to California, we were crossing the liminal space that is Nebraska in 110º heat, and the car started bucking and wouldn’t run properly. My dad figured it was vapor lock so would stop and use ice from the cooler to help things get going again.
The next day the issues continued as we climed through the Rockies after Denver. Often slowing us down to under 30mph on the freeway. By the time we started heading down the back side the trusty Suburban seemed to be on its last legs. When my dad conseeded defeat and pulled into a service station the mechanic let him know it was a failing fuel pump. All the hours letting things cool hadn’t helped the vapor lock but it had let the fuel pump cool down enough to gain a little more life.
Before I even clicked on the link, I thought “probably to keep the fuel cool”
Looks like I was right! banishing the scourge of vapour lock.
I mean if it works, cheap and easy fix.
I had an old Audi with the turbo inline-5 and mechanical fuel injection. It had a fan that blew air onto the fuel injectors to mitigate vapor lock. So it’s not uniquely a carburetor problem.
I think its more a low pressure forward mounted pump issue than a carb issue. I don’t think its an issue as much with higher pressures or with rear mounted electric pumps, all even more mitigated by adding recirculation.
This is it. Vapor lock occurs when a bubble of fuel vapor forms in the fuel line between the fuel tank and BEFORE a fuel pump mounted near or on the engine. The pump sucks fuel through the line from a distant tank with very low pressure before forcing it into the carb. So the fuel line must remain cool and that’s probably what the fans do. Here’s another bizarre carb thing: bolting a carb directly to the intake manifold of some engines can subject them to sufficient vibration to foam the gas in the float bowl, interfering with it’s being drawn into the venturi. One solution is to fasten the carb to the manifold using Thackery washers, very strong flat washer-like springs which when MOSTLY tightened hold the carb in place but dampen the transmision of high frequency vibration (https://usa.minisport.com/wbb9990031000-thackery-washer-for-webber-dcoe-each.html).
And not just for carbureted cars either, the Z31 300ZX, at least, had a cooling fan for the injectors. It was on a timer and would run for 5 minutes or so after the car was shut off. I remember being confused for quite a while by that when I had my first one, not knowing what it was that continued to run after the car was off.
WEBER 4 LYFE
Excuse me, I need to clean my idle jets…
The car didn’t have a fan built in, but my dad kept cardboard in the back of his BMW 2002 for me or my brother to use when the car decided to vapor lock (which was annoyingly often).
Until recently I had no idea there were fans of tail lights.
Welcome to the Autopian. We’re happy you’re here. 🙂
Oh just you wait till the conversation turns to Jatco Xtronic CVTs!
I remember friends with good cars complaining about vapor lock in my youth. But the pieces of crap we drove never generated enough power, thus enough heat, to create such issues.
Crap old cars are often more likely to have it because it’s much more common on non-crossflow engines, such as under the bonnet of most British cars before the 1980s. It’s quite possible to get vapor lock with less than 50hp.
Thus adding insult to injury.
Willing to let them slide on this, does it even get warm enough in the UK to induce vapo(u)r lock?
60 degrees and light drizzle is all you need!
On the 70’s/80s Mini, not only is the intake/carb and exhaust crammed between between the engine and the firewall, the fuel pump and fuel line from pump to carb are all nestled in there too.