By on April 30, 2013

Mark writes:

Hello Sanjeev,

I have a problem and hope you can help me. My Cadillac Brougham with the 307 V8 smells like gas under the hood. This is intermittent and the last time it was in the shop the mechanic found no leaks under the car or around the carb.

I did some internet searching and have heard all kinds of things including I probably used the wrong kind of gas. Apparently cars like mine can’t burn premium fuel completely and there might be residual gas left in the engine. My other cars use premium so I could have pumped 91 octane by mistake. Could that be it?

If it was a leak why wouldn’t it smell all the time?

I’m frustrated to the point where chancing it is an option so let me ask you this if you can’t fix it… if it is a small leak what’s the worst that can happen? I mean doesn’t modern reformulated gasoline have such a high flash point that I needn’t worry, except for the smell? Gas smell doesn’t really bother me.

If I took a fire extinguisher around with me could I “catch” a small fire under the hood in time to avoid damaging my paint? Are there warning signs, like smoke, before flames start to actually melt things? Does fire extinguisher residue clean up pretty easily?

Many thanks,

SANJEEV answers:

Mark: I’m searching for a clever–yet benign–way to spell your name wrong, but I got nothing.  Plus, you got a machine that’s right up my Super Classy Alley, so I’ll proudly bestow my Sajeev Magic** on that sweet, sweet ‘Lac.

Old cars do stupid things because they are…wait for it…old. And you are freaking out with eleventy billion superfluous questions because of it: Fire extinguisher residue concerns?  Really???

Stay calm: it’s all good, son! Leaks happen anywhere with old rubber and gaskets, especially with today’s ethanol-blend fuel added to the mix. (Literally.) If your carb’s never been rebuilt from the ground up, now’s the time.  I betcha an internal seal is leaking, pouring fuel down the motor’s throat when it isn’t required.  Perhaps it’s when the motor is cooling down (adding space between the seal’s gaps) and when the bowl is at a certain fill level.  Or not.  But whatever the internal fail, it’s only gonna get worse from here.

I had the same problem on an older EFI car, the fuel injectors were leaking internally and the smell was horrid. You can’t see an internal leak, but you sure-as-shit can smell it. So let’s address everything. Are there any rubber fuel lines under the hood?  Replace them now, they are cheap too.  Did ya install a fancy external glass fuel filter with a removable cartridge? Throw it away and get a conventional sealed filter. Don’t know a good carburetor tech in your area?  Look harder, because now is the time.

About your Premium fuel problem, yes you are wrong for using it, but only your checking account is pissed at you. Premium fuel won’t damage an engine or leave unburned deposits above and significantly beyond a normal used motor. If you’re really concerned, you can run Seafoam in the intake and fuel system followed by an Italian Tune Up to really clean things out. After you have someone blow apart the carb and rebuild it.


**Patent pending. Or not.


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38 Comments on “Piston Slap: Fix my Bro-Ham, Sanjeev!...”

  • avatar

    “I’m frustrated to the point where chancing it is an option so let me ask you this if you can’t fix it…”

    I’m fairly certain Sanjeev isn’t coming to your house to diagnose where the smell is coming from, so you’re on your own to actually determine where it’s coming from.

    If there is no visible wetness around any of the fuel lines, carburetor or pump, you may want to take a look at the evaporative emissions components like the charcoal canister and vent lines to see if the odor is strong around them or if there is any wetness there.

  • avatar

    That Cadillac with that engine is a notorious dog 0-60 in a neck-snapping 15 seconds it was also a “leaker” gaskets leaked oil in several locations, leaky fuel pump, bad carburetor floats. The fact that it’s gone this long is amazing.

    So, Mark, if you must drive this heap carrying an fire extinguisher around with you is probably a good idea, but Don’t feel bad Mark, Yours isn’t the worst Cadillac ever built… It’s the 3rd worst The 1st and 2nd worst was your Cadillac but with the 6.0 liter 368 (V-8-6-4)or 5.7 L Diesel Feel better?

    • 0 avatar

      Hmmmm….worst Cadillac EVAH was the ’84 Cimarron with the 2.8L iron pig.

      • 0 avatar

        As the former owner of a 1987 Oldsmobile “blessed” with a 307V8 and E-QuadraJUNK carb a thought occured to me as I was reading the article a week or so ago about the soon to be released Cruze diesel. The 148 hp and 250ish lb ft of torque in the new 2.0 turbo diesel are roughly equal to the output of the old 307. This made me laugh at my teenaged self and how lucky I thought I was to have a V8.

        Why GM didn’t just put a good old SBC under the hood of those Caddies or develop a RWD version of the 4.5/4.9 I’ll never know.

        • 0 avatar

          Later Bro-Hams had the Chevy 350 (and 305?) once GM abandoned their unique-where-nobody-cares engineering hierarchy.

          • 0 avatar

            Yessir, those ones can be identified by the 5.0 Liter badges.

          • 0 avatar

            Actually Mr. Mehta, the Caddy never got the 305. 307 4brl and 350 SBC until end of “square” production in 1991 and then fuel injected 350 (later LT1) after that. The 307V8 stayed in production until 1991 just for Cadillac and the B-body wagons.

            Editing in response: Ok I was two stinking years off. So to recap kids, benefits of a 1991-1992 Cadillac Brougham (last of the good looking square body), + finally a smooth fuel injected engine, – door mounted seat belts to comply with federal passive restraint regulations.

          • 0 avatar

            Dan, per wikipedia:

            For 1991, the L02 V8 was replaced by a Chevrolet FI V8 that produced 170 hp (127 kW; 172 PS), while the Chevrolet 350 produced 185 hp (138 kW; 188 PS).


          • 0 avatar

            Principaldan had me worried about my memory for a minute. I knew I worked on a 305 SBC powered Brougham.

            From the same article:

            1987–1990: 5.0 litres (307 cu in) L02 V8, 140 hp (104 kW; 142 PS)
            1991–1992: 5.0 litres (305 cu in) Chevrolet FI V8, 170 hp (127 kW; 172 PS)
            1990–1992: 5.7 litres (350 cu in) L05/LLO FI V8, 175 to 185 hp (130 to 138 kW; 177 to 188 PS)

          • 0 avatar

            danio3834, forgive me. It is residual seething rage at the General for taking so long to add fuel injection to its small V8s when Ford did it in 1985. I enjoyed my Oldsmobile for what it was but the E-Quadrajet was a source of frustration combined with the high gearing designed for fuel economy and little else. My father purchased the car at about 50,000 miles and drove it to 100,000 miles. I drove it the next 50,000 miles before it was stolen in Detroit, MI. When my Dad started to have issues with the carb I remember telling him (at the tender age of 16 or 17) “There’s your problem. GM expects a freaking carburetor to be controlled by a computer. That’s like building an electronic butter churn.”

        • 0 avatar

          It’s all good. I kinda grew to like the Quadrabog/Quadrajunk carburetors, even the electronic ones. Even those were pretty simple once you took a few of them apart. But too I welcomed the mostly trouble-free TBI motors.

          I really just liked the Quadrajet for that awesome sound when the secondaries open under hard throttle.

      • 0 avatar

        I would say that the Cimmarron with a 4 cyl was worse…

      • 0 avatar

        No one ever thought that was a Cadillac, especially Cadillac, hence the name Cimarron by Cadillac. Says a lot about Cadillac and GM at the time. They were producing such bad cars that they distanced themselves from the product even before it went on sale

    • 0 avatar


    • 0 avatar

      Make sure the fuel pump isn’t leaking since its mounted upside down on an Oldsmobile engine.

      (yes its a Cadillac, but that 307 is a Rocket division engine)

    • 0 avatar

      A proper running 307 is quicker than that. My 1990 with 90K miles and a tuneup was in the 11-11.5 range which is still slow but not 15 seconds slow. A 307 running this slow signifies an issue or multiple issues usually involving the base timing, improperly set kick down or the carb it’self. There are tons of 307’s still running perfectly well so why is it amazing that this one is till going. These are 300K mile engines with proper care and I have seen dozens with this many miles that still purr like a kitten. Leaking valve covers and the odd fuel pump should be the main culprits and of course the oil sending unit up by the oil filler which is notorious for dribbling oil.
      The 8-6-4 is hardly the worst Cadillac as it was essentially the tried and true cast iron Caddy V8 tied to the tough THM 400 transmission. Cutting a single wire disables the 8-6-4 leaving you with a smooth running reliable V8. The title of worst goes to the diesel and HT4100 disaster.

    • 0 avatar

      Can’t be worse than the V6 4.1 (252 ci) offered in the ’81&’82s. What a wretched lump that was.

  • avatar

    Sanjeev, glad you mentioned the issue of “today’s ethanol-blend fuel”. Living/working in the Iowa/Missouri/Kansas area means its very difficult to avoid purchasing ethanol mix (Iowa does offer no ethanol fuel, but its generally 5-10% more expensive. The other states you have to go looking for specific stations that have no ethanol base). My ’08 Astra is the rare non flex-fuel GM and runs horrid mileage on the ethanol mix v. regular petrol; 23-24 mpg to 28-29 mpg. I also noticed it ran through spark plugs like a meth-head with a disability check. I hadn’t thought of the possible damage its done to my ’95 Cobra, though I always put premium in the 302 V8. Good advice to stay away from it unless you have no other choice with an older vehicle.

    • 0 avatar

      I live next state and find it impossible to find non-ethanol gas. My car has a lot trouble with it. I’ve started adding a booster to each tank. The improvement has been dramatic

  • avatar

    It never ceases to amaze me the misconceptions people have about “premium” fuel. BTW, I have a TR6 with 3 Strombergs and consider a portable fire extinguisher between the seats as cheap insurance. I’ve never had to use it, but ya never know…..

  • avatar

    I seems to recall that a few years ago an awesome commenter wrote in a Piston Slap question about E10’s effect on his sweet Dodge Diplomat.

  • avatar

    I remember back in my youth, my friend and I did some engine mods on my ’79 Mustang Pace Car. Put on full length headers and dual exhaust, and an Edelbrock intake and Holley double-pumper. We got it all put together and started the engine with the hood up to look for problems. We set the timing, and it was idling nice and smooth. Then I noticed some liquid boiling off one of the headers. What’s this rubber line pressed tight against the hot exhaust header tube? Why, it’s our hack-tastic fuel line setup. The fuel line had slowly charred from the header heat, and after 20 minutes or so had developed a small leak. It was boiling gas! I ran to shut off the engine, and my buddy ran to get a fire extinguisher. Luckily it didn’t catch fire.

  • avatar

    The quadrajet carb would sometimes develop a leak on the inside. There were a couple of plugs that would no longer seal for the metering rods, and you can get a gasket that fits under them to fix the problem. At least you used to be able to, I haven’t looked recently. But the leaks were often intermittent.

  • avatar

    This post makes me want to find a clean Brougham, Fleetwood Brougham or Brougham d’Elegance and LS-swap it.

    These cars ARE Cadillac. Nothing reaches this level of Broughmgasm.

  • avatar
    Kyree S. Williams

    You could do as Lincoln does and spell his name “MK”. That’d do it…

  • avatar

    I learned, among other things–from 7 years spent as a 911 operator and fire/police dispatcher–that cars and trucks burn up way more often than you might think.

    I carry a fire bottle in each of my vehicles, and none of them are as old as the one in question (though my Panther is getting there) nor reek of gasoline. I personally know two people that lost cars to the infamous Ford “cruise control flambe.”

  • avatar

    I have a basic question about premium fuel, if a cars owner manual suggests to use premium should I go with it?

    I’ve been pumping premium into my Volvo 240 and it seemed to help the acceleration and fuel consumption, but using 89 rated fuel has pretty much the same effect (and is the minimum suggested by the manual).

    • 0 avatar

      If you haven’t found a difference between 89 and 91, and 89 is the minimum recommended, you’ll be fine using 89.

      In the case of my car, the manufacturer recommends 89 to get advertised power. I’ve tried 89 and 87 and haven’t noticed an impact to fuel economy. I haven’t taken it to the track on both to make any performance measurements.

  • avatar

    I had this same issue on a 97 Chrysler LHS (I know, fuel injected vs carb’d but hear me out). Intermittent fuel smell that was strong when it would occur. I thought it could be the evap can as well so I replaced it as I had a spare. Nothing.. Same problem. So it got the point that I decided to get under the car and start yanking on the vent hoses that ran underneath the car. There were no leaks so I knew it had to be a vent. Wouldn’t ya know. There was a disconnected vent hose that went from rubber to plastic. It had dried out and you could not quite see it as it was routed inside a rear frame assembly.

    I found out that the hose was actually a connector hose between a plastic and rubber hose. Replaced it and no more smell. HTH..

  • avatar

    Late to the party, but I have to take slight exception to the “premium is cool for everyone” concept.

    My Fiancee’s Scion TC hates premium during cold startup. Since high octane fuel is harder to light (which is the point), when it’s just cold and humid enough, the motor doesn’t want to light the mix and will stumble until it gets some revs together.

    Putting the 87 the owner’s manual wants (it IS just a camry motor, after all), solves the problem.

    It might just be her car, but the result is the result. If the computer and the engine can’t take advantage of the high octane gas, there’s no real reason to use it.

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