So I was driving my 1970 Opel GT the other day and suddenly a piercing high pitched squeal came out from under the hood. It sounded like slipping belts to me so I replaced my belts and tightened up and lubed them. Unfortunately it still squealed. The sound seems to be coming from the passenger side of the engine near the thermostat, but below the carb. I removed my carb and heat shield and replaced the old gaskets and turned her back on... guess what it still squealed.
Enough backstory, here are the dynamics on the squeal:
1. It seems to not be effected by rpm.
2. When the throttle is depressed the sound gets less intense and at about half throttle it seems to disappear regardless of RPM
3. It seems to be effected by temperature, when the engine has been off for over 24hrs the squeal will not be heard upon start-up or the first about 10 minutes of driving.
4. The pitch of the squeal doesn't seem to change very much to any stimuli it just stays the same or gets quieter...
So does anybody have any idea what's happening to Mira, (my Opel) I personally think it is an intake leak at gasket to the engine.
I would go to the alternator. I thought my high pitched squeal was a bearing on alternator. But it turned out to be the fan on alternator was dragging against the alt housing. Sounds like alternator to me.
I had that high pitched whistle-like sound happen due to a vacuum leak a while back. It would rise nand fall with engine speed and disappear as the rpms went up. Like yours, it would disappear when the throttle was open because your vacuum drops to almost nothing when you hit the gas.
Try spraying some carb cleaner around the carb, intake/exhaust manifolds, and hoses while the engine is running and making the sound to isolate where it's coming from. You can also use a length of rubber as a makeshift stethascope to zero in on where the sound is coming from.
If the OP is accurate, the pitch doesn't change with RPMs, only the volume. That rules out bearings or alternator fan drag.
Pitch is dependent on a wave. A whistle isn't. Whistles retain their pitch no matter what volume they are given.
A whistle indicates an air issue. Since the engine can't really whistle with air pressure, we can safely assume it's a vacuum issue.
I know it's not the water pump, or alternator. I need to check my vacuum to the brake booster. Where does the vacuum tube connect for the brake booster? Also can a vacuum leak be loud enough to hear going 60 down the highway with the windows up and the radio on? This squeal is incredibly loud.
Thank for help so far. You guys are all very helpful.
Well, actually, when I heard you say "high pitched squeal" I immediately thought about the noise that the engine that my GTX car had when I first got it. It started making a really high pitched squeal after running for about 10 minutes. I later gave away/sold the engine and the new owner discovered nuked cam bearings. The likely scenario is that the PO who regasketed the engine hadn't primed the oil pump and no oil was getting to the head.
This seems unlikely, based on what you've said, but who knows........
Ok, it's not the brake booster vacuum line (the big line with the valve on it attached to the intake) the squeal is coming from the other side of the carburetor. My Opel also as the ARA unit on it, but no belt on it if that helps anything
Here's a link to the sound of the squeal. Opel Gt Squeal - YouTube
Please remember it does this without the belts on, so it isn't the water pump, alternator, AC, Fan, etc...
intake gasket or carb has a internal vacuum leak.[/
The intake gasket is the one between the intake and manifold right? Or are you talking about where the intake connects to the engine
take carb off and try again, if noise goes away it is somewhere in the carb, either carb gasket, or throttle bushings are leaking.
get out the 15mm box end wrench and try to torque down the intake bolts a little bit.
yes I mean where intake bolts up to engine. are you using this gaskets or rtv silicone for gaskets? I do not have much experience with using a heatshield but be careful with how good the seal is.
Also there is the T coming off intake where brake booster hose hooks up, there should also be another small tube for hooking up to the valve cover. there might also be another fitting on opposite side of intake for vacuum retard on distributor. look for any of these to be not hooked up.
these fittings are dependent on year. might all be on the T or 2 and 1. In your video at like the 7 second mark, you show the gap between carb and valve cover. the black hose you see should be going to the orifice fitting on the T, in the same frame, you can see a cutout in the heat shield, this is usually for the other vacuum line. this will be where other fitting sometimes is on the intake.
Yeah I need to give that a try. I have that gasket, I just haven't replaced it yet because I'm still trying to figure out how to remove the intake with that giant AC in the way. I use the OGTS gaskets with usually grease on them occasionally I'll use high tack gasket sealer, but I like grease better.
All my vacuum lines seem to be connected and working properly, I tested my brake booster and it passed the the test where you put your foot on the brake then turn the key.
So it's either a cracked intake manifold or a leaky carb gasket or a defect in the vacuum hose routing or a bad carb.
What on the carb could do this? How about the shaft that the butterfly rides on?
OK, not likely.
What IS likely is that the carb mating system is leaking.
You should have two gaskets and a heat shield between the carb and the intake.
It IS likely that it's leaking there.
Now, how do we know this? Easy. The whistle is on EVERY piston stroke which indicates it's connected to a central system. The only central system that makes sense is where the carb mates to the manifold.
You will be doing yourself a favor to check each of the four carb mounting nuts to see that they are snugged down. And possibly give each one a little extra tightening to see if the results change at all.
This is actually the first thing I tried. I removed the carb and heat shield and cleaned them both up really well then put on new gaskets. Put it all back together, turned the key, sqeeaaaaaaaaaaaal!!! Lol
I'll redo it again though. We aren't infallible
it is probably either this seal of the gasket or the carb has a leak. on my weber there are brass tubes coming off near the carb vacuum advance port. they have a screw in them rendering them unusable. maybe on other applications they are used for other purposes. remove the srew and they are another type of port???
maybe on yours a screw fell out, or the throttle bushings are worn, or maybe even idle jets are not turned in all the way.
carb cleaner and compressed air in the idle jets and passageway wouldnt hurt either.
A whole bunch of people over tighten the carb mounting nuts.
This can warp both the carb flange and even pull the threads up out of the intake manifold.
Get a good straight edge and check out the mounting surfaces.
im not a fan of the heat shield. if youre feeling crafty one of these days, you can reroute your fuel line around front of car, and away from heat source. electric fuel pump is a good idea for under 100 bones too. with these two mods, you can eliminate the heatshield. being in kansas maybe not. e pump fills the carb efore starting, where the heatshield is to prevent boil over of the gas in carb. making hot starts real difficult.
in your case with exhaust manifold heat riser connecting to intake its almost a must to either do the conversion to e pump or use the heat shield.
It's funny you say that that's was actually my plan this weekend was to route my fuel line in front of my radiator. I've been having some minor vapor lock on heavy acceleration
Thanks everybody for the help. It's fixed now! If anyone else ever has this problem do this.
1. Change the torque or tightness on each bolt until you find the one that makes the pitch of the squeal change.
2. Slowly tighten that bolt until the squeal goes away.(do not over tighten! The heat shield, carb and intake are all sensitive to being over tightened.)
3. Try to make the torque on all bolts as close to equal as you can.
4. Go drive for awhile! The squeal might slowly come back. If it does a very very very slight tightening or loosening of the bolts will do the trick. ( I Had to tighten).
NOTE: If you have to tighten the bolts more than just a slight adjustment, go in a star pattern like you do with lug nuts
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