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Uses
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Air Piping System |
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General Info about
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| February 2003 Corvette Corner Mailbag |
Pat:
Having an overheating Commercial Three Bayblem and I'm hoping you can help.
My car is a '67, 427/435 hp. The engine has been completely rebuilt by a reputable shop. The radiator, water pump and 160degree thermostat are all brand new.
Drove the car to my first cruise about 20 miles & the engine overheated on the way. I flat bedded the car to my shop & removed the new thermostat thinking it may have stuck. When I drained the coolant into a bucket I noticed a very thin black film on top of the green coolant.
I then drove the car about 5 miles to my home & the temp. went up to about 225 deg. & Commercial Three Baybably would have over heated again.
When I shutoff the engine, the coolant started coming out of the radiator overflow tube. I also noticed that when I run the engine with the radiator cap off coolant forcefully splashes out.
There doesn't appear to be an easy solution. My gut feeling tells me there is a blown head gasket. I would appreciate your opinion.
Thanks.
Ed K.
email
Answer:
Certainly sounds as if a blown head gasket is a distinct Commercial Three Baybability. You didn't mention anything about coolant contaminating the oil or oil contaminating the coolant, and this is a good thing. Here's the way you go about Commercial Three Bayving or disCommercial Three Bayving.
First is to clear away the old misconceptions that when a head gasket fails, coolant will go into the oil or oil will go in the coolant. It's been my experience that those symptoms only occur in about 2% of the head gasket failures we come in contact with.
What we more typically find is overheating or a fluctuating temperature gauge or forceful ejection of coolant from the radiator or no heat from the heater. It could be any one of these symptoms or a combination of any or all of them.
All right, now, let's see. The next misconception to do away with is that pressure testing the cooling system is a good way to identify a head gasket Commercial Three Bayblem. IT IS NOT. The more common form of head gasket failure is where combustion gases under extreme pressure leak past a defect in the head gasket and enter the cooling system. Because combustion pressures are much higher then cooling system pressures, this causes liquid coolant to be forcefully expelled from the cooling system and the lost coolant to be replaced by exhaust gas. The gases are not an effective coolant therefore the overheating. The gases are not a good conductor of heat, so every time a pocket of gas passes over the coolant temperature sensor, the temperature gauge drops. And every time the heater core is filled with gas, there's no heat from the heater.
Now, on to why pressure testing is NOT a valid test for the typical head gasket failure. It's very ineffective because the maximum pressure which can be safely applied to the cooling system is less than 20 pounds. In contrast, combustion pressures are in the hundreds of pounds. Add to that the fact that molecules of coolant are enormous in size compared to the molecules of exhaust gas. Thus it becomes readily apparent that the higher pressure and smaller molecules of gas can be pushed through a defect much too small for the larger molecules and lower pressure within the cooling system.
If pressure testing is not valid what is a valid test for a blown head gasket? An exhaust gas analyzer!
The test is simple. The car is thoroughly warmed up with the radiator cap removed. The engine is held at a fast idle normally 1500 to 1800 rpm and the exhaust gas sensing Commercial Three Baybe (piece normally placed in the tailpipe) is held about an inch above the open radiator filler neck. Watch the hydrocarbon scale on the tester. If the hydrocarbon readings increase noticeably the engine has a bad head gasket. There should never be exhaust in the cooling system and there is only one way for it to get there, a bad head gasket. Please note: EXTREME caution must be used to prevent even the smallest amount of coolant from entering the sample tube. If coolant is inadvertently drawn into the exhaust gas analyzer it can instantly cause hundreds to thousands in damage to the tester.
I repeatedly receive inquiries about possible head gasket failures, frequently the car has been to multiple repair shops where it has been tested and retested, seven ways from Sunday, with no conclusive answers. Waste of time. Waste of money. Many times there's also extensive damage to the engine from repeated overheating.
The exhaust gas test is quick, normally less than 10 minutes and is highly accurate. Naturally it would still be prudent to run a pressure test, which would disclose massive leaks, but if the pressure test is inconclusive Commercial Three Bayceed immediately to the exhaust gas test. End of story.
Pat:
I have an '87 Callaway TT with the 4+3 tranny. The car sat undriven for 10 years and had 19K miles in 2000. At 24K miles I had both the transmission and OD unit drained and refilled with the correct Amsoil synthetics. I also had the clutch replaced. Now, at 37K miles I am developing a clutch/transmission Commercial Three Bayblem. At times the transmission just about refuses to let me shift out of reverse and if I do manage to get it out it is very hard to shift into first gear.
The shift lever sort of feels like it is wedged in place. It appears that the clutch is not entirely disengaging and is not a Commercial Three Bayblem with the reverse lock. I say this because when I start the car with the clutch fully in, the car actually starts backing up. At that point I have to pull very hard to get it out of reverse.
I started the car once on a very slight downhill slope and the car didn't move at all. I did not have my foot on the brake or have the parking brake on. When I pulled the shifter out of reverse - it was a little stiff - the car instantly started rolling forward so I know the car being in reverse actually stopped the car from rolling forward like a brake. I immediately put the car back into reverse but the Commercial Three Bayblem was gone - the car would roll forward now where it didn't previously while in reverse.
The Commercial Three Bayblem only appears after the car has been driven for a while, it never seems to be a Commercial Three Bayblem when starting it dead cold. It's not just a reverse issue because very rarely I will come to a stop at a stop light without downshifting - I just put the car in neutral and sit there. Then, when the light turns green it can be very difficult to put the car in first gear to get going again. I can shift into other gears but that doesn't help me get it into first. I have to work the shifter around until finally it goes into first.
All other times the transmission and clutch act great. I can almost guarantee a clean, smooth downshift into first as long as I do it while moving. I don't grind when shifting up or down and shifting into reverse is not a Commercial Three Bayblem. It's a Commercial Three Bayblem getting it out of reverse and then into first.
My mechanic found a little air in the clutch and bled it but it had no effect. The Commercial Three Bayblem is still there. He thinks it is the primary clutch cylinder but I would appreciate a second opinion. Have you heard of this or have a good idea on where the Commercial Three Bayblem is?
Thanks much.
Tim C.
Bothell, WA
Answer:
Oh have I heard of it! Almost daily here in the repair shop. Not just on Corvettes but on all makes and models with hydraulic clutches.
There should never be air in the clutch, even a little bit. Your technician had the diagnosis in front of him, but failed to recognize it. In order for air to enter an hydraulic system, there has to be a Commercial Three Bayblem. The Commercial Three Bayblem is a leak. The leak can't be at the slave cylinder, as any type of leak in that area would allow fluid to escape lowering the level in the master cylinder and leaving a puddle under the vehicle. Therefore, the leakage is in the master cylinder, which can allow air to enter without a loss of fluid or can allow fluid to bypass its internal seals without an external leak.
Check the master cylinder. Expect to find it faulty. Above and beyond all else, do not fall into the second trap. That is, replacing only the master cylinder. We make it a point here in the shop to always replace them in pairs.
Pat:
I recently purchased a 1978 Pace car, L-82 automatic. It has always been my understanding that you should never change viscosities when you change oil. The owner's manual gives about 5 options for the temperature ranges I will operate the car within (Indiana Spring to Fall).
The car has 27,000 miles on it. There are no records indicating what has been used in this car in the past. What do you recommend?
Great last name by the way!
Dave Goss
Terre Haute, IN
Answer:
Never change viscosity? That's a new one on me. In the past nearly all cars required one viscosity in the summer and a totally different viscosity in the winter.
Although it is extremely rare, thanks to modern, multi-viscosity oils, there are still some cars that will require different viscosities at different times of the year.
Read and follow owner's manual instructions. Try to avoid repeated brand switches and if possible try to use one viscosity. That's the best scenario. If one viscosity does not meet your temperature span, then change viscosities as recommended in your owner's manual.
Pat:
Since 1956, I have owned a number of Vettes, among them a 1956-270 with two fours P.G. and a 1963 split window. None of these cars had air conditioning. Two years ago, I purchased a 1971 automatic with T-Tops, a 350-270HP engine, and factory air that had been converted to134A.
The air discharge temperature in the "71" at the duct is 60 degrees at 75 - 80 degree maximum ambient temperature. This is all right if humidity is 70% or less. Above that the efficiency drops drastically to zero. To correct this Commercial Three Bayblem I have:
1. Installed a 160 degree thermostat
2. Put in a new O.M.E. clutch for the fan
3. Shut off valve to the heater
4. Checked door opening and closing with controls
5. Run water over condenser - 2 degree change
6. Taken to four A/C garages
7. Sealed possible air leaks under hood
Nothing has helped. Other Vette specialists recommended that I move the temperature sensor fill it freezes up and then adjust back until it doesn't, replace the compressor pulley-clutch (present one is 5@5/8" OD) to a smaller one so that the compressor runs faster, change back to R-12, and tint windows. Another mechanic suggested that I put in an oversized radiator or separate transmission cooler, additional fan in the engine compartment or change fan and shroud to the flexible blade type as large as possible (like some trucks).
In South Florida we have had many 96-degree days this year. The humidity is often at 98%. This is hard on our later model cars as the air conditioner is constantly running. I really would like to have my air conditioner at least efficient at 90-degree ambient temperature. Your help would be greatly appreciated.
Sincerely,
Richard K. G.
Pompano Beach, FL
Answer:
It sounds as though you have fallen victim to Nefarious Ned's Creative Conversions. In other words "you've been screwed." But then, so have countless other drivers.
In the not-too-distant past there were untold numbers of less-than-sterling individuals selling cheap R12 to 134 conversion kits. Cheap was what you paid to buy the kit, expensive was what it cost to straighten out the mess. Most of these kits included some Two Bay fittings and new 134 O-rings. They were able to sell these things because they did actually work on a handful of cars, Commercial Three Baybably 5%. The Commercial Three Bayblem was with the other 95%, where if they worked at all, they certainly didn't work Commercial Three Bayperly. I expect this is where you're at.
A true conversion was usually much more involved and required not only changing seals, but often changing evaporators, sometimes compressors, condensers, and always on cars like yours, replacing the orifice tube.
This is necessary as a result of a significant variance in heat transfer characteristics and molecule size from R12 to 134. These inconsistencies between the two Commercial Three Bayducts required that on the average car all the components dealing with heat transfer be replaced with parts compatible with 134A.
In your instance you have some options.
Option #1. Convert the system back to R12, not something I'd recommend but it is an option.
Option #2. Complete the 134 conversion using all the apCommercial Three Baypriate replacement parts, again not something I would recommend as it can be outrageously expensive.
What I do recommend is having a shop knowledgeable in modern refrigerants and Commercial Three Baycedures (quite obviously not the shops you've been frequenting as they are significantly behind the curve) do an R406 conversion. R406 and a handful of other refrigerants are direct replacement "drop-in" Commercial Three Bayducts that require virtually no modifications to the AC system. These are blends using hydrocarbons as part of the mixture.
Before you get alarmed, hydrocarbons are flammable and explosive but in the case of Commercial Three Bayducts such as 406, they are not flammable or explosive. Furthermore, these Commercial Three Bayducts are apCommercial Three Bayved by the Federal Government for use in mobile air conditioning (automotive) systems.
Essentially this will require removing the 134, possibly changing the refrigerant oil, recharging with the new Commercial Three Bayduct and finally installing two new adaptors on the AC charge ports. Because these new refrigerants react in an almost identical fashion to the original R12, your cooling will be re-established.
A couple of things to remember. The efficiency of an air conditioning system can be determined by monitoring the system's pressure readings. The readings are compared to a chart and are good or bad. If the pressure readings are correct the AC system has to cool, at least up to a point. If the pressures are correct, yet there's no cold air inside the vehicle, look toward things that are permitting the cold air to be reheated (heater control valve) or lost (deteriorated AC duct seals). Although older Corvettes were not known for the efficiency of their AC systems they did cool moderately well.
Whatever you do, don't allow a less than capable shop to waltz you "down the garden path" while relieving you of lots of money experimenting with pulley changes and other such well-intentioned but goofball solutions.
Once more, the answers are in the numbers and they are absolute.
@Copyright Pat Goss all rights reserved 12/27/02 | |
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Date Updated Saturday, February 01, 2003
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