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Old 04-17-2016, 02:04 PM   #1
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Default Heater Core Bypass

So yesterday, I finally decided to give my couch a rest, and get the 93 Park Avenue back in service that was parked for a leaking heater core.

I was first made aware of this hose in my internet searches:

Gates 18743
More Information for GATES 18743
Quote:
Centerline Length (in) 9.8
Centerline Length (mm) 249
Inside Diameter 1 (in) .62
Inside Diameter 1 (mm) 16
Inside Diameter 2 (in) .75
Inside Diameter 2 (mm) 19
Number of Branches 0
Alternate/OEM Part Number(*): 10743, SID8743

Used in:
CHEVROLET BERETTA 1992-1994
CHEVROLET CAVALIER 1991-1994
CHEVROLET CORSICA 1992-1994
FORD ESCORT 1984-1987
FORD TEMPO 1984-1985
MAZDA 929 1992-1995
MERCURY LYNX 1984-1987
MERCURY TOPAZ 1984-1986
PONTIAC SUNBIRD 1991
VOLKSWAGEN JETTA 1981-1982
VOLKSWAGEN RABBIT 1980-1982
VOLKSWAGEN RABBIT CONVERTIBLE 1980-1982
VOLKSWAGEN SCIROCCO 1981-1982
I figured I could make it work by flaring the small end and working it on.

Then I went down to AutoZone, and discovered this part while looking at their hose rack, which was a whole $2 cheaper even:

Dayco 70553
Quote:

Color Black
Contains Heat Shield N
Contains Protective Sleeve N
End 1 Inside Diameter (in) 3/4
End 2 Inside Diameter (in) 7/8
Hose Type Dual I.D. Hose
Material EPDM
SAE Specification SAE J20R4 Class D-1, SAE J1684 Type EC
Trunk Height (in) 6 3/4

Used in:
AMERICAN MOTORS AMBASSADOR 1967-1974
AMERICAN MOTORS AMERICAN 1967-1968
AMERICAN MOTORS AMX 1968-1979
AMERICAN MOTORS CONCORD 1978-1979
AMERICAN MOTORS GREMLIN 1972-1976
AMERICAN MOTORS HORNET 1970-1977
AMERICAN MOTORS JAVELIN 1968-1974
AMERICAN MOTORS MARLIN 1967
AMERICAN MOTORS MATADOR 1971-1978
AMERICAN MOTORS PACER 1978-1979
AMERICAN MOTORS RAMBLER 1969
AMERICAN MOTORS REBEL 1967-1970
AMERICAN MOTORS SPIRIT 1979
JEEP CHEROKEE 1974-1983
JEEP CJ5 1972-1981
JEEP CJ6 1972-1975
JEEP CJ7 1976-1981
JEEP GRAND WAGONEER 1984-1991
JEEP J-2500 1972-1973
JEEP J-2600 1972-1973
JEEP J10 1974-1988
JEEP J20 1974-1988
JEEP JEEPSTER 1972
JEEP WAGONEER 1972-1983
The 7/8" end appears to be simply the last inch of a 3/4" sized hose that has been flared out and made bigger.

I chopped the flare off, making that side a little shorter than the other, and simply put it between the two heater pipes. It worked out perfectly, because the two heater pipes in this application are offset a bit anyway. Hoseclamps, refill, air bleed, done. I chose to leave the heater hoses attached to the heater core, mainly so I don't lose them, because they are so hard to get replacements for in this application. They stay at the firewall, and are not in any danger of getting caught up in anything.

I believe this should work for any C/H body L27. I couldn't find this information anywhere on the internets, so I am sharing it now so that it may help others in the future. I don't know if this info will span to other engines (LN3, L36, or L67), but if it does, please feel free to throw your two cents in on it.

I do know, however, that the W-body L27 is configured differently in this regard, and will need to have a different approach taken.

I did take a couple of pics, but they really don't tell much, other than it'* out of the way of everything.
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Old 04-17-2016, 03:27 PM   #2
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So you bypassed the heater core altogether?
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Old 04-17-2016, 04:03 PM   #3
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Quote:
Originally Posted by WilliamE View Post
So you bypassed the heater core altogether?
Yessir, at least for the time being. I was a bit chapped when my third unit failed, and with spring being here, summer is just around the corner, so I won't be missing it for quite some time.
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Old 04-17-2016, 07:48 PM   #4
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Ahh yeah, makes sense to say F it for a while then.
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Old 04-18-2016, 04:31 PM   #5
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At least he doesn't have to remove the entire dash assembly and RHS fender to change a heater core out.
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Old 04-18-2016, 05:01 PM   #6
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Holy moly, what vehicle requires all that to come off?
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Old 05-07-2016, 11:16 AM   #7
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I wanted to throw in a quick afterthought on this. Air is catching the disconnected heater hoses, and causing a whistling/whooshing through the dash, especially with a cross wind.

Either cap or pull the heater hoses, and your sanity will thank you.

That is all.
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Old 05-07-2016, 08:07 PM   #8
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Would it not have been easer to use these in 5/8 and 3/4?
Dorman Cooling Bypass Caps 02254 - Free Shipping on Orders Over $99 at Summit Racing
Every part store has them

Last edited by REGAL GUY; 05-07-2016 at 08:08 PM. Reason: added information
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Old 05-07-2016, 11:58 PM   #9
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Both heater hose pipes on the L27 are 3/4. Some have reported issues in some engines when the heater lines are blocked off. I didn't want to take a chance on possible overheat or cap blowout issues on a car that only has an idiot light (no gauge) to tell me that the engine has overheated, so I went down the safe road.
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Old 05-08-2016, 12:00 AM   #10
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Rjolly, think Mike is talking about Blazers/*-10'*....
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