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Discussion Starter · #1 ·
Does the 1987 EC 305 have a water bypass? I had a new 350/290 crate motor installed in my EC and an Edelbrock 3701 Performer intake manifold. This intake does not have provisions for a bypass. Iit is overheating at idle. Is goes from 190 deg. up to 210 in 5 minutes or so, and continues to climb.
The timing is set correctly, fan clutch seems to be working (I think), I put a 180 degree thermostat in it. It has a new radiator, water pump, and belts. The higher temperatures are even raising the transmission temperature.

I got two answers from GM about the water bypass. The first said it was needed, the second person I talked to said that since the new motor was not a Vortex motor, that it was not required and the first guy was wrong. He said the 350/290 has internal bypass down behind the water pump.

When I got the EC back from the install, I was given the old manifold and some heater hose with a "T" in it. I belive that one side of the "T" went to a nipple at the rear of the manifold. Could this be the water bypass and is it needed on the new crate 350/290 (non Vortex) motor?


Jim
 

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Jim, as far as I know there is not some other bypass hose or steam vent hose needed for a gen1 crate engine. I 'm leaning twoards thinking you have one or more traditional issues.
Timing set retarded due to wrong timing marker or method?
Defective thermostat, heat it up in water on stove with thermometer to check if opening @180*.
New radiator not large enough capacity? I have the Modine heat buster 4 core copper radiator I think it was called now cooling down my LS1. This multi-application radiator has an inlet under cap which I think some vehicles had a tee from a radiator hose to it,maybe your water pump requires this?? My LS1 uses it for steam venting,yours may need it for trapped air pockets. Also check that lower hose isn't collapsing.
Fan obviously can cause overheating at idle, if you think it's ok shut engine off when hot, clutch should be stiff.
Hope this helps some, I don't know every detail on every model.:secret:
 

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Jim, I had the 3701 on my L69 engine, and I remember plumbing in the "Bypass" to the heater hose with a tee like you described. There is a port on the top rear of the intake manifold that I used. I remember it was a tight fit- I think I had to use a 90 degree fitting to make it work.

The primary purpose of this bypass was to eliminate any air trapped in the engine. I do not have this now with my TPI, so I always l park on an incline, radiator on the high side, when I have to re-fill the radiator. Leaving the cap off, I let the engine run, heater on full hot, as I fill the radiator. I use a funnel that seats in the opening, so I can get a slight overfill as it is warming up. You will see air bubbles coming up in the opening. You will also see a noticeable change in level when the thermostat opens up. Be careful- I have had it spit hot water at me at times. Keep going until you see almost no bubbles. To be sure, I would follow this procedure a couple of times, letting it cool down between fills. ( All the tee was doing was letting any trapped air run out through the heater hose).

HTH
 

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No bypass should be necessary, your problem lies elsewhere.

Is your radiator sealed to the core support?
Do you have the correct fan shroud?
Is your radiator cap new or at least sealing properly?
Does your lower hose have the spiral wire in it?

I am not aware that GM ever plumbed the rear of the intake on a carbureted motor, even though there is a connection port back there, but then I've never owned a chevy as new as an 87 so I could be mistaken, my 83 Z-28 certainly didnt plumb that connection.
 

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Discussion Starter · #5 ·
Jim, as far as I know there is not some other bypass hose or steam vent hose needed for a gen1 crate engine. I 'm leaning twoards thinking you have one or more traditional issues.
Timing set retarded due to wrong timing marker or method?
Defective thermostat, heat it up in water on stove with thermometer to check if opening @180*.
New radiator not large enough capacity? I have the Modine heat buster 4 core copper radiator I think it was called now cooling down my LS1. This multi-application radiator has an inlet under cap which I think some vehicles had a tee from a radiator hose to it,maybe your water pump requires this?? My LS1 uses it for steam venting,yours may need it for trapped air pockets. Also check that lower hose isn't collapsing.
Fan obviously can cause overheating at idle, if you think it's ok shut engine off when hot, clutch should be stiff.
Hope this helps some, I don't know every detail on every model.:secret:
i'm in the process of getting the bubbles out of the system as Darbysan suggested. We reset the timing to exact specs. (10 deg. btdc 32 max.) . I'm going to check out that radiator. I'm also thinking about a supplemental electric fan I could switch on and off. I'm trying to get the EC set up so I can tow my vintage trailers occasionaly, so keeping it cool is important.

Jim
 

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I saw this from another thread about the fan clutch !
"With the engine hot and engine off, try to spin the the blades by hand, if it spins more than two or three blades replace it.
Or, if you have the engine running and hot, observe the fan as you shut the engine down. If the fan does not stop and continues to spin after you shut the engine down, replace it."
 
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