heater hose question 
heater hose question
In general.. your discharge from pump to the heater core is usually smaller in dia. that would be your 5/8" hose and your return which is usually large in dia, 3/4".
If you look at your A/C and your Power Steering system, the high pressure line is usually smaller in size and the return line (usually low pressure) is usually larger in size.
If you look at your A/C and your Power Steering system, the high pressure line is usually smaller in size and the return line (usually low pressure) is usually larger in size.
GM usually set the heater lines up so that pressure is retained for the inlet and relieved for the outlet. This means the larger nipples are the return, the smaller nipples are the feed. Just connect the small one on the water pump to the small one on you rheater core.
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Staging Lane
Joined: Jul 2007
Posts: 85
Likes: 0
From: Chicago
unless your tubing sizes match, it really doesnt matter.
heater cores aren't directional, so even if you'd hook it up backwards, it would still flow fine.
so if you got 2 same size fittings on heater core, just use whatever works best/easiest.
heater cores aren't directional, so even if you'd hook it up backwards, it would still flow fine.
so if you got 2 same size fittings on heater core, just use whatever works best/easiest.
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Verdad Gallardo I beg to differ on that statement. While I cannot say for all of them, there are several cores that sit higher than the coolant level of the engine block and would fill up with air if the coolant flow was reversed.
davy check this link if u are talking about blocking out the ports at the water pump this should be the answer 
https://ls1tech.com/forums/showpost....2&postcount=17
https://ls1tech.com/forums/showpost....2&postcount=17
While we're on the subject how exactly does the heater core work? I mean the two lines coming off of the water pump transfer heated coolant through the heater core obviously but is that coolant run through before or after the thermostate. What i mean is that coolant based on radiator temperature or engine temperature. I ask because it seems like Duramax NEVER heats up and acts as though the entire radiator must heat up befor i get heat and yet my LT1 has heat in under 5 minutes.
It depends on the system, some have a valve that controls coolant flow into the core and some have full flow all of the time and use a system of flapper doors to direct air over the core or around the core depending on how much heat is desired.
The diesel also doesn't get anywhere near as warm as a gas motor. I keep mine plugged in all winter, and it still takes a while to warm up. Even with the front cover, it it is below 0, I will go out and start the truck, flip on the seat heaters, and go back inside until the truck runs a high idle cycle (this can take 25 minutes or so). Compression engines just don't generate the heat that spark engines do, this is a big part of the efficiencies and lifespan of a deisel.
Staging Lane
Joined: Jul 2007
Posts: 85
Likes: 0
From: Chicago
sure, but tell me why if you pull the thermostat, you could access both "feed" and "return" without much being in the way?
There is a GM part number ( and other vendors) for a U shaped hose to act as a bypass loop for the heater ports on the pump.. if you search, I am sure someone has already posted the part number.
