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Old 07-16-2013, 07:33 PM
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coolant flow direction in a 350 TBI

On my 93 Buick Roadmaster 350 tbi engine (same as 93 Caprice), 2 hoses go to the heater core, one directly from the radiator, one from the back of the intake manifold: which hose brings the hot water to the heater core?
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Old 07-17-2013, 05:57 AM
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heater

if the one hose that goes to the rad is on the top section ?? then the hose that comes from the engine is the supply and rad is return. it really don't matter for the heater is a small rad and don't care in or out.. it'll still work..
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Old 07-17-2013, 07:28 AM
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The heater hose on the back of the intake manifold is a 5/8" and is the heater core inlet. The return hose is a 3/4" hose. The hot coolant flows through the TBI manifold to the rear of the manifold and through the 5/8" heater core inlet hose. The fitting on the rear of the intake manifold is a "quick-disconnect" fitting. You should use a special 5/8" heater core inlet hose that has a metal tube end to be inserted into the QD fitting. Those special hoses are available from GM or from Dorman at a more resaonable price.

The heater core inlet hose fitting in the TBI manifold has a nylon restrictor in it to prevent over-pressurizing the heater core. Use a Dorman 800-401 or GM-15739936 fitting. Caution: This fitting should not be replaced unless absolutely necessary or you risk taking out the threads in the TBI manifold with it.

A special special tool is required to remove the QD heater core inlet hose and fitting from the TBI manifold. Dorman 800-408 and OTC 6046

Nylon heater hose fitting retainer and restrictor insert can be replace if necessary. Dorman 800-405 or GM-12543621

ASE Certified Mechanics hate those GM restrictor fittings and replace them with a standard nipple fitting, and a plain 5/8" heater hose with a standard hose clamp. Don't do it!

If you remove the heater hose restrictor fitting in the TBI manifold, it will shorten the life of your heater core .

Last edited by MouseFink; 07-17-2013 at 07:52 AM.
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Old 07-17-2013, 06:24 PM
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Quote:
Originally Posted by delawarebill View Post
if the one hose that goes to the rad is on the top section ?? then the hose that comes from the engine is the supply and rad is return. it really don't matter for the heater is a small rad and don't care in or out.. it'll still work..
For me, it does matter here because the aftermarket A/C I will be using has a valve that goes on the inlet hose to the heater core.
Mousefink, thanks for all these details! It seems the car I took the engine from has been modified already, no special fitting on the intake manifold, just a regular clamp!
Thanks guys!
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Old 07-18-2013, 06:07 AM
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Many vehicles do not have a troublesome quick-disconnect restrictor fitting because the owner has removed them. Most cars come with some sort of heater core restrictor. Some cars, like 1992-1996 Corvettes and Camaros, have a restrictor in the heater core inlet hose instead of a restricted fitting in the intake manifold. That type restrictor is a 5/8" O.D. x 1/4" I.D. nylon fitting that is located inside the heater core inlet hose. The heater core restrictor protects the heater core if the engine is run at high speeds and the water pump produces high pressure which can damage a heater core. A plastic Everco "Heater Control Valve" part #74796 is available at Autozone if you want to eliminate the stock restrictor fitting in the intake manifold and divert more coolant through the radiator or you can use a AC Delco 15-5511 heater control valve.

In addition to reducing pressure in the heater core, a heater core restrictor forces more coolant through the radiator for better engine cooling. Sometimes the lack of a restrictor in the heater core inlet hose may be a cause of engine overheating.

Last edited by MouseFink; 07-18-2013 at 06:20 AM.
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