Bypass heater core, now running hotter?

I bypassed the heater core in my 66 289, and I am running a cut piece of heater hose from the outlet on the water pump to the intake manifold in lieu of the heater core. Since I have done this, the car has been running @ 210-225 at highway speeds, but at idle it will slowly drop back down.

The lower rad hose has the spring in it
It is a new OE style 3 row radiator
Water pump is newer
I flushed the block and the radiator until only clean clear tap water was running out
I have a 160* T-stat (Am changing to a 180, but I doubt this is the cause)

The upper hose gets hot when it opens, and everything appears to work just fine.

With the bypass hose, most of the coolant just recirculating back into the block because there is less resistance than going through the thermostat?
Should I put a restriction/blockoff plate in the hose?

This is during summer weather, around 85-90 ambient temps. The car doesn't overheat, it just runs hotter than I am used to (165-180)

10secgoal said:

The heater core acts like a mini radiator. So now you have lost it's (small)cooling benefits. You should have a 180 in there. You want the water temp hot enough to get the oil temp to at least 215 to burn off moisture in your oil.

If you running hotter at speed than idle, you have a problem. you water isn't circulating fast enough. Blocked radiator or something of the sorts.

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I flushed the radiator completely clean and its pretty much brand new (less than 100 miles on it)

Is it possible I have a defective radiator? The water flows through it very easily when I put a hose in the top. It is an autozone OEM replacement. I was going to go aluminum but the stock one worked ok, so I figured why not

I will check temps at the upper hose and lower hose, but the circulation is good when the cap is off. Maybe I just really suck at bleeding the coolant system and there is a huge air bubble.

2+2GT said:

This did nothing to improve cooling, in fact the reduced restriction of the hose vs. the heater may have made it worse. What you should do is have your heater connected normally, and splice a manual shutoff valve in the hose between the intake and the firewall. Factory AC cars had an automatic valve in this hose to improve cooling.

Use a 190° thermostat, it's what the engine was designed for, both for performance and economy.

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My goal wasnt to improve performance, it was half I wanted to use it as a radiator for my water cooled computer, and half weight reduction and removal of a possible weak link/leak point and to clean up the engine bay

I will get a 180 or 195* t-stat and put a restrictor in the heater hose

btw the heatercore did an excellent job as a radiator in my computer



and no heaterhoses makes my engine bay happy

That was it, I capped off the lines and now its running as cool as ever.