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Radiators for the automatic version of my car have a couple of extra coolant outlets at the bottom for cooling the auto transmission. I was sent the wrong radiator and I don't need these in my manual car. Would there be anything wrong with just connecting the two with a length of hose?

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  • Does it physically fit in the space for the radiator? Do the bolt holes line up? – computercarguy Mar 13 at 16:00
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Depends on the design.

If those ports are connected to the same fluid channels in the radiator then you will need to blank them or connect together.

Many have a separate radiator built into the same structure and the auto box cooling portion is designed to have oil flowing through it. This means you can just leave it or blank as you wish.

I used that autobox cooling portion to heat diesel fuel in one conversion I did... seemed to work fine.

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    I’m with Mike on this. Those two ports are for a transmission fluid cooler (which is inside the plastic end tank of that radiator). No attachment to anything necessary. Just leave those ports unconnected. Drive on. – zipzit Mar 13 at 7:33
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    Would having an empty inner tank have any cooling efficiency implications? I think there could be a performance increase if it were filled with some kind of heating oil and plugged. – Aww_Geez Mar 13 at 15:24
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    @SolarMike If the tank were empty, it is effectively empty space in the radiator as it won't conduct well, but if it were full of a heating oil it could act as more of a heat sink / conductive surface. Cooling performance is what I'm getting at. – Aww_Geez Mar 13 at 15:36
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    @SolarMike it occurs to me now that having a completely sealed container of anything that could heat up is a bad idea. – Aww_Geez Mar 13 at 15:54
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    @Aww_Geez but if it is left empty then it could collapse from the surrounding cooling system pressure... – Solar Mike Mar 13 at 16:45
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That’s not for coolant

That is for Automatic Transmission Fluid. Inside your radiator is another little tiny radiator that interchanges heat between the ATF and the coolant. This flows both ways: if the ATF is hotter than the coolant, e.g. Lots of heavy torque converter work, it keeps it at sane temperature. If the ATF is cooler than the coolant, it warms up the transmission (e.g. sit there for 10 minutes idling, or you are at freeway cruise in torque converter lockup for 2 hours where the automatic is doing nothing).

Your stick-shift doesn't need this; the milliseconds you spend spinning up synchros doesn't make enough heat to matter.

Its presence saves the manufacturer and parts dealers the inventory cost of stocking 2 radiators instead of 1. You can use it for anything or nothing.

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    Some manual vehicles have transmission and differential coolers - for a reason... – Solar Mike Mar 14 at 4:29
  • @SolarMike Did not know that. Good to know. – Harper - Reinstate Monica Mar 14 at 7:19
  • @Harper-ReinstateMonica Thanks - I thought it would move coolant to the tranny, not transmission fluid to the radiator. – MeltingDog Mar 18 at 6:17

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