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Tech Article

M20 Throttle Body - Thin Coolant Hoses

Last Updated: 05/08/2021
Parts Group: Throttle body without throttle position sensor
This article discusses the thin coolant hoses attached to the throttle body for the M20 engine with the main focus being on the routing. If you are not here for the technical analysis but would rather buy a used unit from us, guaranteed to work and fit, then please select a link below.
The information herein is based on my own car, and used parts that I have bought from various junkyards.

In cold temperatures, there is some danger of the throttle body icing up. To counteract this, some motors provide heat to the throttle body. One way of doing this is to run coolant through a section of the throttle body so that the coolant makes contact with the metal of the throttle body and transfers some of its heat while doing so.

One such example is the M20B27 engine as found on a 1984 325e that I analyzed today. The remainder of this article focuses on this engine, in this context. From what I recall seeing, I consider it likely that my observations apply to all M20 engines.

The throttle body is attached to the intake manifold such that the throttle position sensor is at the bottom of the throttle body. With this orientation, there is a top metal nipple and a bottom metal nipple. Each is intended for the attachment of a thin coolant hose; one for coolant inflow and the other for coolant outflow.

The thin coolant hose attached to the bottom metal nipple on the throttle body leads to the thin metal nipple on the thermostat housing. This nipple is on the engine side of the thermostat housing, presumably so that coolant can flow to provide some heat to the throttle body even before the thermostat has opened.

The thin coolant hose attached to the top metal nipple on the throttle body leads to an attachment point on the engine block, toward the rear and just below the where head meets the block; a couple of inches above the starter.
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