Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Tyre Pressures 2014 Roadster

FWIW I've never seen the temperature gauge move from it's slightly under half scale position once engine of my 3.7 Roadster is warmed up. This remained the case after fitting larger aluminium radiator the only difference being the two speed fan comes on to low speed far more rarely. I did record a peak OBD2 temp whilst on a dyno test of 112°C but didn't have the opportunity to see the gauge then. As Jon suggests the cooling system appears very resilient to all engine demands. Illustrated write up below of same below based on my observations:





The Roadster 3.7 V6 cooling system can be explained with the help of this Mustang engine cutaway image and that of lower inlet manifold. This appears to be moulded from a hard, hopefully non heat conducting, composite and is bolted in the V of the engine to seal with heads. It incorporates on the underside a hot coolant rail (tube) running horizontally down it's middle, mating to water jackets on rear of each cylinder head. Hot coolant flows forwards along the rail protruding to seal via "O" ring to a casting bolted to front face of engine (identified by blue label on cutaway) passing coolant via union to large bore top hose and radiator. The inlet manifold also has a hose union at rear fed from coolant rail to accommodate rubber hose feed to cabin heater matrix inlet (bottom union). In this way the hottest coolant in the engine reaches both the radiator and heater in most expeditious manner without the need for long rubber hoses. The casting provides the narrower bore permanent radiator bypass (part with cast-in text) running down to a mixing chamber below (shown as cutaway) to provide quickest warm up. The bottom hose of rad feeds to the thermostat housing bolted to bottom of casting mixing chamber with the temperature sensing side of enclosed thermostat facing inwards so directly onto bypass flow. This chamber also takes coolant from the return of permanently fed cabin heater circuit (see hose union) via a T piece which accomodates a head of coolant from the lowest point of header tank above.

When engine coolant warms sufficiently the stat begins to open allowing a cooled flow from radiator to be mixed in with the bypass and heater return. The turbulence from various flows into the mixing chamber mitigating the temp of very hot coolant from bypass circuit, the greatest influence being from the radiator cooled flow as the larger bore rad plumbing gives a preferred path for coolant, providing stat is open or partially so. The chamber outlet interfaces directly to pump casting inlet with actual water pump below, then pushing coolant upwards from lower part of engine block waterways. In this way the stat is able to control coolant temperature through a wide range of engine power demands (confirmed by near constant temp gauge) whilst always providing maximum temperature coolant to heater matrix.

The header tank accomodates two very narrow bore bleed/vent hoses from top of rad and top coolant rail with connection to latter seen adjacent to blue label. These assist bleeding and equalise levels throughout the system as coolant expands. The tank has markings for max and min levels with plenty of room above coolant level to allow for expansion as coolant heats when pressure within will rise, hence need for its pressure release filler cap, should system be overfilled. The upper mark should be checked to match top of radiator level since the clear plastic tank is a re-purposed moulding from a Ford Focus installation. Experience suggests coolant level is not critical although overfilling should be avoided.

The radiator, whether OE plastic side tank or conventional design taller after market all aluminium replacement, is further cooled when necessary by a two speed cooling fan. The only difference is it will run far less often with the latter, and when it does is far quieter due to fan assembly being attached directly to radiator without the OE cowling interface. The two fan speeds are ECU triggered by excessive coolant temperature via one of two relays dedicated to each fan speed, with a high wattage Ford resistor being brought into circuit to limit motor current for lower.