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A heat management system of a gas turbine engine for cooling oil and heating fuel, includes an oil circuit having parallel connected first and second branches. The first branch includes a fuel/oil heat exchanger and a first fixed restrictor in series and the second branch includes an air cooled oil

A heat management system of a gas turbine engine for cooling oil and heating fuel, includes an oil circuit having parallel connected first and second branches. The first branch includes a fuel/oil heat exchanger and a first fixed restrictor in series and the second branch includes an air cooled oil cooler and a second fixed restrictor. The first and second fixed restrictors limit respective oil flows through the first and second branch differently, in response to viscosity changes of the oil caused by temperature changes of the oil during engine operation to modify oil distribution between the first and second branches.

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1. A method of managing oil cooling and fuel heating in a gas turbine engine, the method comprising: a) distributing oil from a pumped oil supply into first and second oil flows, the second oil flow being parallel to the first oil flow;b) transferring heat from the first oil flow to a fuel flow;c) u

1. A method of managing oil cooling and fuel heating in a gas turbine engine, the method comprising: a) distributing oil from a pumped oil supply into first and second oil flows, the second oil flow being parallel to the first oil flow;b) transferring heat from the first oil flow to a fuel flow;c) using ambient air to cool the second oil flow; andd) using a first fixed restrictor and a second fixed restrictor to respectively limit the first and second oil flows differently, in response to viscosity changes of the oil caused by temperature changes of the oil during engine operation, comprising directing the first oil flow through the first fixed restrictor including a diaphragm having a flow orifice, and directing the second oil flow through the second fixed restrictor including a plurality of holes extending though a body, the plurality of holes being smaller in diameter and longer in axial length than the flow orifice of the first fixed restrictor. 2. The method as defined in claim 1 comprising calibrating the first fixed restrictor to allow a maximum flow rate, thereby preventing the fuel flow from being overheated. 3. The method as defined in claim 1 comprising directing the first oil flow to bypass the first fixed restrictor when an oil pressure build-up of the first and second oil flows reaches a predetermined level. 4. The method as defined in claim 1 comprising combining the first and second oil flows after step (d) and directing the combined first and second oil flows into an engine oil manifold. 5. The method as defined in claim 1, wherein the flow orifice of the first fixed restrictor has an annular edge having an edge tip angle of less than 90 degrees. 6. The method as defined in claim 1, wherein the flow orifice of the first fixed restrictor is an angled flow orifice.