Cooling System Problem Review - Chapter 6
 

Previous - see https://landroverforums.com/forum/ge...ter-5-a-51031/

Chapter 6 - Sensors and Heater Cores

D1 and D2 (and some others) have a small heated water line that goes in/out of the throttle body, and returns to the cooling system. The purpose is to prevent ice up of the throttle plate, which could stick open under certain conditions, even at temps in the 35 - 38 degree range. A leaking one can be bypassed, should not be confused with a head gasket leak. A repair kit is under $30.

The heater core in D2 and later D1 trucks (and others) gets hot coolant flow all the time engine is running, and damper vents inside HVAC unit under the dash move hot air where it is needed. Early D1's had a mechanical valve under the hood that cut flow to the heater core.

Heater cores can be reverse flushed, and checked for flow. Heater cores that leak and need to be replaced will introduce owner to the asembly line myth that the truck is built around the heater core. It is not a 15 minute job. Heater cores can be bypassed, they should not be stubbed off, but instead a loop of hose used to complete the path. In a D2 some of the heater core coolant flow impacts the thermostat operation.

Both trucks use a coolant temp sensor to tell the ECU what the engine temp is. If this sensor fails, ECU will think it is too cold, and apply more fuel. This sensor data can also be monitored with a scanner or an Ultra Guage from the OBDII port. The Ultra Gauge allows you display the temp, and set an alarm point for it.

The factory does supply temp gauges, on a D1 the gauge is driven by a separate sensor. The D2 uses a signal from the ECU to keep the gauge at the 50% spot until overheating begins. The D1 design accomplishes the same thing, above center point is overheating. It is important to note that you do not have to go to the end of the scale to be overheated. Note pix from two different trucks, two different temps, same reading on the dash gauge.

An important point is that with low coolant, the temp sensor may not be in the liquid. If sensor is just in the steam, readings may be more toward normal, while engine overheats. This would happen with a scanner as well.

next - https://landroverforums.com/forum/ge...ter-7-a-51044/

Did anyone else notice the RPM on that Ultraguage? hahahaha accurate.