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[robson]

My engine temperature appears to be very erratic it will go up to 75 stay there for a while then go up to 85-90 then back down to 75. Putting the heating on seems to drag it down .Do you think that this is a thermostat problem.

[Bumbazor]

Not necessarily; it could be an airlock in the cooling system.
If the thermostat is working properly and you have to put the heating on to drop the engine temp then something's not right.
I don't know the sysmptoms a failing thermostat gives though. Maybe someone can explain if this is symptomatic of such failure...
Have you recently done a coolant change or flushed the system?

[robson]

Havnt had the car long so no flushing as far as I know. Just seems funny that it goes up to normal 85-90 but then drops back to 75 your idea of an air lock sounds reasonable. Is it a matter of taking filler cap off and squeezing the hoses

[Bumbazor]

I don't actually know if taking the cap off will help, but if you do, do it with the engine off so you don't get hot coolant splahed onto you. I usually burp my hoses while it's running and at the same time I can feel the temperatures of them.
It's not normally difficult to remove airlocks and it doesn't cost anything, so try this first before going on to suspect faulty parts. It might also be a good idea to flush the heater matrix at the same time, but you will lose a bit of coolant if you do.

[robson]

Sorry I didnt read your post well .I dont put the heating on to drop the temp it just drops if I put it on. I dont have an overheating problem I wonder if the cooling fan is coming on early I will run the engine and check the temp that the cooling  fan comes on

[Bumbazor]

Whether you put the heating on to drop the engine temp or not, it shouldn't make such a big difference in the engine temperature. The fact that it does points to a possible problem somewhere.
If the thermometer is knackered the car won't know how hot the engine is and neither will you. If the car thinks it is in range it won't put the fans on, but when you put the heating on inside the cab, you provide additional cooling to the engine by way of coolant transfer and fan(s), and so the temperature of the engine drops.
You could have an overheating problem but I admit the normal 85-90 you mention is about right. However it's worth noting that is only an indicated temperature, not what it actually is (a bit like the speedo).
It could be as simple as a dodgy electrical connection to the thermometer. I can't remember if this can be reached while the engine is assembled, but it's a spade connector that pushes onto the coolant transfer bridge at the back of the V on the engine.

[tunnie]

does not suggest stat problems, usually it will get to 75 and stay there. As others said, when you turn the heating on, it shunts coolant into the heater matrix to give you eat, then carrys on its way, should not really make a difference to running temp.

Check for airlocks, might be worth flushing the heater matrix, also if check the temp sensor on the coolant bridge is not loose 

[mudflap]

mine does that when sitting in traffic, it gets hot though the electric fan kicks in and brings the temp down, that is with heater controls on full heat.

.

[Bumbazor]

You shouldn't have to have any cabin heating on in order for the engine temp to come down; it should put the fans on itself, and ciruclate coolant efficiently too.
Like we have mentioned, have a go at flushing the system, or at least the heater matrix.

[robson]

Tunnie do you know if the temp sensor connection is reachable and if so where

[Bumbazor]

...it's a spade connector that pushes onto the coolant transfer bridge at the back of the V on the engine.

At most you would have to remove the plenum and inlet manifold; not much really.

[robson]

The latest on this is that I started the car from cold and checked hose temps  The heater hose and the one going back into the water container soon warmed up but top hose cold when the indicator showed about 72 heat began to come into the top hose. Is this the correct temp at which the thermostat begins to open

[PhilRich]

AFAIK, 92degrees is the opening temp for the stat. Although the temp gauge on the dash is showing 72, it doesn't necessarily mean the actual water temperature is 72! you would need a live readout of the temperature to confirm the gauge was giving a correct reading.

[robson]

how do I get a live readout

[PhilRich]

With a code reader that gives live readouts I've got a cheapo "My Naff Code Reader" clone from e-gay which does most things