Temperature dropping off when heaters on

[iiPaul]

I've just changed the thermostat this afternoon due to having a faulty one. So I changed it, left it running with the expansion cap off and topped up the coolant as necessary and it gets up to temp fine. But when I turn the heaters on hot full blast the temperature gauge drops to about halfway. Any ideas? Thanks

[DanHarper]

Is it not fairly normal if you idle a diesel? The engine only generates so much heat, and if you're drawing it all in to the cabin the coolant temperature is going to fall...

[Tech1e]

The temp gauge should only go to halfway anyhow.

[iiPaul]

It's only dropped off since I've replaced the thermostat, that's all

[coskev]

The thermostat is fully open once the cars at normal temp,so it won't affect the heat.

Have you took it for a drive and tried it after?

Was the stat the same temp as the one removed?

[iiPaul]

Yeah I took it for a 15 minute drive and its still the same.

It's pretty much the same temp as the old one, maybe just a tiny bit lower

[coskev]

What mix of coolant have you used?

[iiPaul]

I used prestone 50/50 mix ready to use coolant

[coskev]

Does it deffo get cooler?

The air into car feels cooler?

[iiPaul]

The heaters still work fine, Get both hot and cold.

[coskev]

Maybe the sensor for gauge is dodgy after fresh coolant?

I would get a laser thermometer and check temps of the coolant system near the gauge sender when it's showing a drop in temp,will tell you if it's really getting cooler or its just a dodgy sender.

[kellaway86]

You didnt buy your thermostat from eurocarparts did you?