Hey all,

I had an issue with my car today on the drives to and from work.

It seems that when I am moving, car runs at a normal temperature and everything seems fine.
Once I slow down or stop however, the temperature starts to rise. It hasn't rose much above 3/4 yet, I've managed to prevent that but it is still a huge issue.
I thought straight away that it would be the radiator fan (I even turn on the air-con in the hope it would help). To test this, when I got home I turned the car on and waited to see if the fan kicked in.
It did.
So apparently the fan is actually working when I just turn the car on and don't move. But once I start driving I am having issues.
Does anyone have any ideas about what could cause this? I have no issue replacing the fan, but it seems to be working so I'm not going to just throw money at that. Ideas, advice or answers are very welcome here as I need my car to be good to drive (I've just started a new job!).

Cheers,
Sam.

From my limited experience there could couple of issues, your thermostat does not open completely so when you drive the water pump pressure foreces it open and when idling it closes. The second problem could be your temperature sensor malfunction, I had the same issue which was resolved after replacing it.

This might sound a little strange, but it did happen to me, I had a fluctuating temp needle, and wierdly, it was the earth strap from the intake manifold to firewall (top & centre), give it a clean and retighten, after that, I'd check the relay, then the sensor itself or thermostat.

While it may well be the sensor, the relay is easier to check, without removing any radiator fluids, a quick trip to the wreckers should net you a relay or two.
I doubt the temps should rise so quickly in winter. So the earth or sensor or thermostat seem likely, but not excluding the relay.
IIRC, the fan should start immediately with the AC. I'll check now.
Yep Immediately.

Just to clarify - the temperature was rising quite fast, I could see the needle moving upwards with a glance down of 2 seconds or so. Which makes it sound like an issue with the thermostat and related components.
Phew. That's a bit of a load off my chest.
I will check the earth tomorrow when I get home and the relays as well.
In regards to checking the sensor, how would I go about doing that?

Have you checked the coolant level in the radiator and overflow?

Forgot to mention that.
I checked the coolant level and it was a bit low, which is odd because the car recently got an engine swap at Mits-fix and I replaced all the radiator hoses and the radiator. I filled it up, but forgot to check the overflow.
Any particular reason why you are asking?

My first suspicion would be your thermostat, it may be sticking closed. Your engine runs normal at speed, you have more air running through it, when you stop after speed is when your engine will run hottest and needs the thermostat open to cool more effectively.

I had the opposite, my thermostat was sticking open, the engine didnt get warm enough unless stopped and my fuel consumption sucked until it was replaced.

Since you've recently replaced the hoses and coolant, I'd redo the filling procedure, Start with a cold engine, open the radiator car and top up, replace the cap, top up the coolant in the overflow bottle, then start the engine. This is the inportant bit, constantly watch the coolant level and keep topping it up, if you dont do this you can end with a water defecit, or an airlock almost in the coolant passages in the engine, continue to monitor till the Temp gauge reads normal.

If you fill the radiator and the coolant bottle and leave it at that, the result is exactly what you ghave described. So that could be worth chaecking as well.

Yeah I will fill it up properly using that procedure and go from there. Thanks for all the help so far guys and I will keep you all posted :)

Since you've recently replaced the hoses and coolant, I'd redo the filling procedure, Start with a cold engine, open the radiator car and top up, replace the cap, top up the coolant in the overflow bottle, then start the engine. This is the inportant bit, constantly watch the coolant level and keep topping it up, if you dont do this you can end with a water defecit, or an airlock almost in the coolant passages in the engine, continue to monitor till the Temp gauge reads normal.

If you fill the radiator and the coolant bottle and leave it at that, the result is exactly what you ghave described. So that could be worth chaecking as well.

Hmm, I think over the years I have filled more than enought empty systems to know how to do this lol

The engine was purchased from another member, no issues that I am aware of.

Sam, you need to drop in so I can pressure test, either way, a small drop will not account for the temp rise, generally a thermostat will not either as movement will not speed up coolant flow that fast either

The temp drop is airflow, if it happens again, hit your AC and see if this also drops the temp

When you have some time, drop by and we will do a few tests

Forgot to mention that.
I checked the coolant level and it was a bit low, which is odd because the car recently got an engine swap at Mits-fix and I replaced all the radiator hoses and the radiator. I filled it up, but forgot to check the overflow.
Any particular reason why you are asking?

As shoot already answered, if theres air in the system the thermostat could have trouble reading the temp and surge, I wasn't sure how to word it other than "bubbles" though.

Thanks for all the help guys.

Mal - I'll give you a call about when I can make it down. Will most likely be Monday afternoon if that suits.

Cheers.