Overheating that's not really overheating...

[Stalkersam_9]

Hi folks,

I hope you might be able to point me in the right direction on this one.

Tidied up some wiring on my 1.9DG, cutting out bad bits, replacing and also replacing corroded connectors. Top job.

Except now i seem to have an overheating issue, that isn't really overheating...

To get the point, i go for a run and temp is fine. About 2/3 of the way up and stable. As soon as i get back and leave the engine idling, temp jumps right to the top in just a couple of minutes and the red light comes on.

Radiator is warm but not red hot and there's no water coming out of the back tanks, no bubbling, hissing or anything. Engine bay is hot but not overly.

What's more if i hold the revs a bit above idle (let's call it 2,000 rpm ish) the temp goes back down and the red light goes off.

So, the question is where do i start replacing bits/testing bits please?

One final thing to add - one of the wires and connectors i replaced was to what i now believe is the temp sender (bottom left of engine block). Could it simply be that is faulty?

Other thought is water pump (doesn't work properly at low revs?) or thermostat?

Thanks in advance for your thoughts and advice.

Simon

[DoubleOSeven]

Is the dual speed fan for the radiator coming on? There’s a sensor in the bottom of the rad.

[tandemsandy]

i spent over a year chasing a similar thing on our Mazda 323f. Temp gauge would suddenly go to max but never any signs she was actually overheating. Other electrical use (eg using the electric windows) suddenly brought the gauge back down.

To cut a long story short, it was a failed engine block earth cable inside a connector.

Rob

[Forden341]

Have you checked the water level or maybe a faulty level relay, #42 or #43?
I seem to remember reading somewhere that the early water cooled level relays were set to bring on the red light and send the gauge soaring when the level dropped.

[captain Byrne]

What's more if i hold the revs a bit above idle (let's call it 2,000 rpm ish) the temp goes back down and the red light goes off.

I'd say you need to top up your water. When you rev the engine the water pump pressurises the system raising the coolant level so the low level sensor senses the coolant and all is good. When the revs drop the system is de-pressurised & the coolant level drops to a level below the low level sensor which will then trigger the alarm.

[Stalkersam_9]

Thanks everyone for your replies.

I'll start and work through these and see what i can find.

DoubleOSeven - The fan does come on, but not when it's sat idling. However, the radiator is not that hot at that point. You can out your hand on it.

Tandemsadny - Thanks. As i've already found a lot of corroded wires and connectors that's a good shout. May just be some others i need to sort.

Forden341 - Water level is all good. One of the first things i checked. Relays however i've not looked at. What are they? And how do i check if they're knackered? Thanks.

captain Byrne - That does sound just like the issue but water level is good (unless it's losing water for some reason). Will check it again and make sure it's full but pretty sure it is as it was something i checked when it first happened.

Thanks again.

Simon

[CJH]

I'd say you need to top up your water. When you rev the engine the water pump pressurises the system raising the coolant level ...

In my experience the coolant level goes down when you rev the engine - that's how I squeeze more fluid into the tank when I'm refilling and bleeding. I think the pressure from the water pump causes the hoses to expand a little, so the volume increases.