Help please - temperature gauge problem

Help for the technically disadvantaged please. Driving last night for about 30 minutes when the temperature gauge suddenly shot up into the red. Was almost home so continued on with the needle in the red. Despite a couple of minutes with the needle right down to zero, it has remained at red. I waited til the engine cooled and checked the coolant, which was fine. Started the engine and let it run for five minutes and watched the gauge sweep up into the red. The fan at the back of the radiator did not start up at all. What do I need to check next? This is my first car and I'm not very knowledgable so any help appreciated, ta.

fan switch....waterpump belt....if thermostat is opening....

thanks for the quick reply. first things first, how do i check the fan switch?

the fan is switched via the ecu martos, from the coolant temp switch (under the distributor)
is the heater hot ?

frank

Hello again. When you ask is the heater hot do you mean the radiator? In the Haynes manual it suggests disconnecting the fan and connecting it to a 12v to see that it works. Does this mean run a lead from the battery? Help!

Hi Martos, does the gauge return to a normal reading if you tap the instrument panel ?.

Both my micras had the same problem but the gauge would return to normal after lightly hitting the instrument panel. Turned out to be electrical connection problem at the back of the instrument panel and it was not actually overheating.

Hi there. I gave the instrument panel a few taps but it didn't move the dial, sadly. What I have noticed is that, with the engine cold, when I start the engine the gauge (which is still up in the red) comes down quickly to about half-way, and then creeps up to the red again over a few minutes. The gauge used to start at zero, then creep up to about halfway after driving for a while. The fact that I am in Scotland and there's ice on the bonnet when I started the car might suggest that the engine is not as hot as the dial would suggest?

Ran the engine for ten minutes today. Dial shot up into the red as before. Fan still didn't kick in. Had a check in the engine straight after. Radiator - cold to the touch. Radiator cap - cold to the touch. Hose number 1 at the back of the radiator - cold. Hose number 2 under the distributor, slightly warm. If the engine was overheating there should be some sign of heat, yes?

The reason he asked if the heater was hot is because the heat from the heatercore inside the dash is a byproduct of water heated up by the engine flowing through the small radiator (often referred to as a heatercore) inside the dash. When the engine heats up, the water is heated up and that same water used to cool the engine is used to heat up the heatercore - if the heater is warm it means that the heatercore is getting hot water flowing through it and if it's really hot as your temp gauge might suggest, you should get very warm-to-hot air coming out of the interior vents when the heat is turned right up and the fan's on.

---dens

you could have a faulty gauge, mine was and it would do the same flicking up to hot and staying for a while, then returning intermitently. Can you try another instrument cluster/gauge from another micra?

I fixed mine by finding and repairing a faulty conection on the back of the circuit board, on the back of the cluster

Swapped the instrument panel from my mate's micra and the temp gauge shot into the red so it's not a faulty gauge.
With regard to the heater, the temp gauge is in the red but the air is coming through cool. Takes about 5 minutes (as it usually does) before the warm air comes through.

Just lost my massive reply to your post 'cause I accidentally logged myself out. Anyhow, bottom line is - it sounds like it's either a thermostat issue or a sensor issue. For some reason I keep remembering there's two water temp sensors for the engine (one for ECU, one for gauge cluster) but can't be 100% sure without my workshop manual/haynes with me.

The delay before the heater working sounds normal so there's a good chance that the engine is heating up as normal but the fact that the gauge is already at max makes me think it's a sender issue. I don't know if there's one or two but at least one of them is in the head of the engine on the gearbox side. It's worth swapping it with a mate's one or from a wreckers (breakers) to see if that fixes the issue.

Good luck :)

Edit: Here's an excerpt from Haynes giving resistance values at given temps. I suppose it's worth testing resistances with your current sender if you can.



---dens

dens is right, there are 2 senders, the gauge one is the skinny one with a single wire (under the dizzy)

frank

Actually given the values that are shown in the above image, you could simply short out the single wire going to the temp sensor to test it - that said, if you ground the wire going from the gauge cluster, the gauge should go as hot as possible as there's 0 resistance. I don't know how well you'll be able to troubleshoot with this info but I suppose somehow it might help determine the cause of the issue.

---dens

Thanks for the replies. If my mate agrees will try swapping the sensors. Is coolant going to spill out when I try to remove these?

it will trickle out martos, and they,re pretty inaccessible, i would test the resistance first or get another sensor and wedge it against the head, and check the gauge

frank

Hi there. When you said inaccessable, you weren't kidding. Here's what the Haynes manual says about the coolant sensor in the picture. If I can disconnect the wire to the sender and switch the ignition on - if the dial drops to the cold end of the scale the sender unit is proved faulty. Sounds nice and easy with no coolant spilling worries, but I cannot find the sender!

it aint that bad ! :d

Thanks for the replies and the pic. It helped! Finally got what I hope was the coolant sender unplugged. It did have a thicker wire though, but hopefully I got it right. Tried ignition and sure enough, needle straight down to zero, which according to Haynes means the sender is faulty. Being of a suspicious nature, however, I'm going to try the same thing on my mate's Micra tomorrow to see if his does (hopefully not) the same thing. Anytime something goes wrong with the car I don't expect to get away with a cheap repair! If anyone wants to chip in with the science of why the sender is faulty for reading zero when unplugged, go for it!
Anyway loads of thanks for the help so far!

I may not be the best when it comes to electronics but from just having a basic understanding of how the sender works, the reason it shows zero temp on the gauge when disconnected is because there's essentially infinite resistance to ground. If the wire were grounded then it would have zero resistance to ground, thereby giving the exact opposite reading on the gauge (hot hot hot!).

If the sender is faulty, it could be internally broken/shorted to the point where it's just always grounded completely to the engine or body of the sender and it shows it as such on the gauge. In effect it would show the same reading as it is if you shorted the wire to the body/engine. When the temp of the water heats up, the resistance of the sender is meant to change at certain points (as shown by the table above). Unfortunately I can't really offer much more than just 'it might be shorting/grounding'. The real test will come when you get your hands on a known good sender and chuck it in there.

---dens

Just saw my old post here and thought I should mention that the fault was def with the coolant temp sensor and the gauge was back to normal with the new part fitted.

hi mate just wondered how you fixed the problem? same thing happening to mine took it apart and when i fidle with the wires seems fine but goes back to the top when i connect it back up?
help will be greatly appreciated thanks!