Coolant temperature sensor 993 EFI

Just bought a 1996 Hijetta Devon camper. Love it already! Read up lots about overheating Hijets, so imagine my surprise when driving it home to discover the temp gauge never goes above cold. It just seems to go up to just over the bottom line, then dive down randomly, then creep up a bit......and just generally hover about.
The drive home was from Leeds to Cheshire on the motorway at decent speeds, plus I've done some little local journeys and just kept it idling on the drive. The gauge always does exactly the same thing.
Engine performance, coolant level, heater output etc. all seem fine, so I'm wondering about the sensor. Question is, where the hell is it & is it easy to check/change? A photo of it in position would speak a thousand words if anyone would be kind enough to do that.
Thanks in anticipation.

Did I speak to you earlier on the phone?

What do the pipes feel like? Does the return hose under the radiator get hot?

Does the gauge ever move when its stood still running?

Temp sensors are known to be a possible fault on a 993cc

The sensor is in the rear of the cylinder head, crawl under the passenger sliding door with a torch.

I think there are two - one with 2 wires, one with 1 wire. Gauge sensor is the one with 1 wire I think.

Thanks for the response. No - it wasn't me you spoke to!
I haven't checked pipes etc. yet. Tried it idling when stood still this evening, even keeping the revs up. It just creeps up gradually a little bit, the drops down, creeps up a bit again.....it does exactly this when driving it at all sorts of speeds too. The drop back down seems sudden and random.

It might have no thermostat in it.

Funny I spoke to a lad earlier with a Hijet Pickup with a camper box on the back, who was getting the head done.

I don't understand why having no thermostat would mean it never reaches operating temperature. Surely the thermostat is fully open when the engine is hot and you are bowling along, so no thermostat would just mean it takes longer to get warm.
I've tried revving, standing still and on the motorway going up hills, but the needle can actually go down.

With no thermostat an engine never get past the luke warm stage.

The thermostat acts as a variable restricted throttling water flow to maintain its target temperature.

With no thermostat, the radiator will actually displace more heat than is being generated.

HighlyJetted is right, I had a Peugeot 106 and that had no thermostat in when I bought it. It would never warm up and would stay below 1/4 on the gauge and moved quite sporadically. Once I replaced it it started overheating and quite soon after the head gasket blew. The previous owner obviously removed it to mask the overheating problem. As overheating is common on these vans I would guess that's what has happened here too.

Just a word of advice when you are removing the thermostat housing, they become VERY brittle on these so be very very careful with it, I can't stress that enough!

Ah, okay. I'll have a proper look when I can, but just to ask: if there is plenty of heat from the heater, but the temp gauge shows cold, does it mean the gauge is the fault?

Definitely still a possibility! In my 106 the heater was cold when i first bought it and the overheating problem was caused by a blocked heater matrix.

I'm sure HighlyJetted has written a thread on here on how to test your temperature sensors along with other sensors.

https://hijet.forumotion.com/t1794-test-your-suspected-faulty-sensors



Heater matrix is piped off the coolant bypass feed on the side of the block so more than likely will have more heat than the rest of the system.

But as you suggest, I would test the sensor first.

But the 1 litre sensor is different than the 1.3, but the test is still similar in basis, as the gauge is interchangeable I think.

Nice one, ive just had a read and it is based on the 1300, would the figures be the same for the 993 Matt?

But the 1 litre sensor is different than the 1.3, but the test is still similar in basis, as the gauge is interchangeable I think.

Ok, one more then I'll give you a rest! Just done a road test - ragged it a bit, then sat on drive idling:
Temp gauge got to nearly half (a first!) as I sped along, then just suddenly dropped like a stone to just above bottom line as I continued along at the same speed.
Loads of heat from heater, bottom hose on radiator warm.
On drive way, gauge went up to quarter, at which point the fan cut in. It did this three times, always at quarter point.
This all seems erratic to me.
Is it possible to have a gauge which under-reads - ie. when it says quarter, it is really at normal operating temperature?

Connect a multi meter to the temp sensor and get it warm, write a little resistance table - e.g. write down the resistance every 30 seconds.

Not sure to be honest, I guess its possible. Strange that the fan is coming on at 1/4. To me for some reason the 2 temp sensors aren't reading the same so you could have either a faulty sensor or the one sensor (the gauge one) isn't submerged in coolant properly I.e an airlock or low coolant. Have you checked the level of coolant by removing the radiator style cap under the passenger seat?

Fan is controlled by the fan switch in the bottom pipe.

So there could be coolant in the bottom pipe and none in the head?

The 993 fan sensor is in the bottom of the rad and the thermostat housing is on the rear of the inlet manifold and metal looks a bit like a Ford cross flow/valencia type. the clocks in the dash are inerchangeable with the 1300 only difference is an extra fuel light in the 1300. The needles on the gauges pull off and there is no mechanical stop so take the plastic front off the clocks run up till the fan kicks in and pull the needle off using a wire clothes peg and refit pointing about 5/8 up the scale then it will be in about the correct place.

Sudden temp guage drop usually means the thermostat has opened and let cold (cooler) water into the engine.

rich the mechanic wrote:..... The needles on the gauges pull off and there is no mechanical stop ............ .

I have always been puzzled as to why you keep saying that there is no stop on the gauges. My vehicle is 1996 (same as yours I think) and is equipped with stop pins on all gauges. In fact the reason the speedometer rests at 6mph is because the needle is up against the stop and can go no further.

The only thing I can think of is that they are black, the same as the background, and so not easily noticeable but they are there (unless someone in the past has been 'cutomising').

bushwhacker wrote:

rich the mechanic wrote:..... The needles on the gauges pull off and there is no mechanical stop ............ .

I have always been puzzled as to why you keep saying that there is no stop on the gauges. My vehicle is 1996 (same as yours I think) and is equipped with stop pins on all gauges. In fact the reason the speedometer rests at 6mph is because the needle is up against the stop and can go no further.

The only thing I can think of is that they are black, the same as the background, and so not easily noticeable but they are there (unless someone in the past has been 'cutomising').

Mine is a '95 only the needles have a stop but the mechanisms don't have stop point as they are sensor driven. I have had both a 1.3 and 1lt clocks apart while tring to sort out making a white insert and if you take the needles of these two with no power on them and refit in the same place more than a few seconds they will be in a different point to how they were with the temp needle you can position it to be halfway up the scale when doing a cold start and run off the top of the scale when warm, I have my fuel gauge set that it never shows more than 3/4 full but loads under the empty point as the 1lt has no warning light.

I had a look for my water coolant temp sensor as i think they or one need replacing, going to test them hopefully using HJ thread on testing them in ohms, i have taken some pictures, is it them? noticed mattom wanted some pictures too. this is on a 2003 1.3 petrol/lpg panel van hijet (in profile pic)

Not being a mechanical expert but does that top pic not show the exhaust so wouldnt that be the lambda sensor not a temp sensor?

Possibly, I know atleast one of them isn't a sensor as there are only two. I was hoping someone could point me in the right direction

As an educated guess I would say picture two is the temp sensor, two wires and looks to be screwed into the block. The third pic looks to show only a single cable going to the connection plus a big thick cable which I presume would possibly be starter motor...as I said educated guess...but I could be completely wrong and prove myself to be uneducated

yeah, picture two was my best guess too, hmm, im sure i will soon find out, think i'll tackle the rust first though, more important while im away for 6 months over winter