Engine heating up then dropping back down?!

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Sat May 25, 2013 12:36 am

If the engine races during warm up but then drops down when fully warm, that definitely indicates the ECT (coolant sensor that feeds the ecu) is knackered, but doesn't explain the guage not showing hot, as that is a separate sensor.

So for both to be faulty would suggest either air lock in the cooling system, or a fault on the loom to the 2 temperature senders/that loom's not plugged in properly?

kris_aka_edu · Post by **kris_aka_edu** » Sat May 25, 2013 9:37 am

I know it's not economical I've owned two. Since its happened its using a lot more fuel than usual

kris_aka_edu · Post by **kris_aka_edu** » Sat May 25, 2013 9:38 am

Wurly, I've not got a clue mate! Aaaaaaaaah!

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Sat May 25, 2013 9:55 am

Well we'll see what we can sort for you.

BMCC · Post by **BMCC** » Sat May 25, 2013 9:57 am

If you've got a multi meter put it to resistance and check the ECT when the car is cold first thing. Then take it out for a spin and get it up to temp so that you can see it resistance when hot. The difference should be massive. There a re values on the net for what you should expect the resistance to be. The 5th gen should be about 5k ohms cold and about 250 ohms hot. If this checks out then I'd test the wires back to the ECU for continuity & voltage.

Riverghost · Post by **Riverghost** » Sat May 25, 2013 10:04 am

hope you find out the problem mate! got a similar problem with my heat shooting up and dropping down, im personally hoping its an airlock still

Post by **Vtecmec** » Sat May 25, 2013 10:12 am

As Wurly intimated, it is unlikely to be the sensors as both the ECT and gauge sender unit would have to be faulty.

A fluxing coolant temp reading usually indicates:

Air in the coolant system
Coolant leak that does the same as above
Head Gasket

kris_aka_edu · Post by **kris_aka_edu** » Sat May 25, 2013 10:13 am

http://bit.ly/10T1JUM ?? That's an eBay link from my phone hopefully it works

kris_aka_edu · Post by **kris_aka_edu** » Sat May 25, 2013 10:14 am

It's not ever getting up to half way, so I'm assuming that rules out head gasket?

BMCC · Post by **BMCC** » Sat May 25, 2013 10:23 am

Both the gauge sensor and the ECT sensor are thermal resistors. They can get slow over the years, it's not impossible that both are knackered together after all i think they are a few cms apart? So why not test them and rule them out (along with the wiring).

I had a similar problem with my Pulsar except that it the gauge would always say the car was over heating. New gauge sensor, new ECT and new stat, all was fine. With the pulsar all three were goosed although the stat was sticking open a bit because of a big bit of silicone.