Hey folks, I’m hoping someone can point me in the right direction with an issue I’m having. I’ve got an RRC with a swapped 300 TDI engine (originally a VM 2.5). The engine’s recently rebuilt and runs great—no smoke aside from a little black puff on startup and under hard acceleration, which seems normal enough.A while back, I swapped out the temperature sender (green band), and since then, the temp gauge has been sitting comfortably below the halfway mark. But over the last few days, I’ve noticed it creeping up higher, especially after driving for about 20 minutes. It’s not hitting the red, but it’s getting up to about 3/4 on the gauge. I’ve got an electric fan that kicks on fine, and I can see coolant moving in the clear tank. I also checked the thermostat with an IR thermometer, and it’s not going above 90°C at the thermostat housing .I’m stumped—could this be an airlock, a head gasket issue, or just a dodgy sensor? It’s only started happening recently, so I’m wondering what’s changed. Any ideas or troubleshooting tips would be massively appreciated! Thanks in advance.
Help Needed - Temperature Gauge Creeping Up on Rebuilt 300 TDI Engine
- Thread starter portokali
- Start date
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- North Shropshire
Had the coolant level changed at all recently? Is the radiator getting hot? What about the cabin heater?
I think the coolant level is the same but will keep an eye on it. The radiator seemed like its getting hot, and so were both hoses. The cabin heater is bypassed for now.
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- 36,185
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- North Shropshire
72c? What's that reading from? Does the engine *feel* too hot? That's not too hot for core engine temp, maybe the sensor has gone bad?
It's measured from top of thermostat housing. Yes i agree, seems ok. Not sure why the temperature creeps up on the gauge though as the sensor was replaced recently.
I would jury rig some temporary temperature gauge set up for testing purposes, until you are sure the engine is good and you are not going to wreck it.
A cheap mulitmeter that accepts K series sensors will do, or cappiliary sensors are the best
A cheap mulitmeter that accepts K series sensors will do, or cappiliary sensors are the best
That's a good idea. If overheating what could be the main culprits? My radiator is still the brass one. Which i did rinse and back flush but maybe it's time for a new one. I noticed my green coolant turned slightly reddish.
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Give the engine and radiator a good flush, the cabin heater too if you can. No reason to replace the radiator unless it's damaged beyond repair, most blockages can be fixed
Always stat first, tdi can run rad so fecked they are only fit for scrap and not over heat.
Are the small coolant air bleed pipes still present?
Is the coolant system pressurising by to much when at operating temperature?
Anaconda
Well-Known Member
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We fitted a new rad to a 200tdi a few years back, made a big difference.
Thanks for all the input. I measured the resistance of the sensor and used IR at to measure C at thermo housing. Seems it tops out at 3/4 of gauge and 50 ohms, around 70 degrees. Outcome is that the resistance of sensor is quite low, and gauge seems to be expecting 160 ohms to read in the middle. Is there a different thermistor I could use(currently using green)?
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Installed a new sensor and after 20 minutes the gauge does the same thing - goes to 3/4. Strangely enough, the gauge dips slightly when i press on the brakes and if I turn off the engine and restart it goes back down to below 1/2. I am now thinking it's an electrical issue...either a short or ground issue. I checked grounds and they all seem to be in good shape. Probably need to take apart the dash next but has anyone had similar issues?
