Running Hot - Why?

[mike_cyul]

My 1960 88" with 2.25 petrol is running just fine, and has done over 500 miles in the past few months. However, the water temp gauge (Jaeger, overhauled by Nisonger) shows the coolant (premix antifreeze) at 110/115C at full operating temp, and I don't quite understand why.

The engine and rad have been flushed (and I'm pretty sure there's no air in there). Timing is good, as is mixture. Brakes aren't binding. When re-assembling the thermostat housing, the thermostat (old Series 2 skirted type) was tested and the bellows appeared to operate correctly at the correct temperatures.

Temp gun shows the radiator to be doing its job, 95C at top, 55C middle, 20C at bottom, after a long run, with no cold spots. Core plug temps appear to show the temp gauge is relatively accurate. Nothing smells too hot, however, and there's no run-on after shut down, if that means anything.

Any ideas as to what could be making it still run hot?

Thanks,

Mike

[mearstrae]

Sounds like the thermostat isn't opening completely. Top hose temp should tell the story.

'95 R.R.C. Lwb
'76 Series III Hybrid 109
'70 Rover 3500S

[mike_cyul]

The top hose temp was 96C - would that confirm the thermostat not opening completely?

Thanks,

Mike

[mearstrae]

That would be my guess, the hose should be nearer your peak engine temp. There's also the chance that the pump is tired, or drive belt is loose, and just not moving the coolant. But I'd check the thermostat first.

"95 R.R.C. Lwb
'76 Series III Hybrid 109
'70 Rover 3500S

[jonnyc]

If all the temp readings are where they should be, but the gauge reads high, there must be a problem with the gauge. At least that's what makes sense to me. My first step would be to clean and tighten every electrical connection between the sensor and the gauge. After that, I would look for a water flow or thermostat issue.

[mike_cyul]

The temp readings taken off the engine seem to correlate with the gauge, so I don't think the problem is there. And in this case, it's not an electric gauge.

Water pump was recently overhauled, and the drive belt is within workshop manual specs, and so the thermostat could well be the culprit - although it did work when tested outside the engine before installation. It would be good to test with a different thermostat.

Anyone know a source of the skirted thermostats p/n 513465? Seem to be pretty scarce!

[artpeck]

Can I ask one question for clarity. Have you taken IR reads off of various places on the block and head etc? And if so what does that show. I ask as I chased a temp issue for awhile before confirming that the engine was running at proper temp and it was a gauge problem. I know yours isn't electric but it could still be working incorrectly. Otherwise I would take out the thermostat and test it in boiling water with a thermometer. You can also get a bubble so if you havent try elevating the front end and seeing if it burps.

[mike_cyul]

Yes, IR readings from several places. Gauge was indicating water temp of approx. 110C (hard to tell exactly, as the needle goes past the last setting, 100C, on the gauge). Temperature on the radiator top was 95C, middle was 55C, and bottom 18C (outside temp was 12C), no cold spots, so at least the radiator is working. Top hose was 95C. Themometer housing was 110C on top, as were the forward core plugs (couldn't reach the rear). Cylinder block around the sensor read 95C.

I did a run over some rough ground to shake things up a bit, and propped the nose up and that did let a bit of air out - but the temps were the same. There's a Kodiak Mk.II heater installed, and the hoses to and from were hot, so coolant was getting circulated there.

The thermometer was tested before installation and worked perfectly, but it may be time for another look. It would still be nice to have another one, to compare.