Suddenly running hot

E-Type
1

Good afternoon. Let me provide something to think on while we are all confined.

Last fall, my '62 3.8 OTS started to run unusually warm on an afternoon drive. Like all, I am always keeping an eye on the temperature gauge. Where it typically ran 70-72 under almost all circumstances, it was starting to go to 90-95 after sitting in a little traffic, and very reluctant to cool down once under way. Only after 10-15 minutes of open 60 mph running would it get back to 90 and stay there until parked.

Once again, this came on suddenly. The only remotely possible action I took before this occurred was replacing of the somewhat crusty header tank with a new Stainless Steel copy from Welsh. I can’t say that the problem started immediately after as I don’t remember. In any event, I doubt the tank is at issue.

Actions taken last fall and the last two weeks;
Tested and replaced Otter switch, tested and replaced temperature sender, replaced gauge (unnecessary), installed Coolcat adjustable voltage stabilizer for gauge and calibrated with IR thermometer on black tape next to sending unit, tested 15 year correct Robertshaw sleeve thermostat (OK), redid upper and lower radiator hoses (soft), replaced water pump belt, flushed cooling system with Thermocure, then sufamic acid, then neutralized with sodium carbonate (I can see the fins and tubes in my 15 year old Howe aluminum radiator and they’re spotless), I’ve fattened up the mixture to no effect, run without thermostat without effect, coolant moving through head quickly when revving indicating water pump functional. Mallory dual point 8 BTDC at idle and 32 degrees all in at 2800 rpm confirmed. No visible leaks, 10 lb cap on overflow tank. Temps checked at all points with IR, radiator discharge 15 degrees less than intake.

Motor back round; rebuilt 15,000 miles ago (by me w/exception of head work done by the late John Miller at Straight Six Jaguar). 8:1 pistons with more aggressive cams. Engine has and continues to run fabulously with broad torque up to the red line.

Most importantly, I’ve been working on this problem for the last two weeks while the temperatures have been in the low 50’s here in Virginia. I fear the impact of summer temperatures on this problem.

Thank you in advance for any assistance rendered.

Cheers.

2

Hi and welcome. Did you just put in a new “Otter” (I think they’re repro) or did you go with the more reliable Coolcat switch? It comes on I think at 93, and stays on until it’s down in the 70s

What fan are you running with? Please don’t say the original eggbeater. I wouldn’t run that in Greenland. I tried it for about 3 months before ditching it.

Is the original shroud in place and sealed around the edges so it can generate max flow through the radiator?

You say it suddenly started and you were also doing things with the wiring. Is it possible you accidentally reversed the polarity to the fan motor? I changed my 64 to neg ground and forgot to swap the wires to the Coolcat fan and it ran much hotter than normal until I reversed them.

3

Thanks Erica. Installed Coolcat Otter. Running 10 blade Coolcat fan (pulling correctly)

4

I would provide a supplemental ground for your fan motor so you can test the fan motor itself. Sometimes the commutator or brushes get dirty to make fan operation intermittent. Sounds like your fan isn’t working.

5

Sooooooo… basically you are now reading a different sensor, with a different gauge. You have no clue how accurate they are, or are not. HIGHLY unlikely the engine would suddenly behave differently. MUCH more likely the gauge or sender has gone wonky.

Not sure I’ve EVER bought a new temp sensor that was even CLOSE to the right response. The gauges are at least a bit better, but unless you test BOTH, TOGETHER, you have no clue what the overall response is.

This is why my car now has modern, solid-state Temp and OP senders, and stepper-motor gauge movements. I got fed up with crap, unreliable, unpredictable senders (even the VDOs I’ve used) and dodgy gauges.

Regards,
Ray L.

1 Like
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Thanks Kris, fan coming on and off at prescribed temps correctly.

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Hi Ray. I ended up sending back the replacement gauge. The old sender was marginal and the new one kept. Once again… the gauge readings have been confirmed repeatedly with and IR therm many, many times at a wide range of gauges. Calibration between the sender and the gauge is possible with the Coolcat adjustable voltage regulator. Trust me, the gauge is accurate. It always was. I simply went through the motion of testing.

8

Sounds like you’ve checked, verified or replaced everything but the water pump.

9

Thanks John. Water moving fast through header tank when revving engine. Water pump has 15K miles on it.

10

Make sure your vacuum advance is working. Pull a vacuum on the diaphragm and it should hold. If you get a hole in the diaphragm you lose your vacuum advance and the engine will run hot.

11

Thanks Bill. Vacuum applied to advance, held nicely.

12

I was thinking vacuum capsule as well…have you revved engine to verify you are getting 40 or so degrees advance under no load?

13

Bill and Lee, just tried disconnecting vacuum line at idle. No difference in timing…hmmmm…

14

Water pump could still be the culprit. How is flow at idle? I’ve seen an impeller lose its grip on the shaft. Might be slipping, like having a loose belt. Speaking of which, how is your belt?

15

Vacuum advance won’t work at idle. It requires a partial throttle.Do a Google search on vacuum advance and look at the carburetor pictures. You will note that the hole for the vacuum advance is just behind the throttle plate.

16

Right…I would rev the engine with vacuum connected to simulate highway cruise, then check timing advance.

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Gentlemen, pulled vacuum capsule off Mallory and applied vacuum. Shaft moved and capsule held vacuum, so diaphragm has integrity. Checked vacuum line, nothing at idle or revs. This is where it gets bizarre; removing ignition take off plate at HD8, no vacuum coming out of small orifice, but out of screw hole for cover screw. Covering hole does not redirect to orifice. Clearly something is awry internally. Will investigate.

Thanks Jack. Belt is new and fine; turning appropriately. Will keep impeller loosening in mind going forward.

1 Like
18

…speaking of which…

I have seen an impeller worn down so much that it couldn’t pump water. You can guess how long it took me to figure that one out…

LLoyd

In our time, political speech and writing are largely the defense of the indefensible.

George Orwell

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Thermostats are a wear item. I think earlier in the thread you said you tested it. How did you do that? A new thermostat is cheap insurance.

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Vacuum line checks out, vacuum capsule ok. Will reassemble and re-check total advance tomorrow.

Bill, I boiled the thermostat (multiple, sleeve and standard) in water while measring temperature watching opening. Retested multiple times to confirm opening and closing temperatures. Generally starting opening at 160, fully open at 175. Also ran car without thermostat with same heating results.