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[tr6canuck]

Recently my tr6 started overheating, well not boiling over, just reaching 3/4 mark.  Before taking it to my british mechanic last week it ran below 1/2 in the morning, 1/2 in the afternoon on a hot day driving down the road and 5/8 in traffic.  I took the car in last week to install an e/fan and have the carbs rebuilt.  The mechanic also set the timing.  Now it runs hot all the time.  Over the w/end, I flushed and changed the coolant, changed thermostat and fan belt.  Yet the engine is still running hot, close to 3/4 even at night.  I turned the heater on and off, but no change in temp.  I narrowed it down to 3 things: bad water pump, faulty gauge or faulty temp sensor in thermostat housing.  Or possibly a combination of those 3.

Any thoughts??

Update: I took the fan belt off and spun the water pump by hand.  It seems to turn freely without any noise.  What about the water heater valve?  Could that be bad?  How would I test it to see if that's the culprit?

[TR3driver]

Not likely to be the heater valve, unless it is visibly leaking.

I would be double-checking the accuracy of the temp gauge.  It relies on a gizmo known as a "voltage stabilizer"; and if the VS fails the gauge will read approx 1/4 scale higher than it should.

One quick way to test VS operation is to pull the wire off the temp sender, turn the key on and measure the voltage from the wire to ground.  If the VS is working (and is the original style), after a few seconds, you should see the voltage start switching between full battery voltage and zero.

[tr6canuck]

I swapped out the temp guage with a used one from my mechanic.  Same reading.  I  phoned my brother in law and he said pop the rad cap and see if the coolant is flowing.  Sure enough it wasn't.  I replaced the water pump and checked the rad.  It was flowing good.  I test drove it last night and it was running fine. 

This morning, it was getting warm at the lights.  (I took the mech fan off).  I pulled over and noticed the new electric fan wasn't on.  I checked the fuse (my mechanic wired it to the existing fuse that controls the signal lights and a few gauges which kept blowing the 35 amp fuse, I put it on its own circuit with a 25 amp fuse as recommended by Hayden) and it had blown.  I ended up replacing the fuse twice, but it was still getting hot at the lights.  Now I think the fan motor is kaput.  So now I'm going to revert to the mech fan to be safe.  It's a shame as I could really feel the difference in power.

TR6Canuck   

[TR3driver]

Just a thought; when you put the fan on it's own 25 amp fuse, what type of fuse did you use?  The stock Lucas fuses are rated using a different, obsolete system; which produces roughly twice the rating of modern fuses.  IOW, if you used a Lucas 25 amp fuse, it wasn't big enough for the fan.

Also worth checking to see that the fan is not mechanically binding somehow.  Sometimes the plastic blade and/or housing can distort and cause problems.

[tr6canuck]

I use standard glass tube fuses from an Auto store.  I wired it using the spare fuse location of the fusebox.  I'm using a rheostat, which is a pain to adjust.  I should have went with a preset.  My mechanic put the temp probe inside the hose between the thermostat and rad vs between the rad fins as Hayden instructs.  Not sure if that is causing any issues.  To be safe I'm putting the old fan back on.  The fan is on the front side so it isn't subject to all the engine heat.  I checked and it does move freely.

*Also, when I pulled over to check if the e/fan was on and blowing air through the rad it didn't seem to drop the temp. 

[TR3driver]

I'm using a rheostat,

Hopefully, that means you have an adjustable fan controller, rather than just a rheostat in series with the fan!

My mechanic put the temp probe inside the hose between the thermostat and rad vs between the rad fins as Hayden instructs.  Not sure if that is causing any issues.

Should be fine. 

*Also, when I pulled over to check if the e/fan was on and blowing air through the rad it didn't seem to drop the temp. 

There is enough inertia involved that it can take some time to see the results of the fan running.  Plus, the temperature tends to rise at first when you pull over, since the coolant is moving slower but there is still a lot of heat in the engine block/head.

For a "stress test" (and to adjust the controller), I would suggest just letting it idle in your driveway.  That way you can see when the fan comes on and off, and what the temp gauge is doing at the time.  If you want, you could even monitor the temperature at various points with a "infrared" thermometer (although be warned that it likely won't be accurate when shooting the aluminum thermostat housing). http://www.harborfreight.com/non-contact-pocket-thermometer-93983.html

But, blowing the fuse pretty clearly indicates there is a problem, so you need to deal with that.  One possibility might be that the fuse clips in the original fuse holder aren't making a good connection to the fuse.  BTDT, except w/headlights.

[tr6canuck]

Well, I put the mech fan back on.  i left the e/fan on.  it has an adjustment knob that you turn with a screwdriver.  i turned the rheostat adjustment so it won't kick in to see if the mech fan makes a difference.  y/day i was playing with the adjustment and sometimes it would kick in and sometimes it wouldn't.  i don't care for it and plan on getting a preset so i know it will kick in at 185f.  y/day i thought the fan motor went kaput as it didn't kick in after i put a 2nd fuse in even with the gauge at 3/4.  perhaps i need to check the wiring and see if it has a good connection.  i bought a $30 infrared thermal gun from autozone.  the aluminum thermostat housing was reading much cooler than the hose, so i couldn't get a proper reading.  with the mech fan back on the temp guage is running at 1/4 on the highway and 3/8 in stop and go traffic.  not sure yet about being stationary for an extended period of time.  so i think i'm good with my cooling.  now i can work on putting in new seatbelts.

thanks for all your input.

UPDATE:  Going home I was stuck in traffic at the border and temp guage spiked to 3/4.  The e/fan blew a fuse.  I replaced it, but it didn't turn on.  The engine started running wierd.  Luckily I was able to get it back on the road and cool it down.  No idea why it got so hot.  I have an aluminum rad shroud.  Perhaps the rad needs changing?  Maybe when I flushed it out it loosened up some crud that created a blockage.  Not sure what else it could be.  It never got this hot before I started fixing the cooling system.

[BobH]

Maybe really check your timing, too--as you were running fine 'til you had it set.  To far advanced will overheat.  Newer (heh) tr6's had a vacuum retard on the distributor (as I recall) that  would retard the timing when the coolant got hot.

-BobH