location for secondary coolant temp Sensor?

[lilymonster]

Looking to add a secondary coolant temp gauge (Isspro) to get a more accurate reading than the crappy factory gauge. I would obviously like to mount it towards the back of the engine on the passenger side if possible as this is believed to be the hottest area of the motor. Does anyone know if there is any "freeze plug" "port" "punch out" or anything of that sort to mount the sensor anywhere? If not, any recommended easy/convenient/logical place to tap in my own threaded hole to mount the sensor? Thanks for the help.

[sctrailrider]

I would think you could drill & tap the crossover plate on the rear of the head and that would be a good place and easy to get to.

[Robyn]

The Cyl heads have tapped ports that go into the water jacket on both ends.
The factory port up front on the left hand side is mirrored on the other head but only at the rear.

Or you can do as mentioned and use one of the crossover block off plates at the rear of the engine.

The old 6.2 engines used a crossover plate on the RH head (rear) to mount a temp sensor in.

Scare up one of those and a fresh gasket and you have a ready made access port.

Good luck

[lilymonster]

Thanks for the replies yall. I actually have an '86 6.2J layin around my shop from an old CUCV project and i did see the mirrored port to to the front one there on the back. I also noted however that this 6.2 (and another one I checked today in my friends CUCV) had clean c.o. plate back there without a sensor/port in it. It was interesting to note however that both motors had sensors in both the front and back water jacket ports. Just curious, why two sensors on this motor? I assume maybe one is for the glow system sensor and the other for the gauges? Seems dumb to not just have one sensor is this correct though? Do some 6.5 turbo engines have a sensor mounted back there already too? If so whats it for?

[Robyn]

The front port on the LH head is normally where the temp gauge is installed on the 6.2 and 6.5

The rear port on the 6.2 was fitted with a switch to control the COLD ADVANCE mechanism. This switch was closed until the water temp reached about 120F then opened to allow the cold advance and fast idle to shut off.

Some 6.2 engines in the mid 80's had another switch mounted in the block off plate, and this one was used to control the Glow inhibit function.

It was a bad idea then and now. The plan was, when the engine was warm the switch was open and this kept the glow system from working.

Sadly, what happened most often was the switch would fail in the open position leaving the glow plug system inoperative.

Many a 6.2 with this switch saw various metal objects, such as paper clips stuffed into the plug during cold weather to get the thing working.
Most of these got wrapped hastily with electrical tape and then sumarily forgoten, as things worked just fine without that anoying switch.

The later 6.2 engines 89-91 in the old style trucks and through 93 on the GMT400 trucks had one sensor in the water Xover up front that fed the ECM the needed information and then the various functions such as the glow plugs and cold advance/idle were all handled that way.

The 92-93 6.5 engines with the DB2 mechanical pumps had a very similar system.

With the 94 model year and the electronic injection system, the entire control is handled by the one cts (coolant temp sensor) in the Xover up front.

The one sesnor in the LH front (in the head) is just for the temp gauge

You are quite correct that the rear of the block is the hottest, being the two back cylinders.

BUTTTTTTTTTTTTTT the coolant rises there into the cylinder head and heads north to where it exits the head and on to the radiator.

The front port where the temp gauge reads is probably the best spot to read whats happening.

Sadly there are areas in the head that allow the coolant to stagnate and actual "steam pockets" can form.

This is why GM went to the dual stat Xover and the HO water pump.
The flow through the block was increased a BUNCH to keep the steam pockets from forming and to also get a better flow through the radiator too.

Mostly it was to stop coolant stagnation in the block.

The rear two cylinders are always fit up slightly looser (about .0005") than the front 6

Anyway, hope this helps

Missy

[lilymonster]

So would you say that the front left is the best place for the sensor even if you have the updated HO water pump and 97+ dual thermostat upgrades ? Or are you still likely to ready overall more accurately in the front sensor?

[DmaxMaverick]

Be careful to not over-engineer it. It didn't work for Edsel.

The actual temperature isn't what's important, as long as it's within an acceptable range. It's just a number and doesn't really mean anything. What is important is the trend. If you can track a trend, you can identify trouble on the way. Unless your original gage or sender is broken, I think you'll be surprised to find how inaccurate it isn't. And, having 2 devices showing you the same analog may not be a good idea, either.

Something my grandfather told me when I was very young: "A man with one watch always knows the time. A man with two is never sure"

[lilymonster]

Yes, our elders do give us much good advise, however there is one old expression I just can't subscribe to and that an old guy I know to me and that is "Ignorance is Bliss". So I decided to go with the option of installing my ISSPRO gauge sensor in the pictured cross block off plate which I sourced from an old "core" 6.2 diesel engine I've got laying around. Thanks for that tip.

Ive found I don't pay much if ANY attention to the crummy stock gauge cluster anyway... There is nothing there I care about..... Besides maybe fuel level and that is a once-a-week type of deal. I have a Canadian truck and I live in the USA so my speedo is in kilometers so that doesn't really tell me anything and oil pressure I suppose I glace at but that's about it. Instead I find my self constantly looking the panel you see in the second photo....