Sniper Coolant Temperature Probe Location?

[farm truck]

OK - this may end up being a long post, so I appreciate your patience. I am also admittedly medium-skilled when it comes to the Chevy 350. I have had a million cars and bikes; this is my first GM product.

The issue is that the proper locations for the Sniper temperature probe (on the right or left side of the thermostat housing in the intake manifold) are unavailable. Standing in front of the truck, the RH threaded hole is plugged and this galvanized plug is HOPELESSLY stuck forever (picture 1)

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That's why I disconnected the temp probe for the dash temp gauge and put the Sniper probe in it's place. (picture 2)

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You can see the loose dash gauge temp lead in picture 1. Funny thing, the dash gauge still reads temperature! Here is where my knowledge hits a brick wall: is the sensor in picture number 3 for water? Or oil pressure? If it's for water temp, why would there have been two of them?

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So here is my two fold dilemma:

1. The Sniper gets up to temp just fine...... but I "think" that's because the previous owner DID put a lower temp thermostat in her (165F?). This truck rarely gets up to 195 F, and never in winter. I want to get the temp up, but not at the expense of low water flow across the Sniper probe.

2. Where to move the Sniper probe to when I put in the 195 F thermostat? Can I just drill a small hole in the thermostat, as I have read here and elsewhere? Or can I just add a tee on the heater core supply or return (pictures 4 & 5)? If so, which one is better?

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Thank you!

Chris

 

[gmbellew]

the dash gauge reads temp in-between cylinders 1 and 3 on that single wire sensor in pic 3. not sure what you disconnected up by the thermostat housing....maybe somebody had a second. aftermarket gauge for some reason?

 

[farm truck]

There could have been an aftermarket gauge installed sometime in the last 53 years for sure.

 

[ChuckN]

I would put it in the intake manifold itself, or in the cylinder head. Where it’s at right now, it will not pick up on the heat of the coolant accurately until the thermostat opens.

Edit- there is a pipe fitting threaded into the manifold in the first picture, it is to the right of the thermostat housing. That is a coolant passage.

 

[farm truck]

I would put it in the intake manifold itself, or in the cylinder head. Where it’s at right now, it will not pick up on the heat of the coolant accurately until the thermostat opens.

Edit- there is a pipe fitting threaded into the manifold in the first picture, it is to the right of the thermostat housing. That is a coolant passage.

I could just throw a tee in there, eh?

 

[ChuckN]

I could just throw a tee in there, eh?

Oh, I apologize- I misread about the plug that is permanently seized in the manifold, that’s where I would put it.

As far as the wiring goes, that’s an interesting issue. I had all kinds of wacky stuff going on with mine, and the wire colors had faded. Turns out the previous owner had switched the temp sensor wire with the electric choke wire.

That could be what is dangling there not connected. I’d have to recheck the wiring diagram though.

You could T-in for now, just won’t read anything right until the thermostat opens and releases the warm coolant.

 

[bluex]

Do not T the sniper sensor in. It needs to be in the coolant flow for a proper reading. If it's in a T then theres a possibility it gets an air bubble an a inaccurate reading. It's location is important for cold start an warm up performance. Personally I'd move it to the head an put the factory gauge one on the intake. If you mount the holley display where you can see it you can monitor temps from that.

Warm up will be faster an cold performance better with the sensor in the head as well.

OP didn't mention the year of the truck so if it was a factory tbi truck the sensor in the intake was for the tbi ecm.

 

[farm truck]

How about putting in the 195 thermostat and drilling a hole in it? Would that give it enough flow to read correctly, leaving the sensor in water neck?

 

[farm truck]

Do not T the sniper sensor in. It needs to be in the coolant flow for a proper reading. If it's in a T then theres a possibility it gets an air bubble an a inaccurate reading. It's location is important for cold start an warm up performance. Personally I'd move it to the head an put the factory gauge one on the intake. If you mount the holley display where you can see it you can monitor temps from that.

Warm up will be faster an cold performance better with the sensor in the head as well.

OP didn't mention the year of the truck so if it was a factory tbi truck the sensor in the intake was for the tbi ecm.

The handheld sensor is velcro'd to the carpet on the hump below the heater duct, visible with a slight dip of the eyes. Truck is a '70 GMC C2500.

 

[farm truck]

The handheld sensor is velcro'd to the carpet on the hump below the heater duct, visible with a slight dip of the eyes. Truck is a '70 GMC C2500.

Oh a couple more questions as I think that your suggestion is the way that I will go:

1. Is there another port anywhere on the heads, like the temp sensor hole between cylinders 1 and 3?

2. When I pull the sensor between 1 and 3 to put the Sniper probe in...... what size hole can I expect to find? Will it be a 1/2" NPT female threaded hole? I am expecting to see coolant gushing out, so I would have the 1/2" male X 3/8" brass bushing w/ Sniper probe tefloned and ready to insert to stop said flood, which I why I am asking about the hole size.

3. What about my idea of putting a 195F thermostat with a hole drilled in it into the water neck and leaving all of the sensors where they are now? Would this give enough coolant flow to the Sniper probe? Or am I an idjit for even contemplating this jerry-rigged fix?

 

[75gmck25]

Stock location for the dash gauge temp sensor is in the drivers side head where you found it, and it should be a green wire. It all looks correct. Some older iron heads had a 3/8” tapped hole, but newer 350 engines are usually 1/2”. My aftermarket aluminum heads have a 3/8” hole.

There is an identical tapped hole in the passenger side head and it works fine for a temp sensor. Its farther away from the thermostat, so it might be a little different temp than the other head, but that is usually not critical.

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I am using a 195 degree high flow thermostat (Robert Shaw, IIRC) and it works very well to keep the engine at about 190-195. It already has a drilled bypass hole, and it’s designed to provide a larger opening to help flow. I am also using a high flow cast iron water pump.

 

[farm truck]

Stock location for the dash gauge temp sensor is in the drivers side head where you found it, and it should be a green wire. It all looks correct. Some older iron heads had a 3/8” tapped hole, but newer 350 engines are usually 1/2”. My aftermarket aluminum heads have a 3/8” hole.

There is an identical tapped hole in the passenger side head and it works fine for a temp sensor. Its farther away from the thermostat, so it might be a little different temp than the other head, but that is usually not critical.

FlowKooler 330-195 FlowKooler Robertshaw Series High Performance Thermostats | Summit Racing

Free Shipping - FlowKooler Robertshaw Series High Performance Thermostats with qualifying orders of $109. Shop Thermostats, Mechanical at Summit Racing.

www.summitracing.com

I am using a 195 degree high flow thermostat (Robert Shaw, IIRC) and it works very well to keep the engine at about 190-195. It already has a drilled bypass hole, and it’s designed to provide a larger opening to help flow. I am also using a high flow cast iron water pump.

Thank you! Thermostat ordered!

 

[bluex]

My sniper sensor is the pass side head, an it works great there. It's been a while but I believe I had to use a 1/2 to 3/8 bushing for my stock 70s head.

There are alot of snipers running around with sensors in the intake. It's not terrible but I think from my experiences with multiple different platforms an installs that it functions better in the head. Sometimes that's not possible so I get it. If you have to leave it there because you can't get the plug out of the head then the thermostat @75gmck25 mentioned will help. If you ever pull the intake, have the plug below the thermostat removed an then put it there.

 

[ChuckN]

My sniper sensor is the pass side head, an it works great there. It's been a while but I believe I had to use a 1/2 to 3/8 bushing for my stock 70s head.

There are alot of snipers running around with sensors in the intake. It's not terrible but I think from my experiences with multiple different platforms an installs that it functions better in the head. Sometimes that's not possible so I get it. If you have to leave it there because you can't get the plug out of the head then the thermostat @75gmck25 mentioned will help. If you ever pull the intake, have the plug below the thermostat removed an then put it there.

I haven’t looked close yet @bluex - for those of us with old camelhump heads, is there still a water temp sensor fitting hole there? I looked around my headers with a light but the headers could be hiding it. If not, where did they put the temp sensors in the 60s cars? That’s why I have mine at the moment in the intake coolant passage.

 

[farm truck]

My sniper sensor is the pass side head, an it works great there. It's been a while but I believe I had to use a 1/2 to 3/8 bushing for my stock 70s head.

There are alot of snipers running around with sensors in the intake. It's not terrible but I think from my experiences with multiple different platforms an installs that it functions better in the head. Sometimes that's not possible so I get it. If you have to leave it there because you can't get the plug out of the head then the thermostat @75gmck25 mentioned will help. If you ever pull the intake, have the plug below the thermostat removed an then put it there.

Is the pass side fitting located towards the cab side of the head? I think mine is hiding, if so.