Two different points to install water temp sender? Which is

[QWKDTSN]

I installed my water temp sender in the drivers' side cylinder head as shown in the JTR manual (page 3-10, item 6). Then yesterday I got my Performer RPM Air-Gap manifold and discovered that there's a spot to mount it near the water neck. I checked out my school's Camaro (Our auto shop built it to compete at the city's legal drags) and the sender is mounted on the intake manifold. Also on page 1-9 in the JTR manual I can see that it's mounted there as well. Which spot should I use? Is one more accurate than another? I would think that the sender being right next to the water neck would have a drastically different temperature reading than in the cylinder heads. I guess one or the other should be plugged up. What would you guys reccommend? I know, I know, I need to get an SBC manual, right now just about everything I know's come out of the JTR manual

[Guest Anonymous]

The temp at the front of the motor may tend to be slightly lower than temps sensed at the rear of the head closer to the combustion chamber heat. I prefer to want to know the highest temp reading in the motor, knowing that the rest will be cooler.

[Owen]

Good point there, I have mine installed at the water neck also. But which is the "correct" way and which is the "best" way?

 

Owen

[Tim240z]

Most factory installs are at the thermostat. I have to believe that the manufacturers put some thought into this

All of the V8 racing engines I have seen, have the sender (mechanical) located at the thermostat...must be a good reason for this.

Tim

[pparaska]

I like the position under the thermostat because I get to see what the thremostat sees. Then again, it'd be cool to have several senders and a rotary switch to read them independently. My old 461 heads don't have holes for senders, so that's a moot point for me.

[Guest Anonymous]

For my peace of mind, correct temp sensing would be the method which allows the driver to determine when excessive head gasket damaging heat is being developed anywhere in the engine.

The highest furthest forward point on a motor might not necessarily be the hottest. It is a fact that rear cylinders, (and in our Chev V8's the two center cylinders on each side in particular) want to run hotter than the front cylinders. (Two exhaust ports side by side)

Heat sensed nearest any two center cylinders would will give a more accurate discussion of highest engine temp. Heat development in

a motor may appear homogenized at the thermostat because it is. Coolant from all cylinders must exit through this point.

It isn't the coolest cylinders that one needs to worry about. It is the hot ones that usually have problems. A head gasket leak from a combustion chamber anywhere in the cooling system is like being just a little bit pregnant.

Temp gauges would be unnecessary if the metallurgy and materials could survive unlimited heat numbers. The very purpose of a temp gauge is to forewarn of impending damage caused by excessive heat build up and a blended heat signal is not the best indicator of this.

My 1971 350 V8 K20 4X4 Chev pickup uses a sensor in both heads near the center cylinders and uses both grounding signals to display the hottest temp it sees. I would have to disagree with the "most temp senders are in the manifold" assessment; or that the factory boys intentions can be derived by such a statement. Unfortunately, to many factory decisions on this level come down to cost effectiveness not best accuracy. If you are running a high compression engine, cylinder head temps become even more critical. Detonation occurs just about anytime the cumulative cylinder fuel charge temp exceeds 400 degrees. Gasoline molecules cease to burn and sublimate at these temps. It isn't possible for the human ear to hear detonation. But for the fact that all detonation occurs with some degree of pinging, we wouldn't hear it all. The difference between pinging and detonation when decribed in FPS is a ten fold increase, with commensurate head gasket, piston damaging cylinder pressures being developed.

Most cooling systems can only drop the temp of the coolant by 20 to 25 degrees in one pass through the radiator. This fact means that the coolant returning to the motor can rapidly gain heat under extreme engine loads.

Overheating is like a stop sign, the further off you can see either coming, the sooner you can deal with both safetly.

I have a collection of detonated pistons, valves and rings which I keep to show clients why overheating cannot be ignored. The saddest cases are the ones where a simple failure to check total advance results in the destruction of brand new motors in mere minutes of startup and test drive. A good cooling system absorbs the extra heat without showing the huge cylinder temps and pressures until it is too late.

In conclusion I would vote for "best" and "correct" being any temp sensing system which allows the longest most trouble free use of the engine.

[Datsun660z]

Here is an OLD post I found searching for the answer to a question I have. (But of course didn't find) If you have the temp sending unit installed at the Thermostat housing, And it reads 200 degrees Fahrenheit what should it read when moved to the cylinder head?

 

Thank you,

[Datsun660z]

Anyone?

[strotter]

I've installed a late-model GM f.i. system from an '89 Firebird onto a 327. I have an aluminum manifold installed. There are *three* temperature sensors in this configuration: in the cylinder head driver's side for the computer, in the cylinder head passenger side for the fan relay, and in the intake manifold behind the thermostat for the gauge. From the beginning, I noticed that the computer consistently sees slightly lower though more consistent temps than the gauge. I initially thought it was one or more bad senders /gauges, bought new senders, calibrated them (pot of heating water and and a DVM), calibrated the gauge as well, and got the same results (I have a "thing" about accurate instrumentation). By all rights, I would think that the sender in the head would see the highest temps - but wait. That area is "earlier" in the cooling loop than the thermostat. Perhaps it sees cooler temps (and we're talking 10 - 15 degrees F here) because the coolant has more recently run through the radiator. Doesn't the coolant flow from the radiator to the pump, then through the block past the cylinders, and then into the heads from outboard to inboard, then to the manifold and thermostat? With the sender on the outboard of the heads, they are seeing temps *before* the coolant passes the combustion chambers, where they'll pick up a significant heat load before going to the thermostat. What I'm thinking now is that the gauge is seeing "transient" temperature spikes to a greater extent than the computer because of the widely varying temps in the combustion chamber itself, as opposed to the "general" or "overall" heat load of the block. Why would GM do this? I'm thinking that there might be a couple of reasons. For sure, the gauge is the lowest priority sensor, but offers a measure of control over the whole system - if the operator sees a high temp, he'll back off a bit, easing the load. This is good, from a designer's point of view, so you actually want the most "pessimistic" possible readout. The fan, however, shouldn't see those spikes, as it would cycle on and off unnecessarily leading to premature failure. The computer, too, should see more consistent temp readings, else if might get stuck in some kind of hysteresis. Also, it can be programmed so as to "know" about any potentially low reading, and compensate accordingly. Some of the calibrations in the eprom lead me to believe that's correct.

 

So if my logic is correct, I would say, get the most consistent reading from the cylinder heads, though they may not reflect temperature spikes you might want to know about; or, get the most pessimistic readings from the manifold, and compensate for spikes by understanding the dynamics of the engine from experience.

 

What was the original question?