Michael Yount
Mustang Master
You simply can't rely on the stock gauge for that - you're gonna have to add a decent gauge that actually tells you the temperature.
When can we say the engine is over-heating with autometer gauge
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Black Sun 5.0
Founding Member
I'm having a similar problem, I'm getting an SN95 fan installed this week. I'm through with the stock setup.
Michael Yount
Mustang Master
The factory gauges/senders have hysteresis designed in to keep the gauge from moving around a lot at the normal operating range of temps. And they're all a little different. I still don't think anyone should conclude much of anything based on the factory gauge. Get a quality calibrated gauge that actually reads out temps - and then you'll know what you're dealing with for sure. Also, the ecu was designed for an engine with cast iron heads, not one with aluminum heads. They won't take quite the abuse that the stock cast iron heads will. So I don't think the factory ecu limit for killing the a/c is necessarily a reliable indicator of what's safe with an aluminum head engine.
Don, you are a brave man. my stock gauge wont pass the mid point (~200*), even when the aftermarket gauge is heading north. i would soil myself if i saw the stocker reading 3/4 high. Michael is right on: the stockers suck, and all seem to perform differently.
Michael, excellent point about alum vs iron heads - i missed the idea of relating the factory thresholds to what is safe or acceptable. when i grow up, i wanna be and think like you.
Michael, excellent point about alum vs iron heads - i missed the idea of relating the factory thresholds to what is safe or acceptable. when i grow up, i wanna be and think like you.
Yep, like I said though, it is fairly rare. I have however seen it once or twice and both cases were poorly maintained (or possibly lack there of) cooling systems. Upon inspection however after tearing down the water pump, the impeller was rather beat up and "dulled down" so to speak. Needless to say, the radiator had to be replaced as well because it had so much buildup in it and about the worse scaling problem i've seen. The usual root problem though is just flat out that the coolant just either isn't flowing fast enough or it's not allowed to dissapate heat well-enough.Michael Yount said:
87GT, since you are up on this stuff.... have you ever used a sacrificial plug (i want to say they are magnesium, but could be totally wrong).....they are supposed to "wear down" rather than other components being worn down or deteorating?
Michael, i still need to ground my system, as i think you have recommended....
Michael, i still need to ground my system, as i think you have recommended....
Hi all,
Sorry for the slow reply..been busy. Michael Yount brings up a good point about the aluminum heads, however the thermal coefficient of expansion difference between aluminum and cast iron is approximately -7 x 10^-6 inches per inch per *F. So the mechanical expansion difference caused by 50*F change is only -350 x 10^-6 inches per inch so I don't think that is a big deal at 242*F vs 195*F.
I will agree that 242*F is a little warmer than I'd like to see.
Don
Sorry for the slow reply..been busy. Michael Yount brings up a good point about the aluminum heads, however the thermal coefficient of expansion difference between aluminum and cast iron is approximately -7 x 10^-6 inches per inch per *F. So the mechanical expansion difference caused by 50*F change is only -350 x 10^-6 inches per inch so I don't think that is a big deal at 242*F vs 195*F.
I will agree that 242*F is a little warmer than I'd like to see.
Don
Michael Yount
Mustang Master
Wonderful numbers Don - but you miss the point. The thermal expansion issues merely point to how much the head moves around relative to the block. We tend to think these things are static - but they aren't. Every heat cycle the gasket has to seal between a block and head that are actually moving around at slightly different rates. The gasket makers helped solve that long ago. The issue is the temperatures at which the metal begins to reach plastic deformation - deformation it doesn't recover from - i.e. - warp. When coolant temps reach 240-250F, you've significantly increased the possibility that you're gonna have hot spots in the cooling passages. In one of those hot spots you may have localized boiling - steam generation as the liquid goes to vapor phase. In the tiny spot that it does that (or spots), the vapor doesn't 'cool' the metal like the liquid does. So you have a small spot in the head that is exposed to combustion temps with no coolant to protect it. Combustion temps can vary up into the 1200-1400F degree range. Aluminum alloys melting points are in that same range - so you can see, it only takes a little localized boiling to potentially cause warpage and gasket sealing problems with aluminum. Manageable if the cooling system is up to par, but problematic if you're not managing temps.
I've never touched one personally but i've heard of others using them on the high power monsters. The basic idea is, as you've basically stated, to have it made out of a material less durable or capable than the main material in the system - much like the way a fusible link works in an electrical system. The only bad thing i've heard about them is that since they are "designed to fail" in the first place, routine checking and replacing is needed every once in a while from what i've heard.HISSIN50 said:
thanks for the info. i too, dont know a lot about how they work (i get the principle, but dont have real world feedback). i have thought about those, but then thought perhaps a cooling system filter might be a good move (different principle, but might help catch debris [since i try to keep the systems in good order anyhow] and no real downside that i know of [as long as the filter is periodically checked]).87'GTstang said:
thanks again!
cardudeusa
Founding Member
Anyone ever use a one of those hand held laser temperature scaners. One of my friends had one at the track lastnight. My autometer gauge said just over 210* we put the temp laser on the thermostat housing and it was 183*. When we put it on the head it was 175*. So which is wrong the gauge or the laser temp gun?
Michael Yount
Mustang Master
Your gauge was responding to a sensor whose tip was inserted in the coolant, so it was trying to measure coolant temp. Unless you have had the gauge and sensor calibrated who knows how accurate they are. The laser hand held was giving you a surface temperature (of the metal in the housing/head) probably based on infrared radiation. And who knows how accurate it is. The analogy would be seeking comparison of an apple to an orange by someone who may or may not be entirely sure what either an apple or an orange looks like. If you want to get a sense for how accurate the gauge/sender are, you'll need to power up the gauge/sensor with 12V and a bunch of jumper clips, and then use a pot of boiling water on a stove with a standard thermometer to check water temps against gauge reading. You can use boiling water and a cube of ice to check the accuracy of the thermometer you're using. Most folks just take it all on faith. I measured as many of my t'stats and temp. switches as I could until my wife ran me out of the kitchen.
If you want to get a sense for how accurate the gauge/sender are, you'll need to power up the gauge/sensor with 12V and a bunch of jumper clips, and then use a pot of boiling water on a stove with a standard thermometer to check water temps against gauge reading. You can use boiling water and a cube of ice to check the accuracy of the thermometer you're using. Most folks just take it all on faith. I measured as many of my t'stats and temp. switches as I could until my wife ran me out of the kitchen.
cardudeusa
Founding Member
cardudeusa,
The problem with IR Temperture guns are that they are calibrated for a specific thermal emissivity and in use various objects have different emissivity. For example a black object vs a white object will give different readings when they are exactly the same temperature. I don't know what the magnatude difference is but it is most likely more than a few degrees.
Don
The problem with IR Temperture guns are that they are calibrated for a specific thermal emissivity and in use various objects have different emissivity. For example a black object vs a white object will give different readings when they are exactly the same temperature. I don't know what the magnatude difference is but it is most likely more than a few degrees.
Don
Michael Yount
Mustang Master
cardudeusa,
The problem with IR Temperture guns are that they are calibrated for a specific thermal emissivity and in use various objects have different emissivity. For example a black object vs a white object will give different readings when they are exactly the same temperature. I don't know what the magnatude difference is but it is most likely more than a few degrees.
Michael,
Good Info. I do get the point and in fact the memory characteristics of aluminum do not change until 392*F has been exceeded. Reference http://msewww.engin.umich.edu/research/groups/ghosh/publications/WFbiaxial/WFbiaxial
I also don't think that this plastic temperature will be reached with an engine operating at 242*F with a well maintained cooling system. This is because aluminum has 2.7 times the thermal conductivity than cast iron which tends to reduce hot spots. This greater thermal conductivity is mainly why we have heating issues with our modified engines.
I do not recommend operating at this high of a temperature (242*F, but I don't think that one excursion to this temperature should damage an otherwise well maintained engine and cooling system even with aluminum heads.
Don
The problem with IR Temperture guns are that they are calibrated for a specific thermal emissivity and in use various objects have different emissivity. For example a black object vs a white object will give different readings when they are exactly the same temperature. I don't know what the magnatude difference is but it is most likely more than a few degrees.
Michael,
Good Info. I do get the point and in fact the memory characteristics of aluminum do not change until 392*F has been exceeded. Reference http://msewww.engin.umich.edu/research/groups/ghosh/publications/WFbiaxial/WFbiaxial
I also don't think that this plastic temperature will be reached with an engine operating at 242*F with a well maintained cooling system. This is because aluminum has 2.7 times the thermal conductivity than cast iron which tends to reduce hot spots. This greater thermal conductivity is mainly why we have heating issues with our modified engines.
I do not recommend operating at this high of a temperature (242*F, but I don't think that one excursion to this temperature should damage an otherwise well maintained engine and cooling system even with aluminum heads.
Don
Michael Yount
Mustang Master
Don - I still see it differently; all the stuff about thermal deformation thresholds for aluminum and thermal conductivity is moot. The problem is that for the aluminum adjacent to a localized steam pocket - there is lot's of heat transfer to the aluminum from the heat source (combustion chamber, exhaust valve) and little heat transfer away from it because liquid coolant isn't present - it's flashed to steam. A coolant temp of 240F-250F isn't a problem; but if that's the temp that the sensor is reading, the odds are increasing that somewhere in the system (likely adjacent to combustion chambers/exhaust valves) localized boiling will occur. It's those hot spots that cause the problems because the safe temp limits of the material get exceeded, and the steam simply can't keep it cool. It's that dynamic that forms the basis of Evans waterless-coolant systems; let's be sure it can't boil until MUCH higher temps, and then higher coolant temps aren't a problem.
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