Crossover Tube and MeterMatches

[Serfma]

What is the design, or purpose, behind the crossover tube?

The reason I ask is because I placed an aftermarket coolant temp sensor where the gauge cluster sending unit is (cold coolant flowing into the radiator) and I'm wondering how much difference in temperature it will be versus cutting the upper radiator hose and placing the sensor there? I currently use my phone with a bluetooth OBD2 scanner to monitor the ECU coolant temps but I'd rather not have to use it anymore.

I've read up on the driver side of the block there is a spot near cylinder 7 - 8 in the cooling jacket that a sensor could be placed, would it be best to instead install it there?

 

[PACIFICGREENSVT]

I would just leave it there. What will you gain from moving it a few degrees?

 

[Serfma]

I would just leave it there. What will you gain from moving it a few degrees?

I was unaware of the difference between temps from the coolant going into the block vs coming out. If it's 10+ off or only a couple. I'm going to be using a MeterMatch to set temps to the temp gauge. If ECU reads 250F but the sending unit is reading 230 then it's an issue imo.

 

[Twisted2]

I could be wrong, but I believe the stock gauge sensor location is one of the hottest points, and probably the best place.

An interesting note, is that my digital autometer gauge, running from the stock sensor location, reads 4 degrees hotter than the PCM sensor reads, on the other side of the crossover. (I replaced the stock 125k PCM sensor, and the two sensors still read 4 degrees apart). Anyhow, personally, I'd leave the sensor there.

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[Twisted2]

By the way, I thought the side of the crossover where the gauge sensor was, was where hot coolant was LEAVING the engine--or at least, that it's on the hot side of the system. I might be confused, but I'm pretty sure that's the side that heats up first, before the thermostat opens--the bypass section. Someone correct me if I'm wrong.

Edit: If the gauge sensor were on the cold side, I don't think you'd get any gauge reading until after the thermostat opened.

What is the design, or purpose, behind the crossover tube?

The reason I ask is because I placed an aftermarket coolant temp sensor where the gauge cluster sending unit is (cold coolant flowing into the radiator) and I'm wondering how much difference in temperature it will be versus cutting the upper radiator hose and placing the sensor there? I currently use my phone with a bluetooth OBD2 scanner to monitor the ECU coolant temps but I'd rather not have to use it anymore.

I've read up on the driver side of the block there is a spot near cylinder 7 - 8 in the cooling jacket that a sensor could be placed, would it be best to instead install it there?

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[Serfma]

By the way, I thought the side of the crossover where the gauge sensor was, was where hot coolant was LEAVING the engine--or at least, that it's on the hot side of the system. I might be confused, but I'm pretty sure that's the side that heats up first, before the thermostat opens--the bypass section. Someone correct me if I'm wrong.


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The ECU / PCM sensor for temp is on the passenger side bank, the gauge cluster sending unit is on the driver side bank, which is right after the t stat.

 

[Twisted2]

Exactly.

The ECU / PCM sensor for temp is on the passenger side bank, the gauge cluster sending unit is on the driver side bank, which is right after the t stat.

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[Twisted2]

I appreciate the info, btw. The part I might be confused about is the direction of coolant flow. My point was, to the OP, that that's the hot side of the system, either way. Would you agree? Thanks again.

The ECU / PCM sensor for temp is on the passenger side bank, the gauge cluster sending unit is on the driver side bank, which is right after the t stat.

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[Serfma]

Exactly.

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Shouldn't that side be cooler since it's where the fresh coolant comes in?

 

[Twisted2]

Now I'm wondering if I understand it wrong. Here's how I thought it worked: The hot coolant comes out of the driver's side crossover, where the gauge sensor is--and the hot coolant flowing through that downtube is what eventually opens the thermostat. When the thermostat is closed, that hot coolant is routed right back into the engine block, through the oil cooler. When it's open, coolant is routed into the bottom inlet of the radiator. Then it travels up the radiator, and cool coolant comes out that top radiator hose, into the passenger side crossover.

This understanding, at the very least, jibes with my observations of which parts of the system heat up first, and then which part is the hottest once the engine is warmed up. I could be missing something though! Maybe someone will chime in.

Edit: Thinking about it more, that doesn't seem quite right--particularly since the passenger's side of the crossover only reads 4 degrees lower than the driver's side, per the sensor readings, and my infrared thermometer.

It may be that hot coolant comes out of both sides of the crossover, but can only flow through the radiator side when the thermostat is open--which would make it so that cool coolant travels into the oil cooler/block, instead of into the passenger side of the crossover. I've never had a clear picture. I wish someone would explain the path. Either way, I still believe the hottest point is where the gauge sensor is mounted--and the best place for it.

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[Serfma]

Now I'm wondering if I understand it wrong. Here's how I thought it worked: The hot coolant comes out of the driver's side crossover, where the gauge sensor is--and the hot coolant flowing through that downtube is what eventually opens the thermostat. When the thermostat is closed, that hot coolant is routed right back into the engine block, through the oil cooler. When it's open, coolant is routed into the bottom inlet of the radiator. Then it travels up the radiator, and cool coolant comes out that top radiator house, into the passenger side crossover.

This understanding jibes with my observations of which parts of the system heat up first, and then which part is the hottest once the engine is warmed up. I could be wrong though! Maybe someone will chime in.

Edit: Thinking about it more, that doesn't seem quite right--particularly since the passenger's side of the crossover only reads 4 degrees lower than the driver's side, per the sensor readings, and my infrared thermometer.

It may be that hot coolant comes out of both sides of the crossover, but can only flow through the radiator side when the thermostat is open--which would make it so that cool coolant travels into the oil cooler/block, instead of into the passenger side of the crossover. I've never had a clear picture. I wish someone would explain the path. Either way, I still believe the hottest point is where the gauge sensor is mounted--and the best place for it.

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Whoa yeah after some Googling from what I've found it looks like I've been entirely wrong this whole time. My MeterMatch was reading that the driver side head was a LOT hotter than the passenger side.

From this diagram I found it looks like hot coolant flows out of both heads through the crossover. lol

 

[Serfma]

An interesting note, is that my digital autometer gauge, running from the stock sensor location, reads 4 degrees hotter than the PCM sensor reads

Just noticed you're also a 96 Cobra.. I wanted to ask what your temps are looking like when you're up to op temps? Assuming your digital temp gauge stays close to your PCM readings. Mix of running around town or 4th/5th gear highway driving? Wanting to compare to my own. Thinking I'm running overall hotter because I never degreed my cams when I did my head gasket (wasn't aware of how bad the DOHCs varied to cam timing because of the tolerances of the cam keyways). I am everything stock besides long tubes.

 

[Twisted2]

Nice! Glad you cleared that up. That mere four degree difference thing was confusing me. Makes sense now.

Whoa yeah after some Googling from what I've found it looks like I've been entirely wrong this whole time. My MeterMatch was reading that the driver side head was a LOT hotter than the passenger side.

View attachment 1708630

From this diagram I found it looks like hot coolant flows out of both heads through the crossover. lol

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[Twisted2]

Good question. Well, with the stock radiator and AC condenser, my motor ran extremely hot. I saw close to 240 degrees before, even driving it gently. It would even run close to 230 on the freeway. Years ago, I swapped out the dense AC condenser, for the newer type. This alone made very little difference. I eventually blew a head gasket, and rebuilt the top end.

Last summer, I put a Mishimoto radiator in it, and now it will not get over 224ish, romping it in savage heat. The one time I got it that hot, it was only because I tricked it into getting hot. It only stayed up there for a few seconds though, and came back down to 215 or so. On the freeway, now, in savage heat, it runs in the 208 to 212 range.

By the way, to me, these are ideal temperatures. I'm not a member of the cooler-the-better crowd. Stock fan settings and thermostat, for me.

Just noticed you're also a 96 Cobra.. I wanted to ask what your temps are looking like when you're up to op temps? Assuming your digital temp gauge stays close to your PCM readings. Mix of running around town or 4th/5th gear highway driving? Wanting to compare to my own. Thinking I'm running overall hotter because I never degreed my cams when I did my head gasket (wasn't aware of how bad the DOHCs varied to cam timing because of the tolerances of the cam keyways). I am everything stock besides long tubes.

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[Serfma]

Good question. Well, with the stock radiator and AC condenser, my motor ran extremely hot. I saw close to 240 degrees before, even driving it gently. It would even run close to 230 on the freeway. Years ago, I swapped out the dense AC condenser, for the newer type. This alone made very little difference. I eventually blew a head gasket, and rebuilt the top end.

Last summer, I put a Mishimoto radiator in it, and now it will not get over 224ish, romping it in savage heat. The one time I got it that hot, it was only because I tricked it into getting hot. It only stayed up there for a few seconds though, and came back down to 215 or so. On the freeway, now, in savage heat, it runs in the 208 to 212 range.

By the way, to me, these are ideal temperatures. I'm not a member of the cooler-the-better crowd. Stock fan settings and thermostat, for me.

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Woo okay, I was worried it was only me. PCM readings is what I've been going by, and I noticed on an out of town drive I was upwards of 220F (though I attribute it now to the fuel pressure regulator vacuum line coming unplugged), steady 216F otherwise. It's been around 90F and I normally sit around 208 - 212 even after a couple pulls. I'm running a mishimoto radiator, and a lincoln mark 8 fan (the version that is 2nd highest CFM) which is only one speed so when PCM calls for low speed fan it's running high speed, which concerned me that I was not seeing cooler numbers. At idle I still see around the 208 range just the same.

I'm running long tubes without a tune (though I have a QuarterHorse at the moment) and I've read that it will really lean you out with the O2's being further away from their stock locations, so I'm thinking it's a combination of that + possibly bad cam timing and both banks fighting each other.

 

[Twisted2]

I wanted to add, these temperatures are per my digital stepper motor Autometer gauge, which as I indicated, reads about 4 degrees hotter than the PCM sensor. So as far as the computer was concerned, you could knock 4 degrees off of each of the temperatures I mentioned.

Nice! Glad you cleared that up. That mere four degree difference thing was confusing me. Makes sense now.

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[Twisted2]

Your temperatures seem reasonable, to me. We could always make the cars run cooler if we wanted, with lower fan-on settings, and a cooler thermostat. Your temperatures sound good to me though.

Woo okay, I was worried it was only me. PCM readings is what I've been going by, and I noticed on an out of town drive I was upwards of 220F (though I attribute it now to the fuel pressure regulator vacuum line coming unplugged), steady 216F otherwise. It's been around 90F and I normally sit around 208 - 212 even after a couple pulls. I'm running a mishimoto radiator, and a lincoln mark 8 fan (the version that is 2nd highest CFM) which is only one speed so when PCM calls for low speed fan it's running high speed, which concerned me that I was not seeing cooler numbers. At idle I still see around the 208 range just the same.

I'm running long tubes without a tune (though I have a QuarterHorse at the moment) and I've read that it will really lean you out with the O2's being further away from their stock locations, so I'm thinking it's a combination of that + possibly bad cam timing and both banks fighting each other.

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