SimBa

Hi All,

I've been tracking my progress/struggle with this in my build thread but wanted to make a separate thread to hopefully get some more focus on this.

Context
Rebuilt my engine last winter. Details in my signature. Already had a Mishimoto rad, stock fans, added a 949 reroute with the Stant 80 C thermostat (due to previous heat concerns). My car has an aftermarket front bumper ( PO's decision) which did not have the undertray from the mouth to the radiator. I do have the belly pan that goes under the subframe. I am running a water cooled 2560R (no idea how old the turbo is, but it is far from new). I don't know the exact percentage of coolant vs water in my system, but it is more water than coolant.

I did delete the water neck. I have the stock throttle body which is connected to the coolant line on the turbo. The other side of the turbo is going to the mixing manifold. I retained the oil donut as well, which is also part of the coolant path.

I have made some ducting and sealed my radiator. I have my fans kicking on staggered at 85 C and 90 C. These changes seem to have helped, but not fixed my issue.

Issue
I see pretty dramatic coolant temperature spikes. The first day of autocross this season I saw temps spike up to 110 C on a fairly cool day (Maybe 50-60 F?). Since then, I've got the funnel, bled the system more thoroughly, added the ducting I mentioned above, sealed the sides of the rad. Depending on how heat soaked the engine bay is I am usually cruising and idling between 80-90 C with ambient temps between 10-25 C (50-75 F).

The main reason I think something is wrong is the dramatic drop in temps as soon as I get off the throttle. For example, in the photo below, I see a 13 C drop in 1 second. The sensor is located at the back of the head in the reroute housing. This is the standard setup for the 949 reroute.

FWIW this datalog was taken over bluetooth. I'm not sure if that effects the sampling rate of the data.



The research I have done makes me think that the spike in temperatures is expected with the turbo. It seems strange to me that the coolant would drop so dramatically. It seems like there is an issue with flow and when the throttle is released the coolant begins to circulate again, causing the drop. The only hose that I didn't replace when doing the engine swap was the lower rad hose, which looked to be in decent shape and was clear of obstructions (IDK why that's where I decided to try to save money, but it is what it is).

Interested to hear thoughts/feedback on if this is expected/normal behavior. I did check the thermostat before putting it in the engine. For the time being I would rather turn the boost down and live with it as is than pull the reroute housing off to replace the thermostat or drill out a hole.

Ted75zcar

iTrader: (2)

This is what I see on my car and have seen on others like it. To me it makes sense, you are adding a significant amount of heat energy to the water (on the order of 30% total power). When you lift off the throttle you are immediately reducing the energy added. Based on other data I have looked at for exactly this, non-reroute cars don't have nearly as dramatic a drop, which also makes sense, as the flow through the back of the head is much slower and the engine stores more of the heat as opposed to quickly shedding it. Basically a low pass filter in circuit theory or an integrator in math.

I thought about this quite a bit several years ago. I always wanted to measure the temperature of the water entering the engine, but never got around to it.

Nothing factual here, hypothesis only.

I think FM may have published something that correlates with this theory as part of their marketing materials in support of their reroute topology.

SimBa

Thanks Ted. Pretty sure I red a similar reply from you on another thread on this topic.

I'll have to search for that FM article.

I'm not too worried about it if it is normal-ish behavior. If that's the case then maybe hood vents will be added to the list.
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curly

iTrader: (25)

Are you sure you don’t have any aftermarket wiring, especially grounded to the chassis that should be ECU?

SimBa

@curly Are you referring to wiring specific to the cooling system or wiring in general? I do have 3 aftermarket gauges (AFR, Oil Pressure, Knock) grounded to the chassis in the cabin near the pedal box.

Since reinstalling the engine I have gone back and cleaned up/checked the grounds around the engine bay, as I was getting more noise on my TPS than before.

EDIT : The ECU is grounded through the stock harness. I assume this runs out to the grounding point on the IM, but need to do more research.

curly

iTrader: (25)

I’m not sure if it matters if it’s coolant sensor or not, but sensor grounds need to return to the ECU. I know on 1.6s, they ground the coolant sensor on the engine and the ECU. Full throttle pulls do exactly what you’ve logged, increase with RPM and drop off about as quick as you can release the throttle. Remove the chassis ground, and they act normally.

SimBa

I feel like I've seen similar behavior to this as well from at least one other sensor on the car, but can't remember which right now. It's hard to distinguish what might be caused by noise vs what's caused just due to the increasing RPM.

That is an interesting point about the chassis ground I will have to do more research and dig into the wiring harness on the NB1's to see what/where the grounding situation is. It would take all of 15 minutes for me to run some 12 gauge from the IM ground to where I've got a few, working, but slightly lazy, grounds in the cabin.

I realize that's not the same as what you're saying about the 1.6's, but I'm thinking it might help the ECU and gauges be more consistent.

The SpeedyEFI board has a cluster of ground pins, but I'd also need to double check that those aren't used for something else.

m1yeh

+1 probably normal behavior. My observations match up with the description above for a non-route. Same behavior smaller slower change.
I thought it was my safe retarded timing running hot, glad to learn its normal.

Padlock

Based on a lot of my experience in OEM cooling system design, it seems highly unlikely for a 13C/sec temp change rate to be real in the way that you have shown. I would be fairly suspicious of it being measurement error in either sensor placement or wiring. Water's specific heat is about 4x higher than aluminum and 10x higher than steel, which means it is slower to respond to changes in temperature by about that factor of time compared to those materials. Heat is generated from fuel consumption/burn, so if you had a fully instrumented powertrain, you'd see fuel enrichment occur, EGT's rise, head and crankcase temps rise because of EGT and combustion in cylinders, then coolant temp follow last because head and crankcase metals are getting hotter... On the flip side, coolant will also be the last to cool down, so seeing it immediately drop after letting off WOT seems suspicious to say the least.

m1yeh

What is your CLT smoothing lag factor set at?

Ted75zcar

iTrader: (2)

I am genuinely curious about this topic, as I don't remember ever reaching a confident position.

@curly you must have logs on 300whp builds that have reroute. Would be great to see something from the street as opposed to the rollers if possible, as the time durations are usually different.

@Padlock. Maybe you are the one who can provide clarity, but I am not sure the 13C/sec observation is correct. Water is moving through the engine at this point, so the heated water is presumably being moved to the radiator, not that the temperature of the water is dropping.

I have an electronics background, so my knowledge of thermo/fluids is pedestrian at best. The google machine tells me that for a 300whp vehicle, assuming 33/33/33% split of the energy produced we have 300whp worth of energy going into the cooling system, or on the order of 200,000 watts. Now we are in a space I am familiar with, and 200000 watts is enough to heat a substantial electronic load by 10C at these time durations. Conservation of energy is a thing, so either this power is being stored in the metal, or it is going into the water, or a combination of both.

I also believe that a 10s of C drop in temperature across the radiator is common, so we know that we are in the ballpark here. Once again, I never instrumented the radiator outlet, so this isn't known to me, just hypothesis.

kep

I know my car has exactly this grounding issue, as I was seeing some weird CLT signal noise last year. Is this one of the ground rings on the back of the intake manifold?

curly

iTrader: (25)

Here's a quick example, this is an STS miata, so still uses the AFM, and they're not allowed to modify anything as far as I'm aware. CLT in red, MAT in yellow, you can see the drop from 214 to 198 right when I lift off the TPS. That's not water temp dropping 16 degrees in less than a second, water doesn't do that. I found another log where I did a 2-5th blast in another car, and coolant peaked 20 seconds after I returned to idle, held there for 6 seconds, and dropped back down to normal operating temp within 30 seconds. That's typical.

Ted75zcar

iTrader: (2)

@curly lol, hate to be direct do appreciate your reply

Do you have a single example log for a 300whp car with reroute that doesn't exhibit this temperature drop.

curly

iTrader: (25)

No, I have probably hundreds of them though.

Here's two of them, you can see coolant starts to creep up after the run. Keep in mind that dyno runs are even worse than street pulls. I start at 1500rpm and go until it hits the limiter. That's a 35-125mph pull, with a shitty fan in the front, nothing like what you'd actually experience going 100+ on the road.

SimBa

@m1yeh I'm guessing that's a Megasquirt setting, but I did go back and I do have some filtering going on with the coolant sensor. It is set at 50 % (127/255). I'll set that to 0 and see what things look like. I assume they will show the same behavior, just noisier.

@curly I'm surprised those graphs are so linear. I don't believe I've ever seen traces like that even before the turbo/reroute (I also had a sticky thermostat, so maybe not surprising).

Personally I would expect the drop to be much less severe. It seems like a small drop when getting off throttle would make sense, as there's a lot less heat being generated, but I would think there would be a relatively slow taper down to thermostat temp as the coolant flowed and pulled heat out of the head/block.
If the coolant system was capable of dropping 13C in 1 second I would think that either the engine was generating an ungodly amount of heat under load or that the coolant wasn't flowing under load and began flowing again when off throttle.

@emilio700 Do you have any input on this? Have any other customer's chimed in with similar experience? I don't think this is related to the reroute, but it is a big part of the system and houses the sensor.

SimBa

Also, full disclosure, I did break part of the plastic plug on the coolant sensor. I do not believe that this is at play here. The sensor still plugs in solidly and I do have a bit of tape wrapped around it. I've never had an issue with it disconnecting while setup like this.

curly

iTrader: (25)

You’re assuming the temperature logged is actual, what myself and others are saying is that it has nothing to do with reroutes and temperature, but everything to do with ground offsets.

boil a pot of water, then turn the stove off. You can’t touch it immediately, or even 30 seconds later. Same conditions here, the radiator doesn’t sink that much heat, and even if it did, the sensor wouldn’t report it that quickly.

Ted75zcar

iTrader: (2)

Ahh, but see that is the rub. I may not be strong at thermo, but I am very strong with EE, and actually have IP on noise reduction tech for noise introduced through grounding issues. From what I have seen, the temperature rise is either directly or falsely correlated with power. In other words, you don't see it when running the engine speed to high RPM at say 70kpa manifold absolute. Electrically, 300hp and 70hp in this scenario are nearly equivalent. Now there are some esoteric phenomenon (adc input charge transfer resulting in channel bleed) that may very well be in play here.

The pot of water example is not appropriate IMO. Water is absolutely gushing through the motor at that speed. The water measured at t + 1 second is not the same water measured at t. Water temperature is not homogeneous.

It is explicitly the reroute that I am proposing as the source of this being observable due to the above flow.

I wish I had that FM report, because if memory serves it clearly showed a substantial effect on measured temperature from the turbo water feed alone. I do know Mike, I may reach out to him to ask his opinion.

Edit: those plots above are exactly what I have seen and would expect from a non-reroute car. Did that car have a reroute?

SimBa

@curly (Edit : I'm not sure that response was targeted to me) I probably wasn't clear with my last response, but I am in the same boat, I don't think it makes sense to see that dramatic of a drop. I would expect the block/head to take the heat from the cylinders and the coolant to pull it out relatively slowly and linearly. The reason I called out Emilio was because I figured others would have installed the reroute and then paid closer attention to coolant temps and noticed something similar. Not caused by the reroute, but noticed after the install because people were paying closer attention.

I did follow up on the grounding idea a bit yesterday. The SpeedyEFI guys gave me some information about some of the ground wires on the ECU that are good/bad to use for sensor grounds.
I am still thinking through that and doing research, trying to figure out what my options are and which ones make sense. Keep in mind that the coolant sensor is still using the stock harness.

I have noted that my TPS was noisier after the engine was reinstalled, which shares the same ground pin on the ECU as the coolant sensor and a few other sensors. This was why I went back and recleaned my grounds after getting the engine back in.