aidandj

iTrader: (5)

I agree.

damir130

No, lower relative to the same car running a 94-2000 head gasket (both inc reroute).

chicksdigmiatas

iTrader: (11)

The real bitch is not dropping those copper washers. They have magical properties that make them attracted to places you cant see or reach.

​​​​​​​Wait, yes. The cyl 4 temp would be lower, what we are worried about is what is happening on cyl 1.

patsmx5

iTrader: (16)

Since I doubt anyone has done the exact testing that would be needed to give an answer to your questions, perhaps gathering data on failures and the cooling setups in place at time of the failure would be worthwhile. For example, if everyone without a reroute was nuking #4 stock pistons, while those with a reroute the distribution was random, that would suggest the reroute on those cars fixed a hotspot issue and the reroute had positive real world affects.

chicksdigmiatas

iTrader: (11)

Well, I think one of us needs to man up and do it and acquire the data. Anything less, then we may as well resort to techsalvager style coolant manifolds for guaranteed even coolant distribution.

The problem is, many such as myself are having zero issues, have little motivation to work on their cars, and only tend to do such when something breaks, or the value of the upgrade supercedes our desire to enjoy our car and we believe we would see some tangible benefit from it. Be it improved torque, more reliability, or the unparalleled throttle response we get from datalogging with our sharpie.
When you confound this with possibly adding another unintended issue to fix, such as head removal for a 94-00 gasket. Heads explode.

Tl;dr, we are wondering why we should when we are seeing no issue, and another issue could potentally exist that anyone that has made it through 2 years of engineering school, or just has a general working idea of how water works could spot.

Joe Perez

iTrader: (8)

As a newbie VVT owner, this is the kind of stuff I need to learn.

The FSM, for instance, says that I need to remove the oil pipe from the top of the cam cover, then remove the oil control valve (VVT solenoid), and THEN remove the cam cover as I would on a non-VVT engine. And of course there are a lot of gaskets and O-rings in the mix which are all supposed to be replaced...

Before I went into the hospital, I was about to buy FM's "complete timing belt kit," and I noticed that none of this stuff was included. I emailed Keith Tanner asking about this, and the response was basically (I'm paraphrasing) "Wow, you're right. Never noticed all that stuff wasn't included. I'll update the kit."

So either very few NB2 owners have actually bothered to replace a timing belt, or I'm just totally clueless. Either way doesn't fill me with confidence, and doesn't mesh with Scott's advice that one simply unbolt the hardline at the back of the head and proceed as normal.

This is what I get for being so far behind the curve, and having gone several years without owning a car of any kind, much less a Miata. Lot of catching up to do on the basics...

But I'm getting off track...

Joe Perez

iTrader: (8)

Ok, let me make sure that we're both on the same page here as far as assumptions. If I read you correctly, you're saying the following:


Referring to my image in post #1, you assume two engines, one with a pre-'01 gasket and one with an '01-'05 gasket, both with a rear-therm reroute. And I understand you to be positing that the CLT sensor at the back of the head should read lower on the '01-'05 engine than on the pre-'01 engine? Is this correct?


I don't see why this would be the case. Or why it would matter.

If we assume the total coolant flow (litres / minute) to be a constant, and assume that all other variables (load, radiator design, overall health of engine, etc) are identical, then I'd expect the temperature registered by the CLT sensor to be pretty much the same.

But this misses the point I was trying to make in Post #1. Specifically, that it really doesn't matter what specific value the CLT sensor is reading. What I'm concerned with is how much the temperature varies between the #1 and #4 combustion chambers.

In the early engines, with the stock (front-therm) design, we know that the #4 chamber runs a lot hotter than the #1 chamber. This is well-documented, and makes perfect sense when you visualize the flow of coolant through the engine. We also know that the overall performance of the cooling system is compromised by the fact that we're allowing quite a lot of "cold" coolant to exit the pump, flow straight up through the front of the engine, and then go right out the thermostat into the radiator again, having not passed through the majority of the engine.

Based solely on speculation and analytical thought, I posit that the redesign of the head gasket in the '01-'05 engines essentially solves this problem. I base this both on having poured a lot of neurons into thinking about the design, and also on the assumption that Mazda actually bothered to spend some engineering time analyzing the problem before arriving at this solution which, again, is completely unique to the Miata was was not implemented on any of the various FWD implementations of the same engine.


And thus, I return to the two basic questions:

1. Does the cooling-insufficiency problem which plagued the '90-'00 engines even apply to the '01-'05 engines, and
   
2. Does applying the same "fix" to the '01-'05 engines actually make the situation worse, and create a new problem vis-a-vis a lack of laminar coolant flow around the #1 and #2 combustion chambers?

And I really wish that I had some real-world data to look at here, as opposed to speculation. But nobody on the SEMA-side of our community seems to be asking the same question, and I'm far too cheap and lazy to sacrifice a head to generate this knowledge. All I can say with any degree of certainty is that this '04 I'm driving now, with a totally stock cooling system, doesn't seem to be plagued by the same overheating problems (even with a functional aircon system) that I experienced in my previous NAs (without aircon.) This anecdotal evidence does not specially address the delta-T question, but it does suggest that the issue of overall insufficiency in the cooling system was in fact ameliorated by in the '01 gasket redesign, and this presumption is reinforced by theoretical analysis of the differences in coolant flow through the engines between the two designs.

codrus

You probably want to re-anneal those copper washers before reinstalling them, BTW.

My thoughts on the VVT head gasket issue are:

- If you're running NA, use a good rad (I like the TSE one), ducting, etc, but don't reroute. That's probably good enough.
- If you're running FI, pull the head to swap the gasket for a 99 one, and that makes it really easy to install the reroute without having to wedge your arm between the back of the head and the firewall.

--Ian

Steve Dallas

Well... I have no tangible benefit to offer this thread, but it is timely for me. Perhaps I can supply some data in the near future.

I have an N/A NB2 that I track regularly. The only cooling system mod it has is a Koyo radiator. In up to 95F ambient heat, I have never seen the coolant temp, as measured at cylinder 4, exceed 206F on the track, and I data log every session. That has caused me to conclude that I do not need a re-route, as long as I stay N/A. However, with an eye toward F/I in the future, I just installed the M-Tuned re-route kit. Now, I wonder if I have done more harm than good with that expenditure. (With the transmission still out, I could quickly and easily reverse that situation.) It seems the thing to do is install a temp sensor in the water neck block-off plate and wire it up to the MS for logging.

hector

You likely won't get usable data from putting a sensor on an area with no flow like the block off plate.

And I never studied thermodynamics but it would seem to me that the re-route with the early gasket would be better since you would not be forcing hot water back to the #1 cyl which is already being limited in flow and especially on the intake side. Wasn't there a pic in a thread about JDM (yo!) pistons where it showed the piston missing a chunk at the intake side on cyl1? Will see if memory is correct when I find it. Not empirical data obviously but maybe a sign.

And Joe, running 210-215 in traffic sounds a bit high. Can't remember off the top of my head but I believe I run ~200 in city and at the t-stat opening on the highway. This is an 01 engine in a 95 car with the AC on so both fans pulling air as yours would be. I'd say your rad is shot.

Edit: looks like cyl 1. Like I said, not empirical data, etc. and I have no idea of re-route or not, or the gasket used, or.......

Steve Dallas

I don't remember much about fluid dynamics, but I do remember how unpredictable flow is in many circumstances. The only way to know how much flow is at the front of the head with a re-route installed is to measure it. Who knows what that sensor might see? If the water is stagnant in that location, all the better. Compared to my previous situation, it might tell me something whether a re-route hurts or helps an NB2. Front of the head vs. back of the head data is useful to me in its own right.

Joe Perez

iTrader: (8)

I'm happy to see that I've been able to instill fear, uncertainty and doubt in someone.

But I would love to see instrumentation of the front of the head vs the back of the head under load, preferably after the two (presumably different) sensors had been simultaneously calibrated in a pot of boiling water so that we can differentiate measurement error from actual data.

ME majors, tell me if I'm in the weeds here, but I *think* that this test should give a reasonable indication of the delta-T across the metal of the head casting as well, which is what we *really* care about.

hector

Well I did state "likely" and "usable" but I did not ask what block off plate you were using.

If the block off plate is on the t-stat housing, I would think it would not be usable data. The stagnant water temp change would come by way of convection so I can't imagine it being useful but since you did study this stuff I will defer to you.

Now if the block off plate deletes the t-stat housing, then that would be usable data since it "should" register temp from flowing water since the sensor would be in the coolant port.

Either way, I would do the early head gasket if doing a re-route and could guess that it would be better than the 01-05 gasket with or without a re-route.

Joe Perez

iTrader: (8)

It might tend to bias the results upwards in that location.

But if the coolant temp is higher in that region, we can assume that the head temp is also higher, because second law of thermodynamics.



On the one hand, I know for a fact that the radiator is shot and the system isn't holding pressure. I posted a pic of the leaking coolant a few weeks ago. Got a 949 crossflow radiator sitting in the garage waiting for me to be physically healthy enough to install it.

On the other hand, I'm reporting what's being told to me by a freeware Android app communicating with a $15 Chinese OBD-II adapter reading a 13 year old CLT sensor.

And on the gripping hand, 210-215° is pretty much dead in the middle (well, maybe the upper third) of the normal operating range for a modern-ish engine. It's kind of the whole reason that these cooling systems are pressurized, as opposed to the one in the Ford Model T.

curly

iTrader: (25)

Uh, no. American and European cars, yes. They run at 210-230. Japanese cars, especially older ones, usually run right at thermostat temperature or a little above. So 190-200.

I honestly think the whole reroute question will never be answered. You can never control the ducting, radiator, engine, fans, weather, coolant mix, or driving conditions enough to get accurate results. We found a potential problem, fixed it, and now it's up to the owner of the car to monitor and maintain healthy coolant temperatures.

I've seen rerouted cars over heat due to minor leaks, poor ducting, etc, along with a number of non-rerouted engine.

We have an enduro car that has a SM style air dam, great ducting, and a rerouted 01 engine, with 94-00 head gasket. Obviously no AC, Koyo's older 52mm radiator, and we run distilled water+water wetter. We were concerned recently with ~215 degree coolant temperatures in 90* heat, that's right on the brink of blowing a head gasket, but it survived for 8 hours of racing.

The shop I work at also has a town bicycle type Miata, 94 with a VVT swap. I believe it has the 01-05 head gasket, with no rereroute and a stock radiator that we run coolant in. Manages to survive a small amount of daily driving, and recently survived our track day, where it was driven by a few people all day long in 80+ degree heat.

The point is I don't seem to see any connection, however I do recommend a reroute to anyone who wants to seriously track their Miata.

Steve Dallas

Hopefully that's a typo, and you mean more than 215. Perhaps 255?

Humor me for a moment. As I said upthread, I track my car roughly twice a month in ambient temps up to 95F, and I have no issues with coolant temps. I have the Koyo 36mm radiator with some sealing. Everything else is stock, and I have run straight FL-22 up until now. Highway cruising temps are right at 194F, which leads me to believe the thermostat and sensor are both accurate. Peak coolant temps on track are 205.8F at the back of the head in up to >=90F weather. These data lead me to believe the re-route is unnecessary in a N/A NB2 with a good radiator.

The question in my mind right now is whether the re-route does more harm than good in a car with a 00-05 head gasket. I'm sure it's fine, but is it really any better at all, or even a little worse?

JasonC SBB

I see my name has been invoked in vain.
My solution with my 01 head was to take the 99 gasket and add 4 holes to the gasket in the area near the exhaust valves, with a 1/4" punch. Green circles below, added to Joe's diagram. (With a coolant reroute, of course). My reasoning is turbos run the exhaust valves hot.
Not much data, but after installing the 01 head (with the added gasket holes) the coolant is noticeably cooler than the 99 head under the same street conditions. Something like typically 4-5°C cooler.
The big thread of this discussion is here
https://forum.miata.net/vb/showthread.php?t=350182

I had written these rules:
-----------
The following is true for any block 94-05. (I don't know about the MSM)

Here is the general rule:
The only time an 01 gasket should be used is on an 01 head *with no coolant reroute.*

All other combinations, use a 99 gasket.

Do NOT use an 01 gasket with a 99 head. Doesn't matter if you have a reroute or not.

If you have a reroute and an 01 head, use a 99 gasket. And consider the modification I described for the gasket.

Here's the problem of the 01 gasket on a 99 head:
The (missing) holes in the 01 head gasket, DO NOT (all) line up with the (missing) holes in the 99 head. You will end up with fewer functional coolant holes than either.
---

DNMakinson

iTrader: (3)

In the back of my mind, I was remembering that there was discussion about the holes in the heads changing, as well as the gaskets.

Thanks for re-aquatinting us with the original thread.

chicksdigmiatas

iTrader: (11)

There is a reason i put that in a sticky. Shittons of good info.

Engi-ninja

If I were running this test, I would put thermocouples into the metal of the head itself, not into the coolant. Coolant temp isn't actually what you care about; hotter coolant exiting the head could just mean it's pulled more heat out of the head, which means the head would be cooler, which is what you want. It could also mean that the system overall is much hotter, though, which is not what you want. Cooler coolant temp could mean that a bunch of coolant is bypassing most of the engine and artificially lowering the temperature the sensor is reporting...you get the point. Thermocouples in the head would eliminate this uncertainty.

I think you could get away with just one at either end, since it seems likely that cylinders 1 and 4 will be the extremes of the head temp. However, I'm not sure if it's strictly correct to say that it's the delta T across the head that we care about; what we're interested in is ensuring an equal and adequate amount of coolant is getting to all 4 cylinders, and it so happens that cylinders 1 and 4 seem to be the ones getting shorted in the various coolant strategies. So I would say it's the absolute value of the temps of cylinders 1 and 4 that we care about, not necessarily the difference between them.