atltempe

About 5 years ago I bought a Miata for my wife. She'd always wanted a red roadster and I came across a great deal on a relatively low mileage 1990 in the right color with a hard top. Cool, a happy wife and a happy life.

I'd started using my wife's Miata to commute to work since my Jeep had become a more and more dedicated off-roader and never got the best fuel economy to begin with. What a fun little car to drive. It's easy to see why these little beasts are so popular, but it sure seemed as though ours (Ours now, not my wife's) could use a few more beans.

I intimated earlier that I'm a Jeeper and I have lived the Jeep credo of Build, Break, Repeat for years and I fell in to the habit of flogging the little Miata. I beat on it hard enough that I thought it would be a good idea to acquire a spare engine and transmission because I was sure I'd trash the existing items in short order. Nope. It just kept running.

At 233K miles I figured enough was enough. I had the 1.8L with a fresh transmission just sitting and it was time to shove them under the Little Red Racer. Since I was going to do all that work anyway, I may as well boost it a bit, right? I picked up a Voodoo II kit from Flyin' Miata, got that hardware installed, fired it up. Oh Boy! Finally gonna have a little juice to go with that fine handling chassis! Wrong again. Can't keep the SOB cool. Tried this, tried that. No bueno.

That's what lead me to miataturbo.net. I'm in the homework phase of the backside of the project. With all the information available on this site I'm confident I'll work out a fix. Sure would like to meet some locals boys who have been down this road.

hi_im_sean

iTrader: (3)

Im in AJ. I got the crossflow from 949, but have only used it NA, and I dont have AC. The needle never moved on track no matter how hard it was driven in april/may. What radiator is that you have there?

Arca_ex

iTrader: (2)

Heyo.

I'm in Chandler/Gilbert area.

Make sure you have a quality radiator (the CSF unit on 949racing.com is good. I have a 55mm Mishimoto that does the job.)

Make sure coolant is not old and nasty. I like to run one jug of the pink Zerex asian vehicle antifreeze which is 50/50 from O'Reilly then a bottle of water wetter and the rest distilled water. Makes for about a 20/80 antifreeze/water mix which is fine out here.

Make sure your radiator cap and thermostat is in good shape. Might as well buy new ones. They're cheap and only take minutes to replace. I'm using Stant 16psi cap and Stant 180f thermostat.

Make sure front end is ducted well. Undertray seals to the radiator. Try to force all the air to go through the radiator, don't let it get by easily.

Make sure fan shroud is sealed to backside of radiator, this helps with low speed and stop and go traffic.

Consider installing an oil cooler with a 180f oil thermostat. This can help with water temps since it's an additional way to get heat out of the motor.

If still over heating after all that, do some research on coolant reroute kit. Also available at 949racing.

Cheers.

hi_im_sean

iTrader: (3)

I would do a reroute first thing. You can source the parts cheaper if you put the kit together yourself. Myself and others have made our own spacers, there is a group buy for those right now in the for sale section. Kia water neck, blockoff plate, a few other things.

Braineack

iTrader: (62)

Welcome to the site atltempe, thanks for joining up!

atltempe

Hi_im_sean & Arca_ex, thanks for the feedback. I'm not too far from either of you guys. I live out at Ocotillo and Ironwood and own a shop in Tempe. Both you guys know how hot it's been down here for the last few weeks but this car is a daily driver and I need it to work properly no matter what the outside temperatures are.

Here's the set up: 1990 NA, 96 1.8l with power steering and A/C, a 2560 Garret w/intercooler at 8psi (2 washers behind the waste gate), an MSD ignition retarder and the piggyback Voodoo box from Flyin' Miata. No adjustments have been made yet since I haven't been able to keep the engine cool long enough. Cooling is an issue primarily at speed.

BHP equals BTU so I anticipated cooling issues and plugged in a Mishimoto 55mm radiator from the get-go but was still running the stock fans. Just now I'm waiting for a fan assembly from Flyin' Miata. The Mishimoto radiator cap failed immediately. It was rated at 19psi but tested at 4. Installed a Stant 16psi unit. Running about 20/80 propylene glycol to water. Replaced the stock thermostat with one for a 5.7 Chevy, it has about a 60% larger opening at operating temps. I have a good aftermarket under cover and have sealed the top in front of the radiator support at the hood latch but haven't done anything yet to seal the sides of the cooling assembly by the wheel wells. The amount of information on this site is overwhelming so any links to threads that take on this task in particular would be welcome.

I spoke to Flyin' Miata about my issue and asked about the bypass specifically. Their reply was that the bypass would be icing on the cake but, for the limited (by their standards) boost I was running, was unnecessary. Their recommendation was to replace the fans.

hi_im_sean

iTrader: (3)

To me that seems backwards. Fans only help when your sitting still or slow speeds, in theory, doing nothing for you at speed. Perhaps even hindering flow even more if they're not on. And why does matter how much boost youre running? If its over heating, its overheating, assuming everything is in good condition, which youve seemed to make sure of.

IMO a reroute should be done on every miata no matter what, just to "make it right" and get the cylinder temps balanced, even if the car isnt overheating, but thats just me. But never mind that, it does make the cooling system more efficient, I wouldnt call it icing on the cake, although I will concede, it may not be the lowest hanging fruit.

There are many, many examples and how to's for ducting, youll probably find most of it in the race prep section or build threads. It sounds like you are having a hard time getting air to go through the radiator so I would focus on that. You also may want to talk to humming.


Also what temp is the thermostat?

atltempe

Believe me, I hear you. But over the years I've learned to defer to the engineers who built the cars and to the guys who have been there and done that. Since I'm completely new to the turbo Miata thing and the guys at Flyin' Miata aren't I'm willing to take their advise. While there's no doubt that there isn't enough air moving through the cooling assembly and proper ducting will be a huge improvement, Flyin' Miatas' experience is that the car needs the up-graded fans because relatively high pressure forms in the engine bay, preventing cool air from flowing through. My initial thought was that a short deflector could be attached to the trailing edge of the under cover in order to create low pressure under the transmission to draw air through the engine bay but I don't see that anyone has done anything along that line. The option that others have taken, after ducting, is hood louvers, something I'm resisting just now because I like to look of the hood as it is. So, ducting and fans is the current plan.

It's a 180* t'stat. Who's Humming?

Arca_ex

iTrader: (2)

Try going back to a Miata specific thermostat you may have created an issue with the larger Chevy one, some cooling systems are sensitive to having proper restrictions in some areas. I can't remember if the Miata is one that is sensitive to that type of thing but it's worth a shot. I'm using one of the Stant Superstat ones rated for around 180 degrees.

hi_im_sean

iTrader: (3)

Yea, it seems around here the often preferred way to accomplish a low pressure bay is through hood extractors. Fans or daily with holes in hood... fair enough.

180 degreee t stat may be part of your problem, have you tried a 195? MT.net prefers the stant superstat for various reasons.

humming (rob) is another local member on here that has an msm with cooling issues that made his own shroud, he is going to sell them as far as i know.

Edit- Aaron beat me to it

hi_im_sean

iTrader: (3)

sean

Aaron

Robert

atltempe

I believe the thermostats you're thinking of are the units intended for a system with a coolant bypass in the housing that closes the bypass when the t'stat opens. My Miata doesn't have that sort of system so I'm thinking the extra flow can only help, and it seems to have helped a bit, just not enough.

In regard to the OEM t'stat, I wonder what the little regulated opening is intended for.

hi_im_sean

iTrader: (3)

I always thought it was to help get all the air out of the motor

Arca_ex

iTrader: (2)

I know what type of system you're talking about but I've seen people that have had cooling issues still in non-bypass systems that have removed their thermostat.

I think the tiny hole in the stock thermostat is made to open a little sooner than the larger opening so that it lets air out and possibly lessens the shock of mixing cool/hot water when the thermostat initially opens.

For seven dollars and 20 minutes of your time it's worth a shot, and you'll have a thermostat that is proven and known to work in this engine.



When I'm trying to solve problems I go for low hanging fruit first, things that take minimal effort and money, just my two cents though.

Also like Sean said, fans will help in stop and go situations but when you're at speed they make no difference. Seems like you already have decent radiator/cap/coolant so at this point we're down to ducting. Hood vents do help a bit but won't outright solve a bad overheating issue.


When the car is overheating is it just cruising around or are you getting into boost a decent amount? Do you have an aftermarket wideband? It's possible it's running lean/hot, I'm not a fan of the tuning solution that comes with the Voodoo kits.

atltempe

Arca_ex, thanks for the feed back. I'm not running without a t'stat, I replaced the stock item with a piece intended for a 5.7 Chevy in search of more flow. I think you're right about the small regulated opening on the stock t'stat being there to reduce thermal shock in a cold engine. I do have a wideband O2 sensor and gauge as well as a boost gauge.

This little beast overheats on surface street driving and at speed, far worse at speed. Since I haven't yet dialed in the Voodoo box I've been staying out of boost mostly. It has a flat spot like Table Mesa in the mid range from being lean and I don't want to cook my fresh engine. Decent fans for around town and ducting to the freeway. that's the direction I'm headed right now. I'm just trying to figure out the best ducting method.

Arca_ex

iTrader: (2)

Hmm. It's just weird that it's overheating while cruising around. Even with mediocre ducting it shouldn't be able to overheat at freeway speeds. Also more flow in a cooling system doesn't automatically make it better. If the coolant doesn't spend enough time in the radiator it can't shed enough heat, that's why you can overheat without a thermostat. But anyways, I guess you can try all the other stuff first and if that doesn't work, come back to that, I just thought it was something easy to check off the list of possible problems is all.

What is your AFR when you're cruising around? Also do you have it pulling any timing when you're still in vacuum as well?

atltempe

Arca_ex

I haven't driven the car much because of the cooling issue but out of boost, just cruising it runs between 14 & 15. You mentioned "mediocre ducting". How about no ducting at all beyond stock. Ambient temps around here haven't helped much either.

Fun lookin' little race cars you have there!

Arca_ex

iTrader: (2)

Yeah that's what I meant. I have completely stock ducting and only one stock fan installed and can't get the car to go past 205F when it's getting beat on at the track when it's 100 degrees outside. And that was even before the oil cooler. Granted I'm NA and don't have an A/C condenser or intercooler in the way but still, you shouldn't be having issues just cruising around.

Is that ignition box pulling timing while you are in vacuum and causing EGT to skyrocket?

Or it's the ******* thermostat. Seriously it's seven dollars, just change it. No idea why you would put a Chevy thermostat in there in the first place even if it fits in the housing. It's the ONLY thing that stands out as questionable in your parts selection for the cooling system.

atltempe

Now I couldn't tell you if the MSD is retarding the timing when it's not under boost. I know it shouldn't but I have no way to track it with the Voodoo box. I can tell you that adjusting ignition timing seems absolutely normal, nothing odd at all. (I also know that the Voodoo box isn't optimal and future plans call for a stand alone ECM. It hardly matters until I can get temps under control)

I hear you on the t'sat but remember replacing the stock item with the Chevy unit was an attempt to cure an existing problem, one I surmised stemmed from inadequate flow. I have 2 perfectly fine, virtually new stock t'stats sitting right here on my desk, a 180 & a 192, both of which spent a short time in the car. The larger regulator does seem to have helped a bit, delaying the point at which the car begins to cook but not preventing it. That's not to mean that I have decided never to re-install them.

greeenteeee

Quickly skimmed through this I don't think you mentioned what rad but I know you mentioned stock fans and ducting.

My 99 NB was running hot in 105+ ambient temps (130+ ground temps at that point btw).

After a coolant flush, swapping out a working & new 180* T-stat for a 192*, having to add foam insulation to make sure air goes through rad rather than around, and the latest thing was sealing the fans behind the radiator.



This is a bone stock 99, with a stock single row radiator, overheating in 100+ ambient temps (of course this is with AC) but with those things listed, I have been able to keep temps low-- 195-200* and only ever climbs up 205+ if idling OR uphill on the highway (with AC).

I never had issues w an NA in 90+ track day conditions but it didn't have AC and had a 37mm rad. I have coolant reroute to put in from the NA but I wanted to make sure he system is good to go before doing so (& because the NB has so much more crap than my NA did on the pax side of the bay)