Cooling system issues....long..

[TroyV]

Something isn't quite right, and I'm hoping some of you Miata gurus have insight for me.

Here's the scenario. Starting at COM WGI a few weeks ago....

First day...rain/wet track all day. I do four or five sessions. Each time, after I come in, I smell coolant. The rain has water everywhere, but I can see a discoloration on the rad and can tell it is leaking. Not wanting to make the problem worse, I stop by a parts store after the first day and pick up some stop leak. I put it in the morning of the second day. The second day is dry....we are running much harder. I am back and forth with one of the other Miatas in the first session. After about the 30 minute mark and some hard laps I see the temp gauge begin to spike. I back off and putt around to the pit. As I putt around the gauge begins to come down a little.. I run the heat and it comes down more. I come into the garage, and the over flow bottle is bubbling.....and there is evidence that some coolant has exited the over flow tank.

I figured that I may have made the flow less by adding the stop leak. I take the next session off to trouble shoot the problem and determine that the car is fine to run the TT laps. I run the hot laps and I catch the driver ahead of me.....the gauge comes up ...but with the heat blowing full blast.. it is somewhat under control. I come back out for my re-run and the gage comes up in the third lap, but I'm almost done with the TT so I press on.... I come in with the heat on, and the temps return to normal

I get home and swap in a new radiator...nothing fancy...just a stock replacement from NAPA, and a new Tstat.

Fast forward to Summit Point 10 days ago

I'm in the second dry session of the first day.....battling with a sticker laden red Mustang. At about the 20 to 25 minute mark, I see the gauge start to spike again........this was after some very hard laps... I was not running the heat. Just as I noticed the gauge, the red flag came out for another car broken down on the track. I idled with the heat on and it came down. I came in, saw the level down in the over flow, and added water. I ran the car the rest of that day...hard...no issues....including two additional sessions of a buddy of mine who broke his car earlier in the day. I ran the car all day the next day.....10 sessions back to back to back.....only stopping for food and fuel......but the conditions were rainy. There were no issues that day. Add to this that I pulled my tire trailer fully loaded with tires a full cooler, and 20 gallons of fuel 1044 miles round trip for Summit Point ( and 772 miles round trip for WGI ).... no issues up or back either time.

I drained the entire system when I put the new rad in, and have a 75% water 25% coolant mixture in there now. I put in the only T stat the NAPA had at the time which is a 190*......there was a 180* in there previously.

Is it just that I'm not getting enough air through the radiator? The design of the intake doesn't allow me to block very many ports off to "box" the radiator in, but I could certainly block some of them.

or

Did the stop leak make more problems with the flow inside the engine?

Would there be any benefit in running a 160* stat?

Will says he never experienced these symptoms when he had the car, and I believe him. The symptom really only pops up when I have been running very hard laps for extended periods running very close to red line..

[boltonite]

fwiw many sm guys 'core' their thermostat to improve flow (w/o causing cavitation).
You could do a better job of sealing the openings around your radiator, it made a big difference on my car.
Other things I've seen in a spec miata (w/ a working radiator) are head, water pump, and belt issues.
-FF

[TroyV]

Thanks Fred, and thanks for your help at WGI too.

I'm really not looking forward to finding out that it is a head/head gasket or water pump issue....but I do have 23 days before I leave for Tremblant. I'll try the simple solutions first..

[paultg]

Does the car have the plastic under tray installed and the plastic in the front bumper as well? I have read that those help direct the airflow through the radiator as well.

Also, you can wire the fans (your car has two I believe as it had A/C stock) in parallel so they operate together if that hasn't been done yet.

Check these from miata.net garage as well. I know they are more "street car" specific but might find it useful:
http://www.miata.net/garage/waterplug.html
http://www.miata.net/garage/cooling_system.html

[cuda6666]

Thanks Fred, and thanks for your help at WGI too.

I'm really not looking forward to finding out that it is a head/head gasket or water pump issue....but I do have 23 days before I leave for Tremblant. I'll try the simple solutions first..

When dealing with matters of philosphy or what not, checking the simplest issues first makes sense. When preparing a car for an event one month away, I'd say eliminate the potentially serious issues first. If that doesn't pan out, you still have time to do the simple stuff. Rule out a bad head gasket first.

[Crusin]

Have you confirmed the engine is actually overheating? Could the gauge or sensor be defective? Does the engine exhibit signs of being hot like smell or sounds? Have you changed the pressure cap when you installed the new radiator?

[WillM]

Have you changed the pressure cap when you installed the new radiator?

Very good question.

[TroyV]

No....but a new one arrives in the morning.....along with a fresh 180 stat. I'll also install the fresh belts I got, and check the belly pan and other various airflow related items. It's awesome how cheap the parts are for this thing.

To be safe I'll check the rad head space for compression gas.....and when I say I'll check, I mean Rosnick.. If there was a HG problem aside from compression gas in the cooling jacket, I'd figure there'd be more evidence of oil in the coolant, coolant in the oil....or coolant coming out of the tail pipe as white smoke etc... All that stuff checks out all the fluids are perfectly clean, the car blows zero smoke, and runs like a champ.....well.....former champ.

[nhsilversti]

i would guess water pump cavitation issue

[rnoonan]

Don't rule out the head gasket because the fluids look good. I had a similar, though more serious, problem with my MR2. As long as I kept the rpms below 3000, everything was fine; above 3000, the coolant would boil. No oil in the coolant, no coolant in the oil, no nasty smoke from the exhaust - just great clouds of steam from the overflow tank. Problem was a blown head gasket.

-= Rick =-

[TroyV]

The radiator head space chem test should expose that particular failure of the HG.

[offcamber09]

If you bring it when you pick up the BMW- we can check for the exhaust gasses in the cooling system.

Here's hoping we don't have a repeat of the Cobra- although a head gasket job on the Miata is a hell of a lot easier job than the Cobra.

-Scott

[paultg]

Don't rule out the head gasket because the fluids look good. I had a similar, though more serious, problem with my MR2. As long as I kept the rpms below 3000, everything was fine; above 3000, the coolant would boil. No oil in the coolant, no coolant in the oil, no nasty smoke from the exhaust - just great clouds of steam from the overflow tank. Problem was a blown head gasket.

-= Rick =-

Rick, is your MR2 supercharged or Turbo charged? The reason I ask is sometimes depending on the engine design, gasket failure location and/or cylinder pressures you can actually loose a gasket near a water jacket and excess cylinder pressure can force coolant out of the motor (instead of it getting into the combustion chamber). The Subaru boxer engine is known for this type of head gasket failure (even on NA motors); more common on boosted Subarus.

You can actually continue to drive them so long as you keep the RPMS low and wait for parts to show up. Very strange.

Paul G.

[John F]

My daughter's BMW has been doing exactly that and I've been trying to figure why I can't seem to purge the air out of the system. I've been wondering if it was a head gasket, but it shows no obvious signs. Thanks for the insight.

[TroyV]

It is difficult to detect without using the head space chem test. It was almost imperceptible on my Cobra otherwise, but the test exposed it within few seconds. Whoever came up with that was pretty clever.