3rd Generation Specific (1993-2002) 1993-2002 Discussion including performance modifications and Technical Support Sections.

Cooling issue? High coolant temps

Old 06-10-19, 04:55 PM
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Cooling issue? High coolant temps

Hey

Did some preliminary tuning last night on my FD and something interesting happened. We tune the car on the road with the laptop hooked up to the Apexi PFC with the adapter. Everything was set and the car ran great. We stopped at a shopping mall for a quick bite to eat. When we left the car in the parking lot the coolant temp was 88 degrees C. We went to the restaurant for about 45 mins and came back to the car. Weirdly the car wouldn't start up and we checked the coolant temp, it was 105 degrees C!!!! Now how is that possible? Or is something drastically wrong with the cooling system - air in the coolant? other issues?

Mods include: Koyo Radiator - stock mounting position, Samco coolant hoses, Stock I/C, stock cooling equipment - overflow bottle, caps, etc...

Cheers
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Old 06-10-19, 05:25 PM
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Have no idea on the no-start, but it seems possible to me that the engine heat could cause the coolant temperature to rise that much with the coolant not circulating for that much time. In warm ambient conditions I know when I park mine after it's thoroughly warmed up, and go back to it after an hour or so, the coolant is still very warm, sometimes even above what it was when I parked it.
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Old 06-10-19, 05:54 PM
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ive seen ~100 and above in mine during the past month after parking and restarting later. Never had an issue starting though. I know the datalogit has some settings and values dealing with water temp.

Last edited by AE_Racer; 06-10-19 at 05:58 PM.
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Old 06-10-19, 07:09 PM
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Thanks a lot. I wonder if there is anyway to prevent that from happening ?

Cheers
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Old 06-11-19, 03:02 AM
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Originally Posted by Trinityevo13 View Post
Thanks a lot. I wonder if there is anyway to prevent that from happening ?

Cheers
after the car heats up the coolant gets very hot , and once the car sits still. the pump is not turning the water,IE,no circulation

its rather normal to see temp rise after shut off. factory prevent this by installing FAN MOD that turns the fans on after shut down IF during ON time it passes a certain temp and triggers the mod. but a poor solution.
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Old 06-11-19, 05:37 AM
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The fan mod may have had very marginal benefit for under hood temps but did nothing for coolant temp because there was no circulation. On my car a wire had to be grounded for it to function...it wasn’t a factory setting. Can’t see MAZDA intended it doing anything for coolant temperature.

I’m with everyone else. I’ll see coolant temps initially rise after shut-down. But not sure if that’s directly related to the no-start. What symptoms would a failing fuel temp sensor give?

Last edited by Sgtblue; 06-11-19 at 06:37 AM.
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Old 06-11-19, 07:48 AM
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Those temps are OK for a heat soak. When you start the car and coolant starts circulating again the temps would drop rapidly.

The no-start is a trickier problem, not sure what's up with that but I don't think it's related to the high coolant temps.

Dale
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Old 06-11-19, 09:37 AM
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Originally Posted by Trinityevo13 View Post
Thanks a lot. I wonder if there is anyway to prevent that from happening ?

Cheers
nope! its simple physics. when its running the coolant is 90c, but the engine and its bits are hotter (turbos are at 300-400c), and when you turn the car off. the cooling system is still cooler than the parts, so the cooling system will still pull heat from the engine.
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Old 06-11-19, 09:41 AM
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Originally Posted by DaleClark View Post
The no-start is a trickier problem, not sure what's up with that but I don't think it's related to the high coolant temps.
Check your compression. Hot start problems sometimes are attributed to that. Pressing your gas pedal to the floor when starting hot may help

My OCD procedure for dealing with heat soak is to open the hood, turn on the A/C (w/o starting the car, this engages the fans), wait for heat soak, turn on car to circulate cooler radiator coolant into the engine. Repeat until temps come down. A much better way would be to install an electric water pump that can circulate the coolant without having to turn on the engine. Is this necessary? Dunno, but i've melted water seals before and don't want to go there if i can avoid it
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Old 06-11-19, 10:15 AM
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IMHO a lot of the coolant seal problems have been from the stock design of the FD. Mazda made the car run HOT - the fan switch wouldn't kick on until 107 deg. C stock and you could easily see that temp driving around. That heat soaks everything, then on top of that you have a pre-cat that absolutely COOKS the under hood of the car. I've been around bone stock FD's and on a summer day when you popped the hood you could just feel waves of heat radiating off and you could barely touch or do anything under the hood since it was so hot.

Remember, FD's drove around for YEARS like this without anyone knowing any better.

On top of that a lot of FD's have been second cars that have sat without as much use and never had coolant changed. Eventually the coolant turns corrosive and starts eating the thin cast iron walls the support the coolant seals.

Keep your temps in the 80's (yes, you will see hotter temps with a hot heat soak, that's OK) and change your coolant once a year with 50/50 antifreeze and distilled water. You'll be good.

Dale
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Old 06-11-19, 10:28 AM
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Originally Posted by DaleClark View Post
...and change your coolant once a year with 50/50 antifreeze and distilled water. You'll be good.

Dale
Use only the old-style green ethylene/glycol antifreeze in the FD. The long life AF used in most recent cars does not work if it is exposed to ANY air in the cooling system - that needs a sealed system, i.e., a pressurized reservoir.
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Old 06-11-19, 11:12 AM
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Originally Posted by TomU View Post
My OCD procedure for dealing with heat soak is to open the hood, turn on the A/C (w/o starting the car, this engages the fans), wait for heat soak, turn on car to circulate cooler radiator coolant into the engine. Repeat until temps come down. A much better way would be to install an electric water pump that can circulate the coolant without having to turn on the engine. Is this necessary? Dunno, but i've melted water seals before and don't want to go there if i can avoid it
i do a similar thing (i don't often open the hood, or restart the car), except i use the turbo timer to run the fans
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Old 06-11-19, 11:39 AM
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Originally Posted by j9fd3s View Post
i do a similar thing (i don't often open the hood, or restart the car), except i use the turbo timer to run the fans
If you don't restart the car, the radiator gets cold and the engine stays hot because the water pump is not running. Opening the hood allows the radiator to cool quicker

I also thought turbo timers keep the car running so oil feed is maintained to the turbos. This generally can be achieved by running the car out of boost for a little while prior to shutting down. Restarting after it's had time to cool also pushes cooler oil through the turbos
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Old 06-11-19, 02:18 PM
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You can use a TT to run the fans - you can shut off the car, turn the key to On without starting, turn on the TT, then take out the key and walk away. The car will be "on" without the engine running and the fans will run until the TT shuts the engine off.

Old oil-cooled turbos greatly benefitted from the turbo timer, the old 300zx's were oil cooled and you could easily cook the bearings with a hot shut down. Water cooled turbos don't have anywhere near this problem, it's a good idea to drive easy the last 5-10 minutes if you're on the street or pop the hood and let it idle if you're at a race environment.

Dale
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Old 06-11-19, 03:48 PM
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Wow, thanks a lot for all the feedback guys, really appreciate it.

Couple things:

1. TomU - Pressing the pedal to the floor did help to get it started. Did a compression test recently and they checked out within spec. I will try to do another one soon
2. I find that letting the fans run for sometime prior to starting helps the hot start. I may have to do that, and wait on the fans to cut out then go to start with some assistance from the gas pedal
3. I am currently looking to invest in a vented bonnet to help get rid of the heat in the engine bay. Considering the Seibon TS style. Only concern is the alternator getting wet if it rains, but I can build an AL plate or something to better help
4. Found that subtracting some fuel thru the PFC helped it to start when temps were in the 100's. This was only some random testing and no concrete evidence to support it as we only tried it once. We tried to add fuel and made things worse.

Would hotter plugs make the problem worse? I use the stock rated plugs for leading and trailing as outlined in the manual.

Thanks for the help guys. As always I truly appreciate it.

Cheers
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Old 06-11-19, 05:52 PM
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You may want to try a colder plug. Running all 9s is common. I have the same situation. Was running 9s, but they seemed to foul. Now Iím having hot start problems. Having a large street port probably doesnít help 🤪

May go back to 9s.
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Old 06-12-19, 05:20 PM
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Originally Posted by TomU View Post
You may want to try a colder plug. Running all 9s is common. I have the same situation. Was running 9s, but they seemed to foul. Now Iím having hot start problems. Having a large street port probably doesnít help 🤪

May go back to 9s.
Thanks TomU. I may give that a try to see how it works out.

Cheers
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Old 06-17-19, 07:51 PM
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don't have an answer for the no start but may be of some help as to ECT. i ran, like most, around 87 C on the street. this was w a 2 inch alu radiator, single turbo setup. i recently swapped in a Mishimoto MMTS-RX7-89 thermostat (68 C 154 F) and the Full Function Engineering pulley kit.

i now run 67 C. initially i didn't believe it so i grabbed my heat gun and checked and sure enough... 150/160. it only confirmed what i experienced when i raised the hood... nothing.

Dale describes 87 C best... "when you popped the hood you could just feel waves of heat radiating off and you could barely touch or do anything under the hood since it was so hot."

while i am sure i would run more temp on track here is a run i recently did at 585 rwhp and you will note the temp is 67C



while spark plug heat range may or may not reduce ECT i guarantee you that a colder plug will reduce "Spark Plug Mountain" and therefore reduce chatter on your rotor housing faces.
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