SteveF

Ok guys, I've had my FD for a few weeks now, and have started to wonder about temperatures after the engine is turned off.

My car never sees over 210 F (~99 C) when running, even in traffic on a hot day. However, when shut off, the temperatures skyrocket to ~240 F on a hot day. This makes me nervous, and makes me wonder about longevity. I realize the water temp is getting that high due to the fact that it's not circulating, but still wonder if this is normal? Will these temperatures cause premature failure, or am I being a little too **** about my temperatures?

Thanks,
Steve

Rx-7$4$me

Mine gets up there too, and its normal, your car is just heat soaking and the coolant stops flowing and just starts to get hot. IF you leave it, and it says like 220-230 degree's like 10 min later, you'll be suprised when u start the car again the temp will drop to like 180-200 degrees.

If your **** like I am, just leave the hood open when your car is in a safe area so the air can vent out alot better.

DjRannyKan

let your car sit, and started... let it sit for a few and it should cool down (u shouldnt turn it off right away anyways)

Marshall

Steve, I have a hunch you're onto the reason why many cars lose o-rings even when they've never been overheated. Sure its normal, but its a bit too hot for these aluminum housings. I would love for someone to come up with a Meziere or equivalent electric water pump. You could leave it and the fans on for 10 mins after shutdown. I would imagine that with that, and a good aluminum radiator, you could say goodbye to o-ring problems for good.

SteveF

I let it sit for about 2 minutes after running, with fans on, but unless you leave it on for an extended amount of time, it's still going to heat soak, right?

I guess I was just curious if everyone saw the 230-240 degree peak, when the car is heat-soaked after the short cooldown period.

thanks for the responses!

Steve

DjRannyKan

another thing u could do is turn your heat n for those 2 min u leave it sit and it will cool it down.

Marshall

Yup, but even with the fans on after shutdown, you're only cooling the radiator, you'll still get hot spots inside the motor since the coolant is no longer moving.

rynberg

Those temps are way too high. I have never hit temps that high after shutdown -- 230F is about as bad as I've ever seen, usually it's 220F or less.

I try to never shut down my car with the temps above 195F or so.

Also, letting the car sit for a few minutes is rarely a good idea as it heat soaks like crazy doing that. Before I had the PFC, I ran the A/C a bit and drove easy to get the temps down as far as I could before shutting off. Now with the PFC, I don't have to worry about it as the car just doesn't get as hot.

My advice is to either:

a) perform the fan mod
b) install the thermoswitch from a Miata to kick the fans on at lower temps
c) get a PFC so you can control your fans

Also, if you are parking in a safe area, I always pop the hood for a while on a hot day.

brads

I let my car idle for about 15 secs then shut it off...raise the hood and wait about a 45 secs to a minute...then crank it back up and idle for about 15-20 seconds to get all the fluid circulating and turn it off. I never see more than 210 on the Haltech after that. BTW, I have the stock radiator. This is also good to help cool the turbos down.

SteveF

1) I have an upgraded radiator, with miata thermoswitch, and on a HOT day, on HOT blacktop, I'll get the temps close to 180 before I shut off, but the engine is still HOT and heat soaks like crazy. It doesn't seem to matter whether I drive around at 70mph for 10 minutes before I shut down, or stop and go with a short idle before shutdown, the heat soak on this *HOT* day still seems to be bad

2) thermoswitch is installed

3) pop the hood when I park in my garage, and parking safe areas. Of course If I'm in my garage, the air/floor temp is pretty cold, and heat soak isn't as much of an issue in the first place.

Also, what is the peak operating temperature you see? I guess with my peak of 210 F operating, I see a max of 230-240 peak shutdown temp. That's a 20-30 degree F increase for me after shutdown if there are harsh conditions.

thanks for the opinions and keep them coming!
Steve

Rx-7$4$me

See I think everyone is mistaken here. The engine itself really is not getting as hot as the temp gauge shows. At least it doesnt on my car. When my car starts to heat up, it gets around 210 usually no higher, but if I leave it for a bit, and then start the motor up again, the temp immediatly falls down as the coolant flows again, which means the coolan that was inside the motor was actually cooler then the coolant filler neck. So is the motor really getting as hot as theorized?

Rx-7$4$me

I have the fan mod done, and when I shut down the car I get the motor to as low as 175 degree's right before I shut it down. The most I ever see it get up to is like 200-210. My car rarely and I mean RARELY gets hotter then 200 when im driving around.

I have 84 k miles on my original engine and have no signs of o-ring failure.

DjRannyKan

good question i dont know

Marshall

How could it be cooler? The water sits stagnant around the exhaust side and combustion chambers. I think the drop in temp when you start it is from the cooled radiator coolant getting in there.

Rx-7$4$me

There are alot of arguments about the coolant filler neck as being a poor place to have water temp measured. Others have argued it should be somewhere in the block, and I always though it was a good idea to know what the temp was when the coolant flowed OUT of the engine, as it is the peak temp that it reaches while inside the engine. So if my temp gauge drastically drops 10-20 F when I restart my motor, I truely think that the motor isnt as hot as one would think, and that everything above the motor is absorbing the heat of the motor itself. hence why the temp rises.

Of course this only applies to those who have the temp sending unit mounted in the coolant filler neck.

Rx-7$4$me

Yeah thats probably it now that I think about it.

On another note, this has to happen with all cars, I dont think theres really anything u can do but try to get the motor as cool as possible before shut down, and give the hot air the best venting path IE hood open.

SteveF

Exactly, that's the whole problem. The stagnant water in the engine, should be the temperature the engine is at? Therefore if you are at 185-190 at shutdown, then the water guage creeps to 230, it's being affected by heat transfer from the engine.

When you turn the car back on, fresh (aka lower temp) coolant circulates back through the engine.

I just hate the idea of 230 degree coolant sitting in my engine and baking o-rings.

Steve

Rx-7$4$me

well, what I dont understand is if it is sitting stag, then reallly the motor is actually HOTTER then the temp reading at the coolant filler neck is it not? I mean its the hottest area of the engine bay.

So shouldnt the temp go up momentarily when the motor is restarted? or does the coolant flow quick enough that the sender cant display the reading.

SteveF

I'm far from an expert on this matter, so I may be arguing a wrong idea, bear with me

But from what I understand, fresh coolant flows after a restart, causing the temperature to read cool again?

Steve

Rx-7$4$me

Yes, But what I was theorizing was that the motor is actually hotter then the temp reading at the coolant filler neck. anyone have a say about this?

Marshall

You are correct, theoretically you would see an increase in temp for a split second and then the drop. It probably happens too fast to measure though.

adam c

iTrader: (2)

The engine will ALWAYS be hotter than the coolant that is leaving the engine. When the engine is running, the coolant will absorb some of the engine heat, but not all of it. When you shut down the engine, the engine doesn't get hotter. It stops creating heat. What gets hotter is the coolant that is stagnant in the engine. It will heat up to the actual temperature of the engine.

After shutdown, running the fans with the fan mod for 10 minutes (or opening the hood) will keep the hotter components (exhaust & turbos) from heating up anything else under the hood.

rynberg

Steve, I forgot to ask where you were reading the temp from.

Here's my experiences with a Defi water temp sensor mounted in the t-stat housing and the PFC, which reads the stock sensor in the block:

1) The t-stat heat soaks -- BADLY -- after shutdown. I've seen it read as high as 230F, when the PFC is only reading 101C (214 F).

2) The t-stat location reacts much quicker to temp changes than the stock sensor location.

So Steve, I'm not sure I would be worrying about your post shutdown temps. If you are getting the car cool before shutdown and popping the hood, running the fans, etc., you are doing everything you can and the engine probably isn't getting as cooked as it appears.

EDIT: I just went out to my car and checked the shutdown temps after a twenty minute drive in stop-and-go traffic in 80F weather. I shut the car down at 94C (block reading). Opened the hood and left the key in the "on" position -- the PFC turns the fans on after shutdown even earlier than the stock ecu does. The peak reading I got was 100C/212F with the block sensor and 215F on the Defi peak/hold.

RX7 RAGE

iTrader: (22)

What is 105c on the pfc? I've turned my car off when temp was 95c and it skyrocketted to 105c peak when it was just sitting.

pomanferrari

iTrader: (1)

FWIW, VW and Audi use an inline-electric water pump to pump coolant to the heater core. Well, after shutdown, if the water temp rises, the fan kicks in and this inline pump starts circulating coolant.

I've been thinking of doing the same with a used VW pump. Just never got around to doing it.