loco4rx8

... the engine temp needle starts moving?

OR

... the engine temp needle reaches near halfway point?


I've heard both and I'm looking for a definitive answer. Does anyone know for sure? Obviously, I'm trying to figure out if it's safe to shut down the car if the needle has just started to move. Thanks!

Omicron

Engine is in the process of warming up as the needle starts to move, and is fully warmed up when the temp gauge reaches it's normal position. I've found that once the needle starts to move, it's only about a minute before the engine reaches it's normal operating temp.

Mr M

Correct. The temperature gauge doesn't really start moving until the thermostat opens, which is your first indication that the engine is warmed up.

fxdsconv2000

Correct me if this is wrong.

The temp gauge is for the coolant not the engine right? So this would mean that when the needle reaches mid point (or normal operating temp) that is actualy when the cooling system has reached its neutral point. By neutral point I mean the point that the heat from the engine matches the amount of cooling the radiator can do.

With that said once the needle starts to move the coolant is starting to circulate in the system, so the thermostat has opened to allow the warm coolant into the radiator and move the cold coolant from the radiator into the motor. This would mean the engine is up to temp as the needle starts to move.

Even if the above is 100% accurate I don't shut mine off until the needle is close to the middle.

Nubo

I believe the normal operating temperature of the engine lags somewhat behind the coolant needle. When I've driven vehicles with a true oil-pressure gauge it takes longer for the oil-pressure to reach its final value than it does for the coolant temp to normalize. Keep in mind that coolant is being kept at 180-190 deg F, much cooler than many areas of the engine. The goal of waiting for the engine to be "fully warmed up" is that all of the critical interfaces have reached their normal operating temperatures and dimensions.

This is an unfortunate aspect of having a fake oil-pressure gauge. In its absence I would recommend considering the engine fully warmed only several minutes after the coolant needle has stabilized.

Spin9k

Just to throw another thought out... I've noticed what I call 'heat soak' in the rotary.

It goes like this and is a little more noticeable in the cold:

- if I drive and watch the needle get to 'normal' position, perhaps 3-4 miles and continue a short while, then park... my feeling is the car is not quite 'ready' from a full performance point of view, even though technically 'hot'. The car has a certain hard to define mild hesitation to it - a reluctance to max perofmance - it's just not quite 'perfect feeling'.


Then the car rests 20 minutes to and hour -

-then when I drive again, of course it warms very quickly then, but now the car seems 'looser' and just better, more responsive, smoother. Now the car feel 'perfect'.

I attribute this to a 'heat soak' where all parts of the engine and components are truly HOT vs. just when the guage says hot. I noticed this over and over so I feel to get max performance, this needs to be done first.

Of cource this has nothing to do with shutting down the engine, just a 'warming-up' story.

loco4rx8

Thanks for the replies. Seems like it's safest to let the needle get to the halfway point.

mngpao

That is correct. I think the book says to warm it up for 3 - 5 minutes. It takes mine about 4 min to reach its normal position but I drive it for at least 5 before shutting down.

Gord96BRG

Nope, not even then. The coolant temperature gauge indicates when the coolant has reached operating temperature, which is quite different from when the engine itself has reached operating temperature. Remember, there's a thermostat controlling how much coolant circulates in the engine/radiator circuit. The much more important measure would be when the OIL has reached operating temperature, as that indicates that the metal components of the engine are fully warmed up.

If you've ever driven a car that has both a coolant temperature gauge and an oil temperature gauge (some current Audis for example), you'd have seen that the coolant reached the operating temp about twice as fast as the oil. So, if it takes 5 minutes for the coolant to reach the just-left-of-vertical position, then it takes at least another 5 minutes for the oil to reach operating temperature. Maybe slightly longer on the RX-8, because of the larger volume of oil than average. You can also see this behavior on a vehicle with a real oil pressure gauge, such as an early Miata (90-94). The oil pressure is higher when the engine is cold - and again, it's readily apparent that the engine is NOT warmed up when the coolant temperature shows it's reached the operating temperature, and it takes several minutes longer for the engine oil to actually warm up.

Why is this important? Several reasons - the metals in the engine are not all the same, there's iron, steel, aluminum, and the different metals have different thermal expansion characteristics. Clearances in the engine are designed to be correct when the engine is fully warmed up - when it's not warmed up yet, the clearances can be either too loose or too tight from optimal. Running the engine hard like that can result in increased/premature wear of the metal components. Also, if the oil is not warmed up, then it's thicker, doesn't flow as well as when it's hot, oil pressure can actually be too high (blown seals etc).

To sum up - the coolant temp gauge does not indicate when the engine is warmed up. Once it reaches the normal indication, the engine needs at least another 5 minutes (more when ambient temps are very cold) before the engine is completely warmed up.

Regards,
Gordon

loco4rx8

Thanks Gordon. That's helpful for knowing when you can start revving the engine and driving the car "hard," but for flooding purposes, is it necessary to wait that long? My hunch is that as long as the needle has reached halfway, the car won't flood. Am I way off base?

I mean, I've shut the car down plenty of times when it's just reached halfway (even slightly before) and not flooded it. I'd like to know if I've just been lucky.

rx8daniel

For cold start purposes - I'd say when the idle gets down to around 1200-1300 RPM - the rich mixture required for starting is long gone by then. The few occasions I've moved it short distances (like after my p/t job from a parking space after sitting 5 hours to a pump 30 feet away) I let it run a good two minutes - probably three. Sometimes I'll just get out and do the windows first before pumping while it warms a bit. But as some have said - that's a different value of 'warm' compared to being ready for WOT acceleration - for that - I think about two minutes past when the coolant reaches normal op temp.

Gord96BRG

No, like rx8daniel said. Actually, I'd bet that when the coolant temp gauge needle has moved off the bottom, that it's safe to shut down - I'd say that you don't even need to wait for it to reach halfway to normal op temp.

Regards,
Gordon

loco4rx8

Cool, thanks!

91vert

I can tell when mine reaches normal operating temps when it starts idling like ****......shaking the whole car

Getting the "M" reflash on Thursday....maybe that will help.

rotary-convert

that is what I am putting in my note to the autobody shop so that they don't flood my engine.
had an encounter with a bush and gotta get rid of those scratches

sferrett

I'd echo that statement also. With my other rotaries - the needle starting to move up is good enough for me. This usually takes about one trip around the block.

Typically, though, if I am shutting it off after such a short jaunt I will rev the engine (in neutral) up to 3500 rpms and hold it there for a second then lift throttle and turn off the key as it's coming down in revs. (this is described in the manual also). That's the only time when I do that kind of procedure on shutdown - some folks do it every time but I'm not one of them.

Oh and as for thermostat vs. gauge - on my FC, the needle is at middle ground long before the thermostat opens (and the mechanical gauge moves up from cold) - that usually happens about 2-3 miles into the journey. The FD is the same, except I can tell when it's warmed up fully when the oil pressure gets 'normal', which is about the same amount of time. I doubt the rx8 is any different in that respect and the engine isn't really fully warmed up for 5-8 minutes after you've started it - pity none of the temp/pressure gauges are linear as it would make it easier to know.

Simon.