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Coolant temps and when should I be concerened.

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I’ve changed to a mix of 25 coolant / 75 water + Watter Wetter because before that I was under certain conditions getting some ECTs I had wished were a little cooler. Max under typical conditions before was ~205F but more typically 202-203. The fan seeemed to be on a lot to keep it so. I was however seeing pretty high ECTs on heat soak specifically at quick fill-ups at the gas station.

Now with the new mix it seems to have had a positive effect as it takes much more acceleration cycles and subsequent idling to even get it to 200 and max seems to be ~201 and that’s much less frequent now. If I drive consevatively now it may never even get hot enough for the fan to come on.

However just as before, sometimes when I do a quick fillup at the gas station, usually coming off the freeway, ECT will be ~201 when I shut off the car but minutes later when I start it again after the quick fill up I’m over 210F and the check engine light is on letting me know of the overheat condition. The fan comes on and after driving 1/4 mile I’m back in the normal zone again.

I do expect pulling up to a gas station off the freeway and immediately shutting it off and not allowing the fan to cool anything is going to keep it hot and that the car is off the coolant isn’t circulating so the ECT sensor that sticks into the water jacket is going to see higher temps.

Just wanted to ask if what I’m seeing here is anything unusual. I had hoped changing the coolant mix and adding Watter Wetter would have helped this situation. It does seem to have had a measurable affect on most other operationg conditions but not this one. Currently I just use the Hondata app in my phone to clear the code and move on. This is the only circumstance where I encounter this and it’s not every time.

Per the factory service manual the thermostat (which is OEM and brand new) is fully open at 194 and normal operating temps are ~198-201.

Also worth noting I’ve done some trickery with the ECU to get the cooling fan to operate more regularly as well now. The factory switch has the fan come on at ~200F and only when the car is stationary. I’ve overridden that in the ECU and have the fan come on at 195 and it will stay on up to 30mph, so for stop-and-go traffic it’s useful. This was a pretty nice feature before the Watter Wetter though now it seems less relevant though still worthwhile.

My options regarding the gas station event that I can think of are:

a) Carry on as I have been

b) Increase the trigger temp in Hondata for the error code to 215F instead of the default 210F it came with. My concern with this is it seems like a bad idea to let it get that hot without a code under normal / non-gas station circumstances.

c) Try bigger radiator if it’s important enough, though the one I’m using should be fine. I’m rnning a dual core half size radiator, which is pretty common. Mishimoto apparently makes a 3 core version and they are the only ones that make it. Seems excessive, and might not make a difference anyway in this particular set of circumstances.

Engine is NA b18c1, 1.1 bar radiator cap, dual core half width radiator.

Other question, aluminum block, aluminum head, open deck configuration, at what temperature does bad things start to happen?

Hello don't be concerned by the temp you are seeing that is very normal, I would be raising the check light another 5-10 deg it will not be an issue at all.

when the engine is running keep the temp under the 210f mark, when it is not running I like to see under 22,

if it is getting higher I would be looking for a way to maybe run the fan a little longer after engine shut down maybe 30 sec or 1 min

Regards Ross

I think you meant under 220f rather than “under 22”.

Regarding running a fan after shut down, a question about that just out of curiosity/learning, wouldn’t that just cool the coolant in the radiator but not really affect the temps in the engine since the coolant would not be circulating?

Even with the coolant pump not running, you will get some natural convection movement of coolant through the engine block/radiator (assuming that the thermostat is open) and having the fans running will assist in the cooling of the coolant in the radiator, this will reduce the volume of coolant in the radiator, drawing coolant out of the engine.

First thing I would do is use a lower temperature thermostat if I were concerned about temperatures - what you're reading and what is at the thermostat may not be the same thing.

Second thing would be to see what the radiator cap relief pressure is, and that it's actually sealing correctly - the higher the pressure the higher the potential boiling point - but higher pressures, if reached, will also add stress to the cooling system components. Assuming the 1.1bar cap is operating correctly, that will lift the boiling point of pure water to ~250 degrees.

Third, see exactly what the spec's are for the "coolant", is it a pre-mix or an "anti-freeze" - these normally raise the boiling point significantly, and figure out what the new nominal boiling point is going to be, to establish an approximate upper limit. Depending on the actual ratios, and the coolant properties, this could be anything from a few degrees to 10, or 15f.

So, depending on your specific circumstances, you could have, in theory, 50f of headroom left. In practice, however, you may be better keeping the engine cooler as, while high temp's increase efficiancy when racing and when the engines are designed for it, they can also introduce other issues with heat soak, chearge heating, increased tendency to pre-ignite/detonate, etc.

I have run an engine deep into the red - 250f+, without coolant loss, in extreme heat but it is certainly NOT recommended! I replaced the radiator with a triple core.

Oh, while checking for this post, I did come across several caveats about mixing 'coolant' with a 'water wetter' as there can be some unfortunate inter-reactions - I would suggest you do some investigation for your particular combination, to check if you may have introduced such an issue.

Hi Gord, do you have any links to the articles about Wetter that you are referring to? I researched it extensively ahead, spoke with Dave from RedLine (the company that makes it) and found only positive stories and it’s pretty commonly used on Honda-Tech. All that said though would be interested to read the other stories and what to look out for.

Sorry, I don't - it was just something that some people reported problems with. It may have been some 'off-brand' product(s) not playing nice - and as you checked with Redline for potential problems and got an all-clear, I expect you don't need to worry about it.

I don't recall, personally, ever using a 'water wetter', as I use anti-freeze products that claim to include wetters in them. If I were using a pure water coolant I would use it, and a corrosion inhibitor if required.

Oh, some race tracks ban, or prefer you don't use, a 'coolant' as they can be much more troublesome to clean up than simple water.