Engine going "cold" during highway driving.

[Zac88]

Been noticing during the cold weather that highway driving lowers my coolant temp under normal opperating temp. I have a mishimoto rad and had no issues with it last winter.

 

could it be a bad thermostat?

[seabass07]

Mine does it as well with the stock wrx radiator. It's because you have a more efficient radiator than you did stock. If I'm coasting and it's cold out, it'll go to almost 1/4 on the gauge.

[rob-2]

It shouldn't be a problem

[Max Capacity]

I'm thinking T'stat, try putting a piece of cardboard in front of the bottom 1/3 of the fins in cold weather.

 

My stock radiator will cool after coasting for a mile or so on a cold morning. But never noticed a issue on the highway when it's in the single digits.

[Brian3676]

If a t stat is doing it job it may be slightly colder but still be really close to normal driving temps. Does not matter how big a radiator you have if the stat is closed its closed

[seabass07]

Need to know how low it goes and under what conditions.

[ibr_adam09]

Mines been doing it ever since I installed a mishimoto t- stat. if It's cool (and I mean about 70 out, rather than 90) and I'm on the highway going 80, temps would go down. I've actually thrown t-stat malfunction code several times when the engine should have been at operating temp.

 

 

I too also have the dual core mishimoto rad.

[Max Capacity]

If a t stat is doing it job it may be slightly colder but still be really close to normal driving temps. Does not matter how big a radiator you have if the stat is closed its closed

 

Ture, but when the car is moving at highway speeds and the outside air temp is cold there may be enough cooling air flow to keep the engine ok.

 

If the t stat is working, putting a block in front of the radiator may help. Big trucks do that in the winter.

[frank_ster]

change the t stat .. the radiator could be the size of texas with a correct t stat and it would stay at correct temperatures.

[iNVAR]

The people saying the Tstat should regulate the engine temperature are correct. Suggest you check the Tstat. Might be stuck open.

[700watts]

if it ain't broke, DON'T FIX IT !!!

[frank_ster]

^ thats for people who wonder ... what happened ?

[seabass07]

That's bad advice without knowing how much its dropping and under what conditions. Don't go tearing apart your cooling system without more info.

[rtbrjason]

I wouldn't want it to be too cold. There are a ton of compensation tables that come in to play based on coolant temp. Most of these tables will be at 0, which is what you want once the car is warmed up.

[seabass07]

So what temp is it dropping to? No one knows, since the OP hasn't checked.

[frank_ster]

the is a cel code for thermostat stuck open i believe..

[JmP6889928]

Make sure and burp the system. If it's not burped and full of coolant, the lack of coolant can cause the gauge to misread (coolant sensor not immersed in coolant) and can actually make it look like it's going down.

 

If that doesn't do it, then change the T-stat.

[Zac88]

Well normal temp is ussualy just under half the gauge.

 

its dropping just a little more now but not as low as 1/4

[frank_ster]

^ so it will get worse when its -20 c

[iNVAR]

pic of the needle. it's supposed to fluctuate just a tiny bit. i don't think mine sits exactly at the middle either.

 

or get your laptop or AP and log the ECT. should be around the 180-200 range depending on conditions. if it's staying in that range, then leave things alone.

[ibr_adam09]

I put an oem stat on. man, I forgot how quickly the engine warms up to operating temps.

[LatentWagen]

I put an oem stat on. man, I forgot how quickly the coolant warms up to operating temps.

 

Fixed it for ya. The engine isn't at truly at "operating temperature" until the oil is fully warmed up. This can take up to 10 minutes, regardless of what the coolant temp guage says. I try to stay out of boost, and definitely no WOT for the first 10 minutes of driving after any cold start.

 

To the OP: I had a similar issue with my WRX (had a Koyo rad and GS T-stat). Turned out to be the thermostat, as most here have rec'd. Hope you get it sorted!

[stuck686]

drive it harder!

[Rad1134]

My 99 Legacy GT does this going down the hills of I-70. Stupid me seized the old engine and I had another put in about a week ago. Freaked me out at first but this is reassuring.

[ras06LGT]

The other week when it was down around -10 F for a few days I noticed that after my drive home from work (25 miles, 20 of them highway) the radiator and lower radiator hose were cold. Temp gauge was at normal operating temp, so the cold air flow over the engine must have been enough to keep the temps in check and prevent the thermostat from needing to send much (if any) of the coolant through the radiator.