lexus-is2

On my IS250, last year In the hot summer days in July, a few times I experienced my temperature gauge going above the half way mark then coming back down. I thought it was down to the hot weather 31 or 32 degrees Celsius or so. but never had that issue in the previous 5 years of ownership even during the hot days. Anyway then in August last year on a hot day stuck in the city, then when eventually cleared and hit the open roads the temp gauge went rocketing high. Stopped and coolant was boiling through expansion bottle and I was losing coolant through the expansion bottle.

I took it to a garage who checked it after the car had been siting over the weekend and couldn't replicate the overheating on a road test. So they did a pressure test and diagnosed it to be a broken radiator pressure cap. This was replaced and approx 50% coolant changed.

The car was fine since. Few months ago, I did a complete coolant change and car has nicely been staying below the middle mark. However, today with the weather only 28 degrees Celsius or so outside, I was stuck in very slow moving traffic for about 30-40minutes. Just when I got to the end of the traffic I noticed temp gauge has gone higher than the middle mark (not red) but relatively higher than the middle mark. By this time I reached the end of the traffic so was now cruising on dual carriage at 50mph. I also turned AC off and put the inside heating up a bit with windows opened. The gauge settled back down to below the middle mark.

When i came closer to my destination, got stuck in a little bit of traffic for about 5 minutes but it was moving traffic. I put AC back on but temp didnt go up. Got to my destination and left the car idling for a while and temp was still ok. Held the revs a bit and noticed it went up a bit but back down.

Popped open the hood and coolant level is fine. No signs of any leaks whatsoever. My radiator cap is only 1 year old now.

Not sure if the overheating problem from last year has completely gone. I purchased a new thermostat to change as a preventative measure when I get some time but never got round to doing it.


Radiator Cap is ok as it's only one year old
Coolant Level OK
No Coolant Leaks
Radiator Fan Turning ok
Waterpump Seems OK, no noise and no leaking residue next to water pump
Headgasket - there is no major signs of HG problems either
Thermostat - could it be a possible sticky thermostat?


This only happened today and problem is I probably wont be able to reproduce the problem tomorrow, so diagnosing it becomes a bit tricky.

Would really appreciate anyone suggestions or advice.

Thanks

NYKnick101

Is your fans turning on? A part of keeping your car cool on hot summer days is air circulation. If your fans arent turning on, it could be the reason why your car is going above temperature. If coolant is circulating properly it will never get extremely hot but has nothing to cool it self down with. Check the fuses and relays.

lexus-is2

NYKnick101, sorry forgot to mention yes Fan is also working. I've edited the post to mention that too.

Gville350

iTrader: (10)

Could be a fault where the fans are not kicking on when they're supposed to. Possible coolant temp sensor issue sending faulty readings? See if replacing that thermostat helps any.

Next time, though it's not pleasant, turn on the heat full blast to help with not overheating until you get somewhere safe to check on it.
GL!

lexus-is2

Fan is kicking in, as it was quite hot fan was pretty much on non-stop when I was in slow moving traffic. I dont think its the coolant temp sensor either as when I put heat on full blast it reduced the temp. Since I already have a new thmerostat at hand, I will change that. Question is, when coolant is at operating temperature the thermostat will be open wouldnt it? so if the thermostat is open then coolant should be circulating and hence thermostat shouldnt be the cause. But I am assuming a faulty thermostat may close and open even during hot coolant temp? like in my case if it was thermostat that closed, then it must have opened again when I turned AC off and put heating on and picked up speed.

Also, can someone kindly explain why a broken/damaged radiator pressure cap would have cause overheating last year? from what I understand the purpose of the pressure cap is to pressurize the system to a certain psi, anything over that gets expelled into the overflow bottle. By it pressurizing the system it increases the boiling point. So a faulty cap will just cause coolant to boil but why would the temperature get effected?

Wondering it it's worth changing the waterpump too seeing as im going to drain coolant to change the thermostat.

lexus-is2

An update, today was a degree or so hotter and I got stuck in just as bad traffic as yesterday. When stuck in traffic jams, i turned my AC and heating off and opened windows to allow inside of car to stay cool. The temp gauge stayed exactly where it should be. When I passed traffic jams and hit the highway, i started AC and closed windows. There was a moment when I was cruising at about 55mph with AC on, i noticed the temp gauge went from just below the middle mark (where it always sits) to the middle (maybe a bit over) So I turned off AC and heating and it went back down. After that I got stuck in slow moving traffic for about 25mins and kept AC off and temp gauge stayed where it should be.

When i was in stationary traffic with windows open, I could hear the fan kick in and turn off for a few seconds then turn back on.

So, I am wondering since it seems to be linked to AC, could it be the waterpump? as the AC and waterpump are both driven by the drivebelt and maybe having the AC on is effecting the waterpump which is probably not in good shape? Is there any other signs of a faulty waterpump?

Gville350

iTrader: (10)

Yeah, I think you might be on the right track. But first, replace that thermostat and blurp the cooling system. Air in the system causes all sorts of odd issues. Perhaps when the faulty cap and new fluid was introduced, the system wasn't properly bled of air?

lexus-is2

I dont think theres any air in the system. I bled it all thoroughly when I did a coolant change few months ago. Since I need to drain coolant to change thermostat, and to prevent draining coolant twice i'm wondering if I should change the waterpump too? it's not that expensive and theres a good DIY guide on here. My car is a 2006 RWD and is coming up to 160k miles (not km). I am still on original cooling system components, except the new radiator cap that i had put in last year.

Mike_1GO

iTrader: (2)

to properly bleed the cooling system after thermostat replacement, make sure you use a lisle funnel. replace the water pump too. you run the risk of blowing your head gasket if it keeps inching closer to the red.

lexus-is2

I haven't let it go anywhere near red yet, its just a few mm after middle mark. I'll change the thermostat and waterpump as preventative measures anyway. Only thing I noticed is engine oil level is on low mark. Does low engine oil effect cooling system efficiency? I didn't think it does, i thought it was just for lubricating essential components

Gville350

iTrader: (10)

^Well, as long as the oil level is still in the recommended "range", you're fine. If you do run the oil too low, yes, it will have an effect on the cooling system; but that's not the case here.