My B18c1 Civic race car is running very cold when I rev to hig RPM. I can see the temperature going down almost to the C. It was also close to the C at the end of lapping sessions. I tried installing a new thermostat, thinking it was stuck open, but this changed nothing. Any ideas? Could there be a problem with the thermostat housing that's allowing coolant to bypass the closed thermostat?

 

Could be the thermostat. Have you checked the fan-make sure it is not running while at speed ( a test light will confirm this while on track). You make no mention about the size of the radiator or type-is it stock?

 

I swapped the radiator for a full width aluminium Integra unit. I know the problem is not caused by the fan as I didn't even have a fan on the car when the problem first popped up. The thermostat is a brand new oem unit, installed yesterday, and the problem is still there... weird, huh?

 

Are you using anti-freeze or water? If anti-freeze it should be 50/50. If water are you using "Water Wetter." Either of these can cause the temps to change downward if the concentrations are wrong or you mix the 2 (anti-freeze+wetter) together wrong. The rad itself may be part of the issue, but I would doubt it if it is clena inside.

 

Hi Vince. It's Dave, from HADA (the guy with the red hatchback from the TRAC school last weekend). I have suffered fluctuating engine temp readings due to a bad seal at the rad cap and on a separate occasion due to air pockets in the coolant system. In both cases as rpm climbed the engine temp reading would drop towards zero. You may also have a bad ECT sensor at the thermostat housing. I cured the problem in the first case with a new rad cap and in the second case by bleeding the coolant system.

 

Thanks for the advice Dave and others. I already tried changing the rad cap for a borrowed one and it had no effect. I guess I should try to do another bleed and inspect the thermostat housing, then see what happens.

 

When the temp drops, do the radiator and hoses get cool too? When the temp drops like that, try turning on the heat. If you still have heat, the guage is reading wrong. If no heat, you really do have an engine that gets colder the harder you run it and I have no idea how that is possible.

 

Doen't the therostat open on B18c1 at 175 degrees and stay open untill you lower that temp. To let you know Vince i run a dual core rad (1/2 the wideth of the teg tho) and i run lapping events at St.Euastache at around 210 degrees freinent. I don't see even if the thermo is stuck up that you still have almost sub 100 degree F water temp. I would imagine that your water temp sensor is screwed up and the heat from the engine might cause the sensor to give bad voltage readings

 

The temperature is actually dropping, I can tell by turning on the heater that there is less available heat. My mechanic has the car now and he's still baffled.

 

Bump from the dead. What was the fix? I am experiencing the same thing.

At rpm over 5500 the temp drops from 180 to 150 real fast and comes right back when the rpms drop back down. Does it in very gear

 

If you bumped a thread from the dead and there was no fix....
Nobody reported one.
The thread is 8 years old, and I doubt you and this other guy are the only ones to ever have this issue.
There has to be something reported on all this?
Question to you.
Whats your cooling system consist of?
Do you have a larger radiator than a stock civic rad?
I have an integra dual core in mine, sure keeps the temps down.
You might want to change the gauge or the sensor, and see what temps you get from it then.
A 30 degree swing is an awful lot to experience in a short period of time.




Will give you credit for searching though.
Try Googling it or contact a reputable honda mechanic

 

Sounds a bit like a stuck open thermostat... does the car take a long time to warm up?

 

 

Is this for a race car? Do you guys use thermostats on your race cars? Curious...

 

Sensor s accurate, verified by viewing stock ect in head through Crome. When it is warmer out it does not change as much. Stock cooling system, 180 stat, 90% water. Dedicated track/ autox car and street legal joy ride.

Pretty sure it is the thermostat getting pushed open. Going to drill hole on it tomorrow.

 

Yes. Because pressure.

 

<----thermostat user

 

My racecar doesn't but it's a different monster - why I ask.

Can you answer the question about how long it takes to warm up?

 

So no T-stat? But do you at least run some time of restrictor plate so your pump generates water pressure? Without the system being pressurized your boiling point is significantly reduced and if just running straight water (w/ ww) then with no pressure your boiling point is effectively 212f (or thereabouts). That seems dangerous to me because even if you're reading 190F at the sensor he water that passes by the exhaust valve area in the head sees local heat spike that could cause non-pressurized water to boil and cavitate at the local spot. This could lead to detonation in 1 cylinder or a warped head etc etc.

 

Car warms up in 5-10 minutes. I took the stat out and drilled a small hole... Seems to have helped but not 100%

 

Yes there is a restrictor plate in place of the t-stat. It does come in pressure and we have about a 20psi rad cap on the overflow... Different type of motor of course tho. Warped head pfft - cast iron!

 

The symptoms you describe also apply to a very small leaking or cracked head. Allowing engine cylinder pressure to enter into the cooling system and creates pockets of air. Those pockets are why the coolant temps drop so rapidly.

I think that sooner or later you are going to find a much bigger problem than a radiator or thermostat. Speaking from personal experience.

 

Well I just replaced my fresh sleeved block with 1500 miles because the block was cracked due to sleeve job. So really hope that is not the case

 

Damn, in that case I seriously hope I am wrong. Unfortunately the symptoms are pointing right at that situation. My leak was so friggin small it was not showing up on any test we did. But the unmistakable tell tale sign was a slight loss of fluid over time and a sudden drop in coolant temperature while driving. Also, the heater would stop blowing heat. It no was longer receiving a flow of water.

I am far from and expert on any of this. I just read through this thread because the symptoms were so familiar. Hope it is something else.

 

The fact that I have my heater deleted. And ports blocked off on pipe and head instead of looped... Cause extra pressure at t stat?