I just finished up my new engine a couple weeks ago and the car has run flawless until today. I drove several hours in 100* temps in stop n go traffic with no issues at all, coolant temp 195-205, oil temps 230-235, Trans temps 185-190. I stopped off about 30 mins from home to answer some emails in the shade and give the car a break because the engine is new. The hood was popped open and life was golden. I started the car up after waiting 15 mins or so and drove about 2 miles, the temp swung to 260* in a flash, oil temps went to 265*. I pulled over and shut down, open the hood figuring I blew a hose or something but saw nothing. No coolant boiling, no steam, no funny smells, nothing but both of my fans were running wide open. I got back in the car and started it for a few seconds to move coolant through the motor and shut down. I repeated this process 3 or 4 times until my temps cooled to maybe 240*, then jumped out on the road and ran to 70mph to get airflow. The coolant temps dropped rather quick to 190-195* but the oil temps took 5 or more miles to cool down to the 230* range. When I got home I parked it is the garage with the hood open and hoped it was some kind of fluke.

About an hour ago with the car completely cooled down I took it for a drive and everything was fine for 20 miles or so and the temp outside has dropped to the mid eighties. Then I noticed for no rhyme or reason at a light the temps went from 190* to 240* rather quick but not in what I would consider an electrical glitch. As soon as I started driving the temps went back to 195* and all the way home the temps played this game and stayed in the 210-220 range. I know the shop pulled out all the air when they added the coolant, " distiller water, 1gal coolant, 1 pint liquid ice ". The engine has 700 miles on it without any issues at all.

My water tank is full and I have a 165* therm installed, the water pump is also new. My radiator is a Dewitt's, and I have dual Dewitt's fans that are hard wired. The car has a remote B&M trams cooler with fan, and it has a remote oil cooler.

Could this be a sticking thermostat ? Or could the coolant tank cap be causing this strange issue? I would say maybe temp sensor if I did not see the oil temps also shoot up and hear both of my fans running wide open with the car turned off.

This all started after I pulled over to let the car rest after 2 hours in traffic, and it never once got hot while in that traffic.

 

That sounds really strange. Just a wild thought, but maybe your fans aren't running all the time, due to a thermal overload breaker. Can you rig up a gopro to video the fans and try to repeat the problem.

 

 

Can't explain it all but coolant temps will actually rise for a little bit after the engine is shut off as the coolant absorbs the heat from the engine and there is no longer circulation. Turning the engine off to let it cool is not actually letting it cool.

 

I took the coolant reservoir cap off last night and flush it with clean tap water for same time last night to make sure it did not have any trash in it. I have seen these caps get stuck or sticky and they act weird. My Duramax's cap did this a few years back and it kept boiling coolant. I thought I blew a head gasket but it turn out to be a sticking cap. The forum said flush the cap in the sink for a while and sure enough it fixed the problem. I have no idea why this happens or if it is the same thing.

I guess I will pull the thermastat today also unless anyone has anything else to add.

 

I'm having the exact problems as you are. Thermostat changed, dual fans added, coolant changed, compression with leak down performed, fan by-pass switch added and I still have the same heat problems. I've seen water temps as high as 240 on 90 degree days in traffic. Once I'm underway car cools down to normal temps. I'm wondering if the B&M tranny cooler is blocking cool air from radiator. Watching this thread very closely...Hoping someone has the answer....MIKE

 

Not saying this is your problem, had same issue. Head gasket was the culprit. It was a minor compromise but the issue non the less. Keep us posted.

 

In my case...I thought the same. I had a compression test and leak down performed. Everything seemed normal.

 

When it appears there is no end to the rising temps, cycles of short shutdowns that are followed by even shorter restarts, will cool the engine quickly. The water in the radiator dissipates heat far more quickly than in the engine, due to it's larger surface area. A shutdown of two minutes allows water in the radiator time to cool, while the engine stops creating heat. Then a 10 second restart circulates the cooler water into the engine and hotter water into the radiator. Repeating the cycle several times will drop the engine temps a lot faster than just a one time shutdown. That only works when the temps are above the stat rating, but there's no reason to do it unless you're way overheated anyway.

 

This may or may not help, but at least it's different. I was already running warm before I installed my converter and the Vararam was blocking some of the frontal airflow. So I didn't want to increase the load by placing another heat exchanger in front of the radiator/condenser.

I mounted my 70273 B&M cooler horizontally rather than vertical. I took out the 5 screws that hold the bumper cover to the lower front frame crossmember. That allowed the cover to flex down far enough to slip in a portion of the cooler where the center screw was. The remainder of the cooler sticks out to the radiator. Then I put 2 screws on each side back in, which tightened up the opening and secured the cooler. There are no other means of support beyond the clamping described.
Now the airflow to the radiator is not restricted and the airflow to the cooler is the bottom feeder air which runs vertically through the plates. It cools the transmission so well, that it's difficult to get the temps above 150 in our mild Phoenix winter.

Not the best pic and the car is dirty (pretty normal), but this is taken from the bottom side. You can see the depression where the center cover screw is missing.

 

Trust me having the cooler in front of the radiator is your problem! I have run into that issue that is why my coolers are mounted in my front fenders and they draw air throught the brake cooling ducts in the bottom of the fenders and vent in the fender well in front of the tire.

My oil is perfect, no sign of coolant in it and my coolant system does not show any sign of pressurizing . I have a leak down kit, should I perform a leak down? What kind of pressures should I see if everything is fine?

I thought about pulling the therm and testing it first but I don't see how it could be sticking as it is a 165 and it should be 100% open while driving and would have no reason to open or close.

 

The dual fans seem to be a common tie here. If fans stop, temps shoot up high and quickly at low car speeds, but will drop just as quickly when the car speed increases. Fans are not needed above somewhere around 35 MPH. If those fans have a thermostatically activated overload protection, they may be shutting off at high load conditions and turning on again when the circuit cools.

 

I solved the problem by using a MIZAIR Electric water pump.. it runs ALL the time if the engine is running...but when I shut off the engine, I have 2 toggle switches 1 to run the elec. WP. & one to run the Fans...

So at the track when I'm ready to run & start the motor it is about 140 deg.. I do my burn out, and stage, & make my run ..(the WP is running all this time but NOT the FAN!

As soon as I make the turn off, I turn on the fans (manually.. They WILL turn on by themselves if the temp goes over 192...

I pop the hood on the return road, (my engine temp is now about 200 deg... but with the fans running I stop at the time slip booth get my Time ticket, & drive back to my pit spot... (my Temp is now app 190)


I shut off the engine and flip on the two toggle switches (Water pump & fan) and my engine temp is under 150 in 5 - 8 min in 80 deg weather..

I then can shut off the WP & FAN and I wont get "Heat Soak" rise in engine temp...

By doing this I'm ready to make another run at 150 deg in less than 10 min..

That is why I use an "OPTIMA YELLOW TOP Type 34 BATTERY Yes is 10 lb heavier than the OEM, and cost's more but it has been loyal to me for the last 4 years, and that means making maybe 10 runs in one day.. (If I'm lucky & not eliminated 1st or 2nd round )

I have been using the Optima Yellow Top since 2008 with no problems, I should mention that after I'm finished racing I have a 100 mile drive home & that will fully recharge the battery... But To Be SAFE I put the car on a battery tender for 2 - 3 days...

So far, so good...


I'm adding a PS here.. I have a Vararam CAI and I'm sure that blocks a lot of air that would normally go to cool the radiator.. so on any hot day 75 + deg. I run my fans on "LO" speed to keep my engine temp around 180 in traffic... If I'm in traffic (stop & go) and the outside temp is over 85 deg I may put the fan on HI for a few min .. but I NEVER have seen my water temp. go higher than 205 under ANY conditions...

 

This is all good for the track but it is not the ops problem. At the track I can finish a run at 200 and just leave my car with the fans running for 10 min and the temp drops to around 160 very quickly.

As far as crowhater's issue the car should be able to run at normal temps the way it is. I would check that the fans are working properly, that there is no blockage in front of the rad, and lastly the thermostat. It is possible it is defective and closing at times.
I agree that blocking airflow in front of the rad is detrimental to cooling and that is why I also put my trans cooler elsewhere.

 

You are right on the head.. The only things I can think of if the OP has gotten some kind of blockage up between the radiator, & AC condenser... (I had that problem on my C4) or could he have air in the system ? I know having an air bubble can cause the temp to swing crazy...

Just as a point of interest.. on my C6 I bought heavy screen (the type you would put over a window in the shed out back).. it has maybe ((1/8" openings) a very course screen...

I cut a piece the length & width to cover the BOTTOM under the front air dam, & another piece to go directly in-front of the "egg crate" part facing "forward" .. I spray painted them with flat black paint, & used self tapping screws to screw both pieces into place..

Its unbelievable how many times I find leaves OR a McDonald's paper wrapper lodged up against the screen... & I just have to give it a quick wipe with my hand.. & you would never see the screens unless you were LOOKING for them... Total cost under $10 for the screen & can of flat black spray paint....

 

There is no blockage in front of the radiator.

The fans are functioning correct.

I have not checked the therm yet. With a 165* therm if it is not working or hanging up it should do it pretty quick, correct? After driving 20 miles with the temps in the 190 range the therm should be open and it should not be moving any more. I could be wrong and if I am please speak up. By my way of thinking if you are 190-205 degree the therm should not be doing anything it should just be stuck open. The return water from the radiator should be hotter than 160 so why would the therm close at all to restrict the flow. If it was opening and closing constantly to maintain the engine temps at 165 I could see it hanging randomly. Am I just dead wrong?

 

We pulled a vacuum on the system to add the coolant. I also had over 500 miles one the new engine with zero issues before this showed up.

 

this might be a dumb question but could it be the wrong stat, facing the wrong way, in mine with the ewp it has two locations to put plus you have to drill the stat maybe a hose collapsing

 

Why did everything work fine for the first 500 miles? How would I know if a hose is collapsing? What is the drilled hole in the stat for?

 

what water pump do you have, is it hotter out, are you using the air conditioner, i know mine runs hotter with the air on, the hole is so the water can still circulate a little and keep the seal wet in case you turn the pump on and it pumps all the water out of that cavity with the stat fully closed,, are all the lines and hoses hooked the same, if it feels soft or a internal spring in the hose broke. i dont know if the vette has them, just guessing but if a hose got hot kinked or pinched it could be weak, and know the pump sucks and collapses it. under acceleration, try driving with the defroster on high set to 90 and see if it helps, then the cfm of the fans might be the problem or all the above at the same time. or a slightly blown head gasket, it can just blow between cyl and a water port and never mix to rad or oil, I forgot also a bad cat or a bad cam position sensor pulling timing and running lean, i have seen exhaust manifold crack from getting so hot and the water temp went up