...i know this a much discussed topic, but there is a characteristic about these hot running c4s that took me by surprise the other day......i was on a two lane road, traffic ahead of me at about 45 mph, in my corvette, air cond. on, approaching an approx. 8% grade, digital temp readout at 215 deg, ambient air at about 80 deg, when traffic ahead as we start up steeply slows then to about 35 mph. for about 20-30 sec at 30-35, the temp rises from 215 to 231, before speed started to build up again and the grade flattens out to start temp down again. later, i checked oil...good, coolant level good...all the way up to the cap and very, very, green....no paper or blockage in between radiator and a/c, new 180 deg thermostat. right now that is all i can think of, but i was very much concerned that in the space of a few seconds, i was fast running out of room on temp and wondering if i was going to reach that dreaded 260 mark. my question....is this a "normal" occurance under stated conditions, or is this something i need to be watching or have overlooked?

 

My 89 does the exactly the same thing. I'm anxious to see other responses. If I don't run the air at all it peaks out at around 215, but once that air comes on she climbs fast!

 

My 84 does it also,especially in traffic.

 

My '96 did until I plugged all the air gaps on the passenger side of the AC condenser and radiator. It still goes up in a hurry while slow moving, but not quite as high.

 

I know what you guys mean. I have a completely stock 85 except with the 3.07's RPO and the car always seems to run between 210 and 240 even with a new water pump and rad.

My red 85 Z51 which has two fans and the oil cooler and it never gets to 190 barely even at a stop light. I have just got the other front fan working so I believe the answer might be an oil cooler because thats the only difference between my two was the oil cooler.

Food for thought anyways. Wish I had a tranny cooler - thats next.

 

The quick rise was a lack of air flow. Starting the hill at 35 decreases your air flow when you got up to a higher speed the increase in air flow brought the temps down.

Do you have both fans?
Hot climate cars came with both fans. Even with 2 fans C-4's run hot. Your high temps didn't last long enough to do any damage.

There are several ways to make a C-4 run cooler.
Trans cooler, engine oil cooler, after market fan, chip, remote switch for the fan, etc.

Yearly replace your coolant, clean the radiator, and check all belts and hoses, replace the belts and hoses every 5 years.

 

...what is the preferred oil cooler for a c-4?....

 

mine does sort of the same thing. all i do is hit the AC when im sitting or barely moving in traffic and it drops instantly. also, mine does not climb at all while moving. i'm told this is normal, but it is kinda scary.

 

my 85 z51 does the same thing. my particular problem is not related to airflow. i could get to WELL over 200* within 2 minutes, yet the engine was cool to the touch. I found that the problem is that an airpocket forms inside the engine just behind the temp senor for the dash. This sensor is just below the throttle body. That air heats up MUCH faster than coolant does, so you get a false reading. You can remove this sensor and fill the radiator till water flows out the hole, then quickly replace the sensor. I also set up my fan with a switch inside so that if i need the extra cooling power i can flip it on whenever....now under my watchful eye, i never see temps above 215* EVER. So, in your case you could have gotten an airbubble back there and that caused the problem.

Your A/C compressor could have just kicked on too, and that would drive up the temp immediately.

good luck and keep

 

My engine temp hit 250 today in certain areas going up the mountains to the summit enrt to Lake Tahoe. A/C on and the vette did fine. A slight oder of coolant at that temp, but no leaks or problems. Outside temp was around 85. Coming back through Sacramento in stop and go traffic, it hit 250 degrees again with outside temp at 105. Drove in stop and go traffic for about 25min. No problems. I have no blockage of any kind around the radiator. Normal temp for my vette on the hghwy without traffic is when the gauge needle is in the middle btwn the lowest and highest temp. :flag

 

I couldn't have said it better than redwing76. He covered all the points
that I wanted to cover. Good advice.

 

...to 91vetteboy...i am amazed that you were at 250 deg at a sustained period of time.....25 minutes or more........i was not aware that temps could go that high for that long and the engine survive.....even though the magic number is 260.....

 

Did you decide on a solution?

You could have an air pocket.

You might have to siphon out half a quart before you try this for rising glycol.
I usually start my car (must be cold) with the cap off and wait (watch your eyes and paintwork for splash) for the glycol to flow though the core and typically it will rise as pressure builds so be carefull as it can happen fast. If it starts to puke out or gets too high enough to come out just put the cap on quickly - Don't shut the car off before putting the cap on or it will definately puke glycol out. This should usually work to get out air pockets. Let cool and add as necessary for first day of checking to be sure.

Alot of times when the glycol is flushed or replaced, alot of older antifreeze or if flushed with water can remain in the block unless the knock sensor plug(s) are removed which is lower. Sometimes I add a quart of straight glycol to the mix to help adjust the cooling and freezing point ofthe stuff I could not get out on a flush.Always check after with a glycol tester to see how good your antifreeze is.

Mine has to be good for -40 Celcius up here in Canada otherwise it would be a bad day when I get my car out each spring season from the winter.

Remember that the rad cap if 16 PSI is good for 48 degrees appox of extra cooling under pressure as well. Make sure it is also good.

My Oil cooler is still the stock one that comes on Z51 cars that fits between the block and the filter. Maybe you can find one.

I swear thats the diff between my two 85's

Maybe a 160 degree thermo?

Good luck

 

Why is 260 the magic number? The reason im asking is that in city traffic last weekend, the gauge hit up into the 70's and I saw the red light on. I got it checked out and they said they didn't see anything wrong with it, now instead of going up that high it just seems to linger around the 50's. But from what I just read it doesn't look like the 50's is good either. I remember it used to be hanging around 215 but that could be attributed to the fact that it is a lot hotter out now than it was when I remember the 215 mark. Any advice would be appreciated.

 

...well i started this thread to gain information concerning hot running c4s from those that have already been through their experiences with high temps....and from what i read, 260 deg seems to be the highest temps before damage will occur to the engine, heads and head gasket...and then there is duration of that temp as well, plus, as mentioned, where this temp is taken from; where the sending unit is located. i have really appreciated all of those who have offered their insights and expertise, and if there is any more out there, i would welcome it.

 

I have experienced the same problem with my 94. One of the fan relays only worked intermittently. When they both work, the car never gets above 127.
Also, I clean the outside of the radiator about every 6 months. You'll be amazed at the amount of crap you get out of the fins. I use a piece of soft aluminum tubing adapted to a water valve to wash the radiator out by working through the fans. The car always runs about 10 to 20 degrees cooler afterwards.

 

...well i checked at the house after driving in....and both fans are on, with the digital readout at 235-240....later i used a water hose to back flush through the radiator from the fan area, and the water pushed through and it was clean. looking through the shroud opening on the right side, i see no trash or anything on the front of the radiator....the a/c unit is also clear.......2 year old water pump, new thermostat(180 deg), new coolant......all about 2 years ago.....i checked underneath in front and there is an opening very similiar to a big mouth already there allowing frontal air to enter directtly on the a/c radiator........though the engine radiator has to bring air in from underneath right off the surface of the roadway....

 

I've even used a bottle of water wetter & even hosed out the fins from top to bottom. Made no difference.

 

We have a few "hills" here in Nevada and roadside signs warn the motorist to turn off the A/C due to the length of the steep grade. Not fun, but it gets you to the top without boiling over. Personally, I've never had a problem with overheating but I've seen an awful lot of cars parked on the berm with steam billowing out from under the hood.

 

There's an excellent book about how to keep your Corvette cool called "Air Conditioning Stragegies for the 63-82 Corvette." The name is misleading, although it does cover AC. It really covers how to keep air flowing through the radiator instead of around it and keep your car's engine cool. I used all of the stratgies on my '79 and kept it running under 195 degrees even with the AC on. I've applied the theory to a '91 Geo Prizm, a '96 Olds 88 and now on my latest, a '96 CE. It's only $20 and is a good reference book to keep handy. Temperatures here in la regularly top 100 degrees, so I needed a good strategy, and this book supplied it.