HAD ISSUES WITH MY WATER TEMP GAUGE WORKING FINE NOW. GOT MY SYSTEM FLUSHED, NOW TEMP READS 190-210 WHEN CRUZIN ON STREETS, TOOK IT ON THE HWY OR WHEN ACCELERATING HARD, THE TEMP REACHES TO 220-230. I THOUGHT IT WOULD BE THE OTHER WAY AROUND, CITY DRIVING SHOULD BRING UP THE TEMP. WATER PUMP WAS REBUILT LAST YEAR, 160 THERM , RAD SEALS ON THE TOP AND BOTH SIDES, OVERFLOW TANK SEEMS TO BE 1/4 FULL WHEN IT COOLS DOWN, RAD LOOKS FAIRLY NEW I GUESS. WHEN OUT FOR A 1/2 HOUR DRIVE, I CHECKED WITH INFARA RED GUN, GAUGE SHOWED 205, TOP RAD HOSE AT OR NEAR THERMOSTATE SHOWED 194 BOTTOM RAD HOSE SHOWED 187, FRONT OF RAD SHOWED 172. WHY IS TEMP INCREASING ON HIGH SPEEDS WHEN MORE AIR IS HITTING RAD. I DO HAVE BOTTOM SPOILER. COULD IT BE A PLUGGED RAD/ DAMAGED RAD, BOTTOM HOSE SEEMS FINE. ANY IDEAS, BRINGING IT IN TOMORROW TO GET IT CHECKED.

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Since your infa red gun shows you to be in the correct operating temperature I might surmise that the radiator is fine. How about the sensor? Could it be the culprit? Is the wire to the sensor okay? Is the interior gauge operating properly? Has the block been flushed on the engine? Could it have some crud in it? Lastly is the fan operating properly?

Sorry about all of the questions.... These are just some of the items that should be eliminated as well. Your temp readings point in a different direction than the radiator.

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If you drove it for a while with a 160 thermostat and the infrared gun showed 205, you have a problem.  My first suspicion is the rebuilt water pump.  Not all rebuilds are equal.  If high speed driving increases temp, the problem is almost certainly not airflow, but rather getting heat from the engine to the airstream.  That could be a dirty cooling system, bad water pump, blocked passages in the radiator, faulty thermostat, anything that hiders transfer of heat from the block to the fins of the radiator.

Larry

OK JC. Now some may disagree, but coming from a 36 year rad man. When you run as low of stat as 160, whats happening is when the water hits 160 the stat opens. So, your water is running constantly through the stat and climbing to whatever the temp it wants to be. The idea of a stat is to allow the block temp to hit 180-195 (preferably for me), transfer into rad,  then the cooler water hits the stat and it closes. This allows the rad to pull the temp down, therefore starting the process over. Now when your bringing up RPM's the water flows through the system a lot faster, therefore not allowing the rad to do its job. Most guy's here run 180. I run 195 and my 350 motor sits right at that temp.

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Terry is rite in his summary.... I missed the 160 thermostat line.... I run the 195 thermostat too and was thinking this was your operating temperature range.

Changing the thermostat is an easy task to see if the temp gauge levels out correctly.

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I missed another test you can do. Look inside you radiator. You may have to drop your water a touch. If its a plugged rad normally you will see a lot of lime buildup around tubes. A partially plugged rad will cause a higher speed overheat due to the engine is working harder.

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I agree with Terry and Larry. A cold temp T-stat lets the water flow to fast and you won't get the heat to transfer. If you said it would over heat at idle then I would suspect CFM's coming from the fan/fan clutch. Driving down the road moves more air then the fan draws so if it is getting warmer you need to make sure the rad is not cloded.

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Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System

I have seen this numerous times on Vettes. One thing to check first is the condition of the radiator hoses, particularly the lower hose. At high rpms/high flow demand, the hose collapes and shuts off the flow. I have not done a search of the archives, but several members had a similar problem. The lower hose turned out to be the problem. It was a problem on my 75 when I first purchased it.

Scott

Good thought Scott, make sure it has the spring inside it when you check it out.

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Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System

HOW DO I KNOW IF BOTTOM HOSE IS DAMAGED. I FEEL THE INNER SPRING, BUT I NOTICED THE SPRING TO BE SMALLER IN SOME SPOTS THAN OTHERS. REGARDING THE THERMOSTATE I KNOW PLENTY OF PEOPLE WHO USE THE 160 WITH NO ISSUES, COULD IT BE MY SENDING UNIT. HAD IT OUT TODAY FOR 45 MIN  INTERIOR GAUGE SHOWED 210, CHECKED WITH THE INFARED TOP HOSE NEAR THERMOSTATE WAS 192, BOTTOM HOSE WAS 182.

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GOING TO BRING IT IN NEXT WEEK, REMOVING RAD, THINKING IT MIGHT BE A PLUGGED RAD RESTRICTING FLOW AT HIGH SPEEDS CAUSING IT TO HEAT UP, CHECKING LOWER HOSE AT SAME TIME. IF I NEED TO REPLACE THE CORE SHOULD I GO FOR A WITH A A/C CORE TO HELP WITH THE HEAT.

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PULLED RAD OUT, 35% OF IT WAS PLUGGED GOT IT RECORED, FLUSHED THE BLOCK, DROVE IT HOME TODAY  GOT STUCK IN TRAFFIC DID NOT REACH OVER 190, TOOK IT ON THE HWY STAYED AT 190-195. THANKS FOR THE HELP,GREAT GROUP OF PEOPLE.

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[QUOTE=my7T1][/QUOTE] Terry, I would like your expert advice on Royal Purple Ice for cooling systems? Here is a link to the product.....thanx:http://store.summitracing.com/partdetail.asp?autofilter=1&part=RPO%2DRP01600&N=700+115&autoview=sku

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OK. First of all I have never heard of this product. Most guy's I know if using any additive at all use Redline Water Wetter. The only time I would recommend this is 1. Some high performance or big blocks need all the help they can get as far as lowering the temp. 2. Race only where anti-freeze isn't used mainly because of track rules. I wish I could tell you more about the results of additives, but I don't have a lot of experience in using it. Here's a site that might help.

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Thanks Terry, That a neat link. I knew that you would know something about the wetting agents.

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[QUOTE=my7T1]

OK. First of all I have never heard of this product. Most guy's I know if using any additive at all use Redline Water Wetter. The only time I would recommend this is 1. Some high performance or big blocks need all the help they can get as far as lowering the temp. 2. Race only where anti-freeze isn't used mainly because of track rules. I wish I could tell you more about the results of additives, but I don't have a lot of experience in using it. Here's a site that might help.

[/QUOTE] Guys you should check out Terry's link.

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JC VETTE 70      you said you do not have your bottom spoiler on. yes it is an important part of your cooling system. during the first three months of 1968 GM had real problems with cooling, the recall and fix was to cut out opening down under to get more air to the engine. the other problem I have seen is bad gaskets around the radiato, if they look bad replace them. also make sure the radiator shroud is as close to the radiator as possible without hitting it. also I have found many over the counter sending units bad.    the only other thing I would add to what all the others had to say is; do you know what your furl air mix is? remember the idle mix is richer than the highway mix. if you think you have this problem start by checking the spark plugs if thay ara almost white insted of light gray look for a good dino shop that has fixed this problem befor.

With a new 160 and a cleaned radiator, new hoses, new water pump, and electric fan kit with 190/170 stat, my temp never exceeds 190.  I did this in anticipation of using my replacement A/C compressor, and having the full comfort of A/C instead of burning alive in traffic on hot summer days.