The sender bad?
Test by heating it up and doing ohm tests at different temperatures.

 

Could be compression getting into the coolant system.
Also, I just ran a temporary wire in my 87 SS driver side head for gauge on dash. It goes way up too but the other (proflo4 sender in intake) stays the same at 185.
My theory is that the little wire may be getting super hot by the header, or even touching/grounding out and causing erratic readings when in reality everything is ok.
In my other car the aftermarket temperature gauge is all one piece from gauge to sender, and works out on a bench with just a butane lighter and no outside power source. It just reads the heat. There are no fluctuations on that one.

 

It could be a sticking thermostat. When you stopped on the side of the road it opened.
Just a thought.
Greg

 

Had the weirdest thing happen today... '68 Camaro, SBC, electric fans, temp gauge sensor is in the drivers side head

Running down the highway at a constant 2500 RPM and 80 MPH for about 10 minutes. Very light part throttle. Dead consistent on the speed for a long time. I looked down and noticed that the temp was at 230. It usually runs around 180 degrees on the highway. I kept my foot in it (part throttle) for another minute or two and stayed at 80 MPH... the temp creeped up to 240. Then I dropped it into neutral and coasted in idle. After about 15 seconds the temp dropped from 240 to 180 over a period of about 5 seconds. It just dropped pretty much immediately. Then the car ran like normal the rest of the drive home.

What might have caused that?

Thanks!

do you have a high volume water pump? could be you are circulating the water too fast through the radiator not giving it time to dissipate. had a similar problem running 212 degrees, using high volume water pump with stock diameter water pump on sbc. switched to a bigger pulley making it 1:1 with the crank to slow it down an fixed the issue.

 

That ain't how it works on a closed loop system. It's common to think that but it's wrong.

 

either airflow restriction or t-stat closed. Your elect fans are useless at highway speeds so that's a mute point. First time this ever happened? is something new? recently replaced?

 

tstat stuck or airlocked

 

ssanto

Likely the 'stat stuck. The drop in rpm and water head pressure just happened to be the thing that shocked it loose.

 

I've always wondered about the information on high volume water pumps and operating temperature experiences people report. I always thought any problem that went away with a standard volume pump would have to be either due to cavitation (for obvious reasons) or the radiator being on the smaller side. If the radiator was smaller, I could see how coolant could get through quicker. If anyone has experience there, I would be curious about the set up. I don't know for sure if my logic applies, I'm just tossing out ideas.

Air getting around the radiator, a "cookie sheet" style fan shroud or the electric fans blocking air flow at highway speeds are somewhat common culprits. If the coolant temp going up isn't a constant thing and this is a one time thing driving at speed, it points to the idea of the thermostat sticking.

Coasting in neutral at 80 MPH, may or may not be a huge deal...but, having the output shaft "in charge" of how fast the direct drum is spinning isn't ideal. It allows for the for the direct drum to "free wheel" and possibly exceed a safe limit for how fast it can spin. I would opt for keeping it in gear and slowing down to reduce the RPM. Coasting in Drive keeps the input shaft "in charge" and the drum can't spin too fast. If you hit the drag strip with this car, shifting into neutral when passing the finish line is VERY risky for the same reason. The output shaft is turning much faster, in that scenario, than it would be at 80 MPH and it's why the risk would be much higher.

 

oval track racers have latched onto double and triple pass radiators lately, a guy that tests these things told me it increases cooling system heat rejection by about 6-8% for the same size core, so speeding up the coolant and making run through the core twice does in fact make it reject more heat

 

More rows of tube are known for blocking adequate airflow , as well .

 

Thermal dynamic science
Laminer water flow does not have the same ability to transfer heat due to a boundary layer between the inner part of the water and the material it's passing by.
Turbulent water will cool better. Moving water faster, up to the point the pump cavitates, will always work better.

2 and 3 passes work because the tubes are often smaller, there for make the water more turbulent. There is way too much monkey see monkey do guys are the track. What they don't know, is all the "tricks" are just compensating for the real problem of lack of water flow or lack of air flow. 2 blades. 3 blades, 6 blades, 20 blades, turbines, hell, it's all crap and cost a ton of money too. $300 for a plastic fan? For real?
Non one running the top MLRA, Cash Money, Lucas or WoO, Dirtcar, USMTS, etc... is doing that non sense and they all have 850-900 8500rpm engine running lap after lap all night long all summer long.

Read this....Follow it....It's really this simple.

Tech Tips - Stewart Components

Guide to High Performance Cooling Systems The information contained in this section is based on Stewart’s 25+ years of experience in the high performance cooling system industry. While few truths are absolute, the following guidelines apply to virtually any application and should be followed as...

www.stewartcomponents.com

 

I haven’t seen any usable temperature drop with multi-pass cores unless the multi pass has more core area than the single pass it replaced.

A similar experience with high flow pumps and high flow thermostats. What I find here is in cold weather the engine runs cooler often under under thermostat temp but in hot weather no noticeable difference. Here flow is limited by the greatest restriction you can’t speed the flow beyond whatever that point is. So just putting in high flow devices without knowing what the physical limit is constitutes guess work at best. Some people get a positive result same don’t, so there isn’t as patent an answer as advertising might suggest.

Water wetter I find is somewhat effective when running water only as coolant but that drops quickly as glycol based coolants are introduced. Problem here is water alone is quite corrosive so any gain is quickly lost to a rust layer.

The greatest heat transfer occurs when the difference between the working fluids is at its highest. In this case high coolant temp to low air temp. This is where the thermostat comes in to balance the coolant flow of temperature into the radiator tubes against the air flow through the fins removing that temperature. Obviously there are limits at both ends of these functions.

At low driving speeds fans are needed to pull air through the radiator. This increases the number of air molecules passing the fins in any period of time so the amount of heat removal increases. Essentially this is where your liquid cooled engine gets air cooled. At highway speeds the ram air into the radiator is greater than the fan air flow so dropping the fan off is useful both from a power loss standpoint and for air flow

A shroud is intended to allow the fan to created a pressure drop across the entire face area of the core so all that area is transferring heat rather than an circumference on the radiator just in front of the fan without a shroud. Obviously the more streamline the shroud the better this works but space imposes limits, very few of us are hot rodding a 1972 Pontiac Grand Prix so sometimes a cookie pan is as good as it’s going to get.

An interesting thing from back when NASCAR stock cars were built from manufacturer stock cars available to the public a common thing done was to reduce the coolant pump flow by slowing it down by juggling pulley ratios and grinding down the vanes to even removing some because the stock pump delivered too much flow. But of course the speeds being attained and held for long periods of time were considerably higher than street speeds. But it does point in a direction that hints that more flow is not an unconstrained answer.

Keep in ind that the factory cooling system is designed around a 50/50 mix of water to glycol so when new at least if pure water was used the system would sustain higher heat inputs like distance racing without needing resizing. The cost is corrosion which over time reduces heat transfer.

Bogie

 

Check the connection to the sender. If the wire is bare and/or touching the head or another part it will send a false reading. When you let off, the wire likely moved enough to stop making contact.

 

Had the weirdest thing happen today... '68 Camaro, SBC, electric fans, temp gauge sensor is in the drivers side head

Running down the highway at a constant 2500 RPM and 80 MPH for about 10 minutes. Very light part throttle. Dead consistent on the speed for a long time. I looked down and noticed that the temp was at 230. It usually runs around 180 degrees on the highway. I kept my foot in it (part throttle) for another minute or two and stayed at 80 MPH... the temp creeped up to 240. Then I dropped it into neutral and coasted in idle. After about 15 seconds the temp dropped from 240 to 180 over a period of about 5 seconds. It just dropped pretty much immediately. Then the car ran like normal the rest of the drive home.

What might have caused that?

Thanks!

Is this the first time this has happened with the combination you described?