Several have explained why the cheap gauges indicate zero when they get hot. A carb running out of fuel (although that's not your problem) does NOT cause an 'drastic increase in water temperature', the engine would stumble, miss, then quit.

Overheating on C3 Corvettes is the #1 most common complaint. Do a quick search, you'll find hundreds if not thousands of posts.

There's lots of people here that would be willing to help, maybe listening to their experience without an attitude would prompt them to post.

 

Does the car only overheat when you drive or will it eventually happen if you just leave it idling?

If it gets hot while driving does it cool down if you stop driving and just idle?

What is your ignition advance at when cold at idle and at 2500? What is it when the car is at the overheating point for both idle and 2500?

My post about the gauges was a warning of those stupid glycern filled gauges giving bad reading when hot.

Does your fuel tank have a vent? Is it working? When hot pull the gas cap make sure you arent building up a vacuum in the tank?

Maybe you are on the right track that the fuel pump is giving you issues after its been running a while. I had a fuel injected car that would stall out while driving highway speeds for more than about 5-10 mins. Never happened around town and I had to let the car sit for about 10-15 mins and it would start again. Turned out to be a bad intank fuel pump. Again it was only occurring when driving at highway speeds.

Your pump may pump well with a hose disconnected but it may not be able to build pressure after a while when it up against a head like a regulator or the needle and seat.

Friend of mine had an overheating problem on his 65 convertible. He had someone rebuild the carb and they did something to the jets or a circuit in the carb and he wound up with all kinds of overheating issues until the carb guy figured out it was his fault. Car never overheated prior to the carb rebuild. Fixed the carb issue and the car ran fine. So lean conditions can certainly overheat you.

I looked your pump up on summit and they recommend only one filter and that is before the pump. You say you have one before and one after. You might be giving the pump a heart attack.

A top quality
fuel filter at 70 micron or less


The instructions say you must use a regulator and that's why they include one? You say you aren't using it?
The 12-150
HPfuel pump requires the use of a fuel pressure regulator.

What gauge wire are you using to the pump? USE A MINIMUM OF 14 GAUGE WIRE

 

I mounted the pump perfectly vertical on the rear frame on the passenger side and is approx. 8-10" from the exhaust pipe. It is mounted lower than the gas tank and the gas line that runs from the gas tank exit to the Pump is ran on a downward slant to the inlet of the pump . The supply line coming out of the pump takes long radius turns where possible . There is no kinking taking place during the operation of the fuel pump .. not even when the fuel guage registers 0-2 psi .

I think what im going to try is : Once the fuel guage registers 0-2 psi , Ill shut off the engine and take off the fuel line near the carb and see how much fuel if any, it is pumping out.

Again, the system worked flawlessly for 6,000 miles up until now.

 

YouGotDave,

***LONG POST****
Please bear with me because I have given some SERIOUS thought about your problem and trying to put the "pieces" together and I have concluded that there are some issues I would like to pass along to you. I am in belief that your pump is bad. And here is why. Also understand I work on Corvettes with in-tank fuel pumps often. So some of my thoughts on your issue transfers to the fuel systems of these types of Corvettes and what is different in your system...versus those factory Corvettes with high pressure fuel systems.

I am wondering how hot your fuel pump gets just running on its own and not with the engine and exhaust heat adding to it. Take the line off of your fuel pump AFTER it and connect a hose and a pressure gauge ( if you can) and PLEASE BE CAREFUL so you can check the head pressure of the pump while it is running. You may also install a small valve that could allow you to allow some gas to be able to exit the system ( much like if the car was running and using it) from time to time. Run it for the time that your problem begins to occur as you have mentioned. And if it does begin to drop pressure. Check and see how hot the fuel pump is. Even check it by touching it carefully. If you have an Infrared thermometer...check its temp and record it. Also check the temp of the wiring going to it also. And if you do not have one installed...I would HIGHLY recommend installing a good relay to power it up instead of direct wiring with a cut-off switch....and if it is not already...install a fuse in-line to protect the circuit. The reason for checking your wiring (which I think you stated you had checked) for getting hot is that if the pump is wearing out...it can begin to draw more current and allow the wiring to get hot if the resistance inside the pump is great enough. Also if you do not have it fused...do so and see if the pump blows the fuse when it begins to fail. I think you wrote it draws less than 5 amps...so I would install a 5 amp fuse in-line.

There is a tool I use at my shop that allows me to measure the amount of amps a component is drawing when operating. It is a very helpful tool...not saying you need one...but it would help to see if the pump is drawing more amps than it states it is requiring to operate. Sorry, I do not at this time have the name of manufacture and part number to aid you today. I am not at work. But the tool has a lobster claw type clamp that goes around a wire and can read the current in DC amps.

The reason I mentioned the above test is that factory pumps are in the tank. The fuel keeps them cool ALONG WITH the system has a functional fuel return in place. SO when the factory pump is running ..it is NEVER allowed to pump fuel and the fuel NOT flow...due to the fuel return. SO...your fuel pump is running and the fuel in it is stagnate...and NOT FLOWING...or if it is ..very little due to your have to figure...how much fuel can be in your hose AFTER the fuel pump. Lets say 1 quart. And figuring on your MPG...how long or far do you have to drive to use the fuel that is in your fuel hose after the pump. You have to figure in idling and cruising speeds...versus wide open throttle. And then...the fuel that is now in a "possibly" heated fuel pump...is trying to pump fuel and is beginning to fail due to the lack of FUEL RETURN....and the pump is pumping like crazy and the fuel is going ...basically no where at any considerable rate. REMEMBER...ALL electric fuel pumps that I have ever worked on had a fuel return...and if I installed an electric fuel pump on car...that was not factory...I made sure it had fuel return...even if I had to fabricate a fitting to allow fuel return. This prolongs the life of the fuel pump. I do not know the design of the pump you are using...in regards to the internal structure and where failure can occur...such as seals, vanes or diaphragm. BUT if I were a betting guy... I would bet it is your pump.

Also...most electric fuel pumps head pressure is greater than what is required to operate the car...as the fuel pressure regulator sets the pressure for proper fuel pressure operation. So having a fuel pump that is right at where you need the pressure to be for to function...is fine...but if you think about the pump working like crazy to pump fuel and can not due to the fuel being pumped is not being used at a high rate all the time...thus...just pumping the same fuel...again and again...chances are the internals of the pump can begin to fail. Possibly using a higher fuel pressured pump along with a fuel pressure regulator and fuel return might help you not deal with this issue again. Being on the "edge" of maximum pressure and having a problem...is a "problem".

Also...many of the electric fuel pumps are intended for off-road use. High RPM, fuel usage and sometimes not running for hours constantly. I know fuel pumps have come a long way...but 1/4 mile "blasts" are not the same as "stop-and-go traffic".

I do not know it this helped....But I hope you get this issue corrected.

DUB

 

Yes, it made good sense and ive considered the fact that the fuel may be just 'pooling' at the Fuel Pump not being a Return Type Pump since its preset at 7 psi . A long time ago, i did have a Holley 'Blue' Electric Fuel Pump , 15 psi , with adjustable Fuel Regulator in the engine bay .. and it worked flawlessly. I got rid of it because it was too noisy for my liking and went with the Holley Gearotor Pump that i have in it now. The pump i have now is rated for 750 h.p. which is huge overkill for the 540 gross h.p. im running now. So , i think you have most likely accurately described whats going on with it.

Before, I opt for another Fuel Pump, im going to take a few IFR Temp. readings and see how hot its getting . Could be a good portion of the fuel is vaporizing before it even reaches the engine bay (?)

Ill get to that this weekend then post the temps. Thanks much.

 

Getting another pump with fuel return provision in it. I do not think I would go that route due to the fuel return is right at the pump....AND...the fuel in the line after it is still just basically sitting there and not moving at light cruising and idling. There is another way of creating a fuel return with what you have now and use the factory fuel return line (if it is still on the car). I do not know if the current pump in the car will work due to the pressure is right at the limit needed. The pressure may drop once a fuel return fitting is added.

"Gearotor"...seems like it would have vanes in it that can fail when hot or possibly trying to move fuel that can not go anywhere due to the lack of a fuel return in place.

Hopefully your temp readings help fill in some missing information that can allow a final decision can be made to correct this problem.

DUB

 

Those fuel gauges are useless and have nothing to do with you overheating I found this out over 10 years ago, I thought they would have fixed it by now.

How fast do you think you can go with 0-psi fuel pressure or do you think it would stumble and stall, throw the gauge in the garbage.

 

The attitude i have, is when a Poster makes a definitive assertion regarding diagnosis in half a sentence or less. If youre going to contribute in trying to help someons predicament as a Fellow Corvette Owner, then please add a few more sentences of elaboration.

 

Thanks for your tips and info. You are mistaken on my pump...its not the 12-150 but its the 12-125 thusly : http://www.summitracing.com/parts/hly-12-125 . This pump is preset for approx. 7 psi and doesnt require a Fuel Regulator .

Once the engine overheats, it stays like that regardless of highway speed or idling. And it doesnt begin to overheat so long as the fuel guage is at 4 psi or higher ive noticed. It takes approx. 20 minutes of running the engine at any speed , till the guage drops from 7 psi starting out ....to 3 or 4 psi. Then it slowly decreases from there. The carb float levels though, show a steady level of fuel at the half-way line thru the windows which is odd.

Yes, there is a disconnected fuel return line right at the gas tank since the Fuel Pump im using is preset at 7 psi and doesnt require a return.

Im going to take the car for another spin right now and will take off the vented gas cap after the first 20 min. of driving to see what happens ; ill also take IFR Temp. readings on the Fuel Pump at various times thruout the 20-30 min. drive. , and will list them here soon.

Thanks to all who have contributed. I cant tell you how annoying this thing is...so much so, that ive considered selling the car disclosing its current problem. But ill try to muster up some more patience first.

 

Sorry about the ref to the wrong pump via the link?? I clicked the one you posted and it dropped me on that pump at summit but I didnt notice the same directions were for 2 different pumps with a chart showing the differences....

Dont get discouraged... think how good you'll feel when you fix it.

I did a quick search on the web for your pump and I found several posts on chevelle and camaro forums indicating an issue where after a couple of years the pumps started to get hot and then slowly fail to pump properly after heating up.

Seems gerotor type pumps are more prone to issues than the vane style.

What filters are you using do you have the numbers? Wonder if they are restictive in flow epescially since you have one before and aft.

 

Wait, if your float bowls are full to the site hole, you have enough fuel in the carb to keep it running. Are you sure you have spark when it dies?

 

Hey. No prob. on the Fuel Pump mistake. Heres the two fuel filters i have before and aft : http://www.summitracing.com/parts/sum-g1508/overview/ . I may take the aft one out just for kicks and see if it makes any difference. It hasnt up to this point.

Heres the scoop from my run with the car just now :

1. Overheating problem solved ; had a very small coolant leak at the thermostat housing and since its almost all water in the system...i didnt see it . Must have evaporated each time. Filled up the expansion tank and no more overheating problems .

2. a. At startup of engine and left running : Pump temp was 84 f. / Pump vdc 13.6 / Inline Summit liquid-filled Fuel Guage temp (engine bay) 85 f. / Guage pressure 6.5 psi .

b. 15 minutes later after some city driving and with engine still running : Pump temp 100 f. / Pump vdc 13.6 / Fuel Guage Temp 133 f. / Guage pressure 2 psi .

c. Another 15 minutes after some spirited highway driving with engine still running : Pump temp 115 f. / Pump vdc 13.6 / Fuel Guage temp 144 f / Guage pressure 0 psi.

At this point, definite fuel starvation indication is felt in the operation of the engine ; its hesitant unless i go kind of heavy on the gas pedal and then it runs smooth. WOT is perfect with no hesitation. Also , at cruise speed of 45 mph , occasional minor backfire while starvation is felt. Notes : Brand new plugs (.035") ,plug wires, brand new cap and rotor -- I dont think its an electrical miss im feeling...rather, fuel starvation . I rechecked the wires for shorting and to make sure they are routed properly to each plug. The firing order is correct at the Distributor Cap. During the run, i took note of the carbs fuel bowl level...and neither bowl moved from the half-way level .

So...Im also thinking it is the Fuel Pump at low level operation and its fine at higher level operation such as heavy acceleration. Your thoughts ? As for the fuel guage, I dont know if its reading true or not. It could be . Its the second one ive tried , and, brand new. If its fuel starvation, how come the carb bowl levels are fine ? Can you get fuel volume without much pressure behind it if the Fuel Pump is faulty ?

Also, who makes a decent inline fuel guage for the engine bay ? Should i try relocating the guage to the outlet of the Fuel Pump to get it away from the engine heat , and see what i get ? Should i remove the aft Fuel Filter to see what happens ? I guess after doing these things , replacement of the pump is next (?) Should i go with a Holley 'red' electric fuel pump (preset at 7 psi) next time even though its noisier than the Gearotor Pump i have ?

Thanks much for the time youre putting in here with me. Dave.

 

The engine doesnt die. After some 30-40 minutes of engine operation ... it feels as though its not getting enough gas even though the carb bowl levels are remaining at the halfway line. And if i go heavy on the gas pedal, it runs great . Im still of the opinion that its related to the Fuel Pump but not 100% sure at this point.

What im going to do which i havent done thus far, is, take the car for a good run at night and check the plugs and plug wires for a potential lazer-light show as I had a set of Summit wires once that were arching on each other. But again, it feels like fuel starvation to me when it happens.

 

When it starts to stumble, shut it down, coast to a stop, check the site plugs. If you leave the ignition and pump on, it could refill the bowl while you're slowing under light load.
Running good at wide open actually sounds like a rich condition, It also could be ignition secondary. I've seen coils fail as they warm up.

 

Ok., i shall try what you said here. Wont be till Sunday now that ill have a chance to spend more time with the Ol Girl.

 

After reading the posts after my last one....and your responses to tests. I feel it is not in your fuel pump now. BECAUSE...if the fuel level is not dropping....and you can "get-on-it" and it will run out GREAT and does not cut-off or feel that it has run out of fuel....then it is not your fuel pump ( in my opinion) because it does not matter what your PSI reading is...it deals with volume of fuel delivery or GPH. The main reason as you probably know why you are using a pump rated at 7 psi is so you do not force fuel past the needle and seat. If the pump is feeding the carb with fuel and the fuel level is not dropping...your issue is ignition/timing related...or possibly still needing a fuel return to keep the fuel moving and "cooler" so to speak. Because...as you know...the carb does not require fuel pressure to make the accelerator pump work when you go and accelerate.

You REALLY do not know if you are losing fuel pressure...because you are trusting a gauge that goes in-line...versus...adding a hose after the pump with an appropriate fuel pressure gauge made for checking fuel pressure and test it again and see what happens when you just run the pump by itself without the engine running. Also...I have to kinda agree that you may be running a bit rich...but I would get the fuel return corrected if it were me. But I would investigate the ignition thoroughly. KV test the wires while running and check timing as long as you know for a fact that the notch on the harmonic balancer is correct and has not moved. This is so if you time your engine with a timing light...you are not setting the timing to a bad balancer that is "off-time" on the notch.

DUB

 

But if it were ignition, then why doesnt it start running rough right from the get-go ? Why would the ignition cause roughness ONLY after some 30-40 minutes later ??? Doesnt make as much sense to me as the Fuel System being the culprit ...but at this point of frustration...ill try anything .

Heres my game plan for today :
a. Run the car till it starts to stumble , then do as the other Poster said which is to immediately shut off the car (and fuel pump) and coast to a stop ...then observe the carb sight glasses.

b. Wait till the engine stumbles, leave the car running at idle, then quickly remove the gas tank cap to see if i hear a whoosh. Then with the cap off, observe the fuel pressure and see if it returns to normal.

c. Wait till nighttime, then watch for shorting/grounding of the ignition wires and plugs while at idle and fast idle.

These will be the last efforts i can make on the car, today, for a couple weeks as im going out of town. But ill post my findings here later on today.

MANY many thanks for all who are staying with me on this thread and are truly trying to help me out. Very good ideas and useful info .

 

Many ignition problems- HEI or conventional coil- surface once the engine gets really hot.

 

I have seen the modules in a HEI "act-up" when ti got hot due to the lack of sufficient dielectric grease applied to the mating surface as designed.

Also I have encountered a pick-up coil that would loose contact in the two wires when the engine would rev up off of idle.

We will wait for your return and see what happens in the tests you apply.

DUB

 

Yesterday i took it for another short run., before leaving for out of town : Oddly enough, it started to stumble/miss right after i started it ....which hasnt happened before. It stayed like that even after it was fully warmed. After 20 minutes i shut off the car and fuel pump and coasted to the side of the road to check the carb fuel bowl levels...and they were still at half way. (the fuel guage was at 0 psi). I had a look at the Summit page for the fuel guage i bought from them, and to my amazement it says that when the temperature of the guage increases, it will cause the reading to drop ! So, i guess that eliminates the fuel system from being the culprit and instead...it is ignition related. Also, i popped the gas tank cap open with the engine running and there was no whoosh. So, when i get back in town, ill start attacking the ignition system starting with observing the engine when its pitch dark outside ; I think im going to find some shorting and/or grounding going on. I can hear a fairly loud 'tick' occuring every now and then from the area of the Distributor Cap so ill pay attention to the cap when i check the engine in the dark. Sadly, that wont be for another 2-3 weeks so keep subscribed to this thread for when i return .

Thanks for everyones help thus far. Dave.