Coolant Temp Issues

[Fleetwood Meadow]

My ‘52 Cadillac is fighting me again. The temperature gauge is only showing 1/4 of the way up the gauge and the carburetor is vapor locking on me. I checked the inner and outer radiator hoses and they were 209 and 185. So to me that indicates that the radiator is doing it’s job. Clearly the gauge is not measuring properly. Not sure if the gauge can be 12 or 6 volt dependent but the sending unit is 6 volt as is the rest of the car. However I don’t know what the owner before me did in terms of the gauges. What is my next course of action in terms of checking and correcting this. I have to keep turning on the electric pump in order to keep the carburetor full. 

[hchris]

Sounds like you might be dealing with two issues at once.

 

As to the temp guage, do you know if its an electric sender unit or bourdon tube sender ? electrical will have a wire coming off of the sender unit, bourdon tube will be a sealed unit with thin copper tube from a fitting in the block back to the guage.

 

Electric units work with a change in resistance as the temp sender unit heats up, fairly easy to fault find if you have a multi meter and know the resistance value of the sender.

 

Bourdon tube is another matter, essentially the copper tube between sender and guage is filled with ether or similar and sealed up, the temp changes the volume of enclosed fluid and raises pressure within the sealed tube, at the guage end this pressure moves the needle mechanism; same principle as an oil pressure guage. More often than not the tube is fractured, soldered fittings crack etc. and the fluid leaks out thus the pressure element is lost and guage ceases to function or, with partial loss, under reads.

 

With the vapor lock issue there are hundreds of previous posts on the problem, do a search through the forum for various remedies. 

[Fleetwood Meadow]

It is an electric sending unit. I have never had good luck searching for anything on this site. The other question that I am struggling with is why is it so hot? That will cause my vapor lock issue. It’s a new water pump that is working, a new thermostat that opens properly, the radiator is working, and I have flushed the engine block. 

[edinmass]

If your problem really is vapor lock, the best solution is to run a return line from the carb back to the tank. You can run an electric fuel pump at the factory pressure, and you will never have a problem again. You must be careful to install the line in a safe way in the event of an accident. The return line needs to be smaller than the main line. The fuel will circulate and eliminate the problem. We can only buy E10 in many states, and if you want to really drive the car, you need to make it run right on the modern fuels available. 

[Fleetwood Meadow]

Ed, I’ve been toying with the idea of a return line. As 48 said, ethanol free gas is probably the way to go and there is a place in town that sells it in the form of racing fuel but I struggle with paying an extra dollar a gallon in a car that has a 20-something gallon tank and 11 mpg. I’m sure the return line is simple in design but where and how does it connect to the existing fuel line and gas tank?

[ted sweet]

simplier to pay the extra dollar a gallon

[Matt Harwood]

55 minutes ago, 48Firetruck said:

This is the pump I used on my 42 Cadillac, it comes in 6 or 12 volt from Summit Racing. It's an on demand pump, 4 PSI, and has flow through capability. I mounted it in the original fuel line on the frame just ahead of the gas tank and have a toggle switch hidden under the dash board. I leave it off for normal driving and operate with the original mechanical fuel pump. When the car starts to get hot and stutters due to vapor lock I flip the switch and the problem goes away almost immediately. It's also nice to use as a priming pump when the car has sat for a while so you don't have to wear your starter out trying to get fuel. There's no need for a return line back to the tank as long as you float valve in the carb is in good shape. When the system hits 4 PSI the pump will just bypass itself.

 

Pump is an Airtex E8902 (6 volt) and E8251 is the 12 volt version.

 

 

Try this first. Quick, cheap, easy, and likely to solve the problem (and as a side-benefit, it will make the car easier to start after a period of sitting). Better than chasing special gas and easier than a return line. All my cars have electric pumps on them to assist the mechanical one. My cars start instantly and don't have problems in the heat, no matter how hot it gets.

[Fleetwood Meadow]

I have an electric pump. But that’s not the problem that I’m trying to tackle here. My issue is the 209 degree coolant temp when the thermostat is 180. That seems way to hot and is vaporizing the fuel. I should not have to operate an electric pump when the car didn’t come with it. They were able to keep the car running with its mechanical pump. I understand that when outside temperatures get high or the car is sitting too long idling there is a rise in temperature and the electric pump will temporarily fix the issue but I need to get the engine temperature down to the appropriate temp first and foremost. 

[Matt Harwood]

Thermostats only regulate the minimum temperature of the coolant, not the maximum. If your radiator can't reject enough heat to keep the coolant at 180 degrees then the thermostat is simply wide open all the time. Changing to a cooler thermostat only changes when the thermostat opens (earlier) but may not have any effect on actual operating temperatures if the radiator can't reject enough heat to chill the coolant down to that level. I still suspect clogged coolant passages in the block or a blockage in the radiator, but if the engine isn't tuned correctly you're going to be putting extra heat into it as well.

 

As far as the electric fuel pump, what 48Firetruck says is 100% correct. Today's fuels vaporize at much lower temperatures than fuels of the '50s. That's why they had to put exhaust crossover tubes in the intakes to keep the carburetors hot: to help the old fuel atomize better. Today we have the opposite problem and fuel vaporizes at not much more than room temperature and will boil well below 200 degrees (go ahead and put a few drops on your driveway and watch how fast it evaporates). That's why electric fuel pumps are helpful--as the fuel is hitting hot spots in the fuel system and boiling, usually inside the mechanical fuel pump or line to the carburetor, it continues to push liquid fuel through. A mechanical pump can't move vapor, and if the fuel is vaporizing inside the pump, fuel flow stops and the car starts to stutter and misfire. Electric pumps keep the fuel moving when the mechanical pump is moving close to 0. In addition, the electric pumps put a little pressure in the lines, which can help stave off boiling in some situations. Proper use of an electric fuel pump can really reduce heat-related fuel issues.

 

If you have an electric pump and the engine starts to stutter, turn it on. It's not because something is wrong, it's because today's gas is different and old cars weren't designed to cope with it. It isn't a crutch or a band-aid fix, it's an upgrade that helps solve a modern problem many old cars face.

 

You should also understand that getting the engine's operating temperature down will not significantly alter under-hood temperatures or change your fuel issues. Even if it's running at 180 degrees, it's still making heat that has to be rejected by the radiator, which is in the engine compartment. The exhaust manifolds are still 800 degrees or more. Coolant temperature is only a reflection of coolant temperature. It doesn't necessarily mean the other parts of the engine are any cooler. A 20-degree shift in coolant temperature won't make much difference in the ambient temperatures underhood.

Edited July 25, 2019 by Matt Harwood (see edit history)

[RussJagoau]

As an owner of a 51 in a hot climate, I also suffer with the vaporisation of the modern fuels in the summer monthes.

My 51 and 53 Chieftains have 170 degree thermostat's  installed and the radiator is in good condition with good heat transfer,   good temperature differential measured across inlet and outlet. 

As a suggestion you may wish to try wrapping your metal fuel lines in silver foil paper, as this acts a  heat shield and will prevent heat transfer from inside the engine bay. It will also determine if your issue is indeed fuel vaporisation or another problem with similar symptoms. It cured the cause on my old girl particulary after driving in warn days and then idling or parked for a while when the heat transfer takes place into the carburettor fuel bowl and fuel lines. I originally had it around the fuel bowl and it cured the problem, I have since removed it from the bowl and manufactured a more professional looking heat shield that is mounted to the original heat shield between  carb and intake manifold.

Suggest you try it and see what the outcome is, if it cures your vaporisation issue then that's a start.

Then you can investigate  the higher than normal temp profile across your radiator as it does seem quite warm  given the operating temps you stated.

 

[Fleetwood Meadow]

I have been using 15-40 in it. The book says 20 weight. Starting that car is a monster after it’s hot. It takes a lot of cranking and after a little bit of cranking I end up holding the gas pedal down to the floor and it finally starts up. When it’s idling I can see the bubbles in the fuel bowl. They put the pump on the upper crankcase breather so the lines going to it from the tank and going to the carburetor are on top of the engine. I have the one going to the fuel pump way above the engine, about 10” higher. When driving the car doesn’t act up but when idling after it’s warm it will shut off after a couple minutes of idling and I’ll have to turn on the fuel pump to get gas in it. When I had the pump running continually it caused problems because the 4psi electric pump coupled with the 4psi mechanical pump would cause gas to dump down its throat when the car was shut off. 

[Matt Harwood]

Heavy oil makes it harder to turn the engine while starting. If the manual says 20 weight, I might go with a 10W30 or a 10W40 to help when cranking. See what running oil pressure is when hot (weren't you having an oil pressure problem?). It's possible that the oil pump is struggling to move that thick oil.

 

Fuel pressure isn't cumulative. The electric pump pushing at 4 PSI doesn't become 8 PSI after going through the mechanical pump. The fact that you can see bubbles in the fuel bowl means the gas is boiling. That's when you turn on your electric pump. When you're driving, fuel is moving through the system and keeping things cool. At idle, fuel flow slows way down and the gas has time to collect more heat on its way to the carburetor. When it vaporizes or starts to boil, the mechanical pump can't move it anymore. After you shut it off, fuel flow stops entirely, coolant flow stops, and the engine just sits--this is called heat soak and is often why cars are hard to start when they're hot. Not only does it struggle to make spark (resistance goes up as heat goes up) but the gas that is already in the fuel pump, fuel line, and carburetor, is sitting there percolating. Again, turn on the electric pump and it'll push fuel in there and help the car start. Holding it at WOT can help so it doesn't flood, which seems to be what you're doing.

 

It's important to understand how all this stuff works and how it interacts and how the fuel behaves so you can work towards solving your problems. It's not just heat, it's not just the fuel, it's not just the fuel pump/line, it's a combination of all that stuff. Understanding the system is the first step to solving the problem.