high exhaust header temps on 230 engine

[wiboater]

I have a 36 dodge LC pickup with a 1942 power wagon block that I had rebuilt, bored out, new pistons and valves etc. It starts and runs great and has plenty of power but I now have a problem with the carbureator bowl getting so hot that the fuel in it boils. When I checked temps with a heat temp gun it said around 500 degrees on the exhaust manifold and I think it was about 140 at the carb bowl. This happens in summer in hot temps. I have put an electric fuel pump on to solve it but seems like it shouldn't be getting that hot. No problem with the radiator overheating and I checked timing and valve clearance etc. those are ok. no exhaust restrictons. Any Idea's or is that a normal temp now that it's bored out? I've had the truck since the early 70's and had a 1949 dodge 230  in it before and never had vaporlock problems with it before the engine overhaul with the powerwagon block. 

[Robert Harrison]

I googled exhaust temps and it said 400 to 1600 degrees.  So I don't think that is it.  Could it be something with the heat riser?  If you undid the exhaust pipe you could look up there and see if it is closing or not closing tightly I would think?  Your cylinder head temps should be about what your thermostat was set to.  There should be a thick spacer under the carb this prevents heat transfer.  Did you check with your heat gun what the temp was at the fuel bowl?  Over bore should not make a difference.  There are no significant differences in the blocks you are talking about.  I dont think this is it but what was done with the cooling distribution tube that is inserted into the block from the water pump opening?  Was it replaced, cleaned or reinstalled?  Bob Harrison

[JBNeal]

Maybe take that infrared thermometer and look at your entire cooling system.  If'n ya got high exhaust manifold temps and a radiator that is not much above ambient, that water pump might not be moving coolant sufficiently because of an internal problem such as a floating impeller or an external restriction such as a thermostat that is not opening properly.  A clogged or leaky WDT will also cause more heat to soak into the rear of the engine rather than circulate through the cooling system.  If the radiator has hot spots + cold spots, there might be some blockage there.

 

FWIW I have an exhaust temp gauge in the QuadCab, and the 5.9L Cummins normally gets up to 400°F at idle in above freezing ambient temperatures.  This straight 6 diesel is about twice the size of the pickup flatheads, and pulling a load of 5000# up a grade, the exhaust temps get up to about 1000°F with about 15psi boost, but within a minute of getting back to flat road, temps drop back to 700°F at about 7psi boost.  And after driving like this all day, idle temps get back to 400°F within a minute or so...it's been running like this for 250k, no mods beyond 4" exhaust upgrade and 15psi fuel pump.  Coolant gauge temps get up to 200°F in above freezing ambient temperatures and pretty much stay there, even in TX summer heat.

 

So 500°F sounds a tad high for the lower output flatheads, even in the summer.  The only time that I have seen temperatures that high on a gasoline engine was when I was working on a GMC being converted to run on propane...that involved trying to deal with some GM emissions blackboxes kept leaning out the carb after the truck went to closed loop operation.  I didn't need a thermometer to know that something was wrong with the truck as opening the hood felt like opening the oven on a Red Baron that was ready to serve 🍕

[wiboater]

On 12/15/2024 at 11:33 AM, Robert Harrison said:

I googled exhaust temps and it said 400 to 1600 degrees.  So I don't think that is it.  Could it be something with the heat riser?  If you undid the exhaust pipe you could look up there and see if it is closing or not closing tightly I would think?  Your cylinder head temps should be about what your thermostat was set to.  There should be a thick spacer under the carb this prevents heat transfer.  Did you check with your heat gun what the temp was at the fuel bowl?  Over bore should not make a difference.  There are no significant differences in the blocks you are talking about.  I dont think this is it but what was done with the cooling distribution tube that is inserted into the block from the water pump opening?  Was it replaced, cleaned or reinstalled?  Bob Harrison

 

[wiboater]

I actually took off the exhaust manifold and fixed the heat riser It was stuck in the non heating position so it wasn't the problem. Even with the 160 thermostat in the truck the heat gauge gets up to around 200. but stops there. Temp when I put the Infrared heat gun at the thermostat housing is Ok . It's the exhaust manifold that seems to me to be getting too hot. I don't have any problem with the 230 I took out and put into a 38 Dodge Pickup I don't have vapor locking and that manifold runs cooler.  I put the engine on the 36  together when I had it rebuilt and I am pretty sure I checked the water distribution tube at that time. I also think I put a new water pump on it then but can't say for sure ( old and forgetful now). I did get the high reading at the carb bowl  and I took the carb apart once and watched the bubbles in the fuel bowl when I removed the top of the carb. Are you talking about the aluminum spacer they had? I think it's on there but I will have to look. I want to put a Phenolic spacer on about 1/2 inch thick or more and try that but have to find one first that doesn't cost a fortune. I don't think that the muffler is restricting flow because I have plenty of power and the truck starts and runs great . Just doesn't like hot weather. Anyway i  was hoping maybe someone else had the same problem and solved theirs. I won't be able to try anything now because of cold weather here. I appreciate the ideas though. I am a little suspicious of the water pump but the temps seem consistent on the engine block. 

Edited Monday at 09:52 PM by wiboater

[Los_Control]

I think it is the modern fuel .... the recipe has changed over the years, modern fuels boil at a lower temperature  causing vapor lock.

 

This would explain why you have the issue in 2024, but not 10 years ago.

With today's fuel systems, electric fuel pumps and a return line ... modern cars are not affected by the changes.

 

For many, adding a electric pump is enough to take care of the problem when it arises. .... Basically install the electric pump and call it a day.

 

I wonder and have a plan to install a return line .... Some on youtube have installed a return line, and claim the fuel circulating through the lines never sit long enough to heat up and cause vapor lock.

I like this idea because it is preventing the problem from happening in the first place.

While the electric pump is a fix for after the problem occurs  ..... choices.