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Spike in 340 temperature

  
Mopar Muscle
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Spike in 340 temperature

 
delse814 delse814
New User | Posts: 7 | Joined: 11/08
Posted: 05/07/13
07:21 AM

Has anyone ever heard of the temperature spiking then coming back down to normal? When cruising the temp stays about normal. When moderately accelerating the temp spikes on the gauge, then when back to cruising the temp comes back down to normal. At first I thought it was the thermostat so I changed it. Same thing. Next I thought it was the water pump, so I took the t-stat out and checked for circulation. Pump is circulating. It never ran hot prior to doing this. Radiator is new. It is a 1969 340 all original. Next step is to flush, clean and put in new coolant. Has anyone experienced this?  

Cudadon Cudadon
User | Posts: 202 | Joined: 02/08
Posted: 05/07/13
03:00 PM

Try jetting up some.  This might be a lean condition.

Don  

delse814 delse814
New User | Posts: 7 | Joined: 11/08
Posted: 05/08/13
04:40 AM

Thanks for your input Don. I thought of this as well but why would the jetting change all of a sudden? Maybe the gauge is going bad? Maybe a bad head gasket? Maybe time for a rebuild.

Todd  

waynep712222 waynep712222
User | Posts: 127 | Joined: 04/13
Posted: 05/08/13
06:42 AM

a few things...

with a cold engine.. you might want to perform a 15 second full flow fuel system volume test..

disconnect the ignition system so NO spark can be created..  verify...

disconnect the fuel line at the carb...  extend with some fuel hose into a clean clear 2 or 3 liter plastic bottle...   have a friend or use a remote starter button to crank the engine for a full 15 seconds... while you examine the pulses of fuel from the end of the hose...

you should have about 1/2 a quart of fuel in that 15 seconds..

restrictions in the fuel line... kinked tubing or hoses... clogged..  sediment in the fuel pump check valves... will reduce fuel flow.. and create random or inconsistent sizes of pulses of fuel ..

you will also want to either hold your finger over the end of the fuel line or use a gauge to hold pressure  see if it maintains pressure when you stop cranking...

some chryslers.. but i don't think your has a return line from the fuel filter or fuel pump to the tank.. i have run across several mopars that the return was allowing too much fuel return and the carb could not allow enough fuel in with the reduced pressure to keep up with increased speeds..

a long time ago.. on a 440 motor home.. it too would overheat on long upgrades.. my former boss changed everything.. water pumps.. thermostats. radiators..  fans...  turned out it was a restriction in the fuel line..  where the generator set was installed.. somebody used a multi sized tee.. you know the ones that say. not for fuel system use..  feeding the 440 thru a 1/16 hole..
the fuel pressure would drop on long grades... it did pass the 10 second fuel volume test.. that is a factory test... but it would not pass a 15 second... the fuel lines were 25 feet long..


dirt in the fuel bowls or sediment on the metering rods and main jets could cause issues..  

delse814 delse814
New User | Posts: 7 | Joined: 11/08
Posted: 05/08/13
08:47 AM

Thanks for the info. I don't think that the fuel flow is the problem though. The reason is the tank is new, sending unit is new, 3/8" fuel line is new and the fuel pump is new. They all have less than 200 miles since install. I also have a glass fuel filter and that shows fuel being clean. It doesn't act like it loses fuel. The temperature spikes when rpm goes over 2500. Under 2500 it is normal. I will give the 15 second test a try. Thanks again for the help.  

delse814 delse814
New User | Posts: 7 | Joined: 11/08
Posted: 05/12/13
05:41 AM

After some investigation I found the problem. A bad temperature sending unit. Thanks for the input.