I have a 1978 F-150 4WD with a C-6, 400 motor. The motor tends to overheat on long drives or on hot days(85Deg+). The motor is completely stock, and the original motor( I am the second owner). I have only had the truck two years, so I don't know any problem history.

Here is some background:

New everything on the cooling system to include fan, fan clutch(severe duty),
water pump(motorcraft), radiator(extra cooling with 2 3/4" deep tank on top),
radiator hoses and heater hoses(lower hose has the spring). Engine block was flushed with a prestone solution, prior to installing the new radiator.

The shroud is original, but in good shape. I also have the rubber flaps installed on the top of the radiator. It has AC. The cooler for the AC has no obstructions.

Installed a new 180 degree motorcraft thermostat and verified that it does open at 180 Deg.

I have good flow through the radiator when the thermostat opens up.

I have installed a temperature gauge with a sender, and the gauge reads 180 deg when the thermostat opens up, also verified with an infrared sensor.

There is about a 20 degree difference in temperature between the top and bottom of the radiator.

The new temperature gauge reads about 230 deg F and can climb up to about 240 deg F when climbing hills. At one time the temperature would climb when going up a hill and then return back to 220 deg F when going down the other side.

The engine timing is at 8 BTDC at hot idle, and I can watch the timing advance when I increase engine speed, so I think the vacuum advance is working. There is no engine ping under load either.

There don't seem to be any issues with the transmission. It shifts smoothly with no loss of fluid and the fluid is a nice bright red color still.

The one thing I have noticed, though, is that I get a lot of bubbles in the system. However, I am not getting any water in the oil, nor am I seeing any white smoke in the exhaust. The pressure of the cooling system doesn't exceed 13 psi(doesn't overflow) and I am seeing no level change in the radiator(high or low).

I am wondering if the back cylinders are getting hot enough to start the boiling process, which would cause the bubbles. I have burped the cooling system many times, and can't get the bubbles to stop.

Sorry for the long thread, and rehashing a common topic, but I have researched a lot of threads and can't come up with a reasonable solution to the problem. Carbon buildup? Head gaskets? ???????

 

180°F thermostat? It should be about 195°F and of the proper design for a 335 series engine. They are not standard thermostats. They have a type of skirt on them to control the bypass flow. If the skirt is not present the rear cylinders will get too hot.

The timing will increase with engine speed if the mechanical advance is working. This is not an indicator that the vacuum advance is working. Pull the vacuum line and verify that the mechanical advance is working by speeding up the engine. Then hook the vacuum line to manifold vacuum to verify that the vacuum advance is working.

Verify that your temperature gauge is calibrated correctly. Drop the sensor into some boiling water (heated with a torch). Make sure you correct for elevation. Water boils at 212°F at sea level. You can probably find elevation corrections with Google. A thermometer in the upper radiator tank will read 5-10°F cooler than the engine outlet temperature.

How did you measure the cooling system pressure?

 

Long threads tend to generate fewer question. One of the problems with this series of motors is the internal bypass system Ford incorporated into the block. The engine arrives at normal operation temperature by NOT passing water past the back pair of cylinders until the thermostat opens and closes the bypass opening. Looks real smart on paper. However in the real working world it has some problems. The first problem is the thermostat. If the incorrect type is used it will not close off the bypass when open and therefore will now force coolant past the rear pair of cylinders. You will appear to have great flow to the radiator when the thermostat opens but the rear cylinders are not being properly cooled. This leads to overheating problems of course but also will eventually cause to rear cylinders to loose their ability to seal properly from extensive overheating. Don't skimp on the thermostat. Buy the best you can get and make sure it has the sealing ring on the end which points down. It should also be 195 degrees. Your fuel burns more efficiently at higher temperatures. The other main problem of this design is the fact that by not always flowing coolant pass the rear pair or cylinders, deposits tend to accumulate at the bottom of the water jackets in those areas. I found the out when the freeze plug behind my starter rusted through from the inside. Upon removing the starter and prying out the bad plug I found a lot of rust deposits in that back corner of the block. Bad enough in fact that I removed the plug on the other side only to find the same problem. I never really got rid of the problem until I installed a remanufactured long block a few years later.

 

Thanks for the replies. I purchased a thermostat from the ford dealer for that particular engine and year. Do they not supply the right thermostat? I did not measure the pressure of the cooling system, but assumed that the system is less than 13 psi, since the radiator cap is not relieving any pressure. I can't find a parts house that carries cooper-robertshaw thermostats( No Advance Auto in this part of the woods). The temp gauge does indicate correctly, as verified by a thermometer and corrected for altitude at 3500 feet.

 

it's possible that even the Ford dealer screwed up. the correct thermostat does not look like other normal Tstats, it should have an extension on the bottom of it that others don't have. i've actually never had the "right" Tstat in any of my Clevelands and have never had a temp problem either?

 

I don't think Advance has them, try Auto Zone.

Have you checked your timing and mixture?

 

I realize it was a long thread, but I did state that the timing was @ 8deg BTDC. The antifreeze mixture is 50%(new fluid after the new radiator was installed. I did e-mail the people on the standard-cooper website to ask them for a distributor for Montana. Thanks for the help.

 

Yes I read your long post...

Have you checked your timing properly according to the book with the proper procedure? Have you checked the mechanical and vacuum advance like I asked?

Have you eliminated harmonic balancer shift that causes the timing marks to be off?

Have you checked your carb mixture with a meter?

Have you checked for timing chain wear? If the engine has more than 80,000 original miles it is time for a chain check and replacement. Check b4 replacement to make sure it has not been replaced already.

How is your oil pressure? Low oil pressure can cause the lifters to not operate correctly which can lead to overheating. It can also quickly lead to engine failure. Or it might limp along for years...

 

(I meant to post this in this thread earlier, but got distracted and accidentally posted it elsewhere...)

There was another thread on a similar problem and thermostats earlier in the year.

http://www.flowkooler.com/thermos.php

Look at that page and scroll down to the 333 model. Did your thermostat look like that? Notice the lip that seals off the bypass in the block.

I was really pleased with how my truck's cooling system performed this Summer. I'm using a 2-core vertical flow radiator out of a Slopar motorhome, a 2200 CFM electric fan, and a Robert Shaw 333-192 thermostat. Cheapo remanned water pump from Napa, and a 50/50 mix of h20 and Prestone. I've never seen that motor get over 205, whether it's idling in a traffic jam or doing 70 up a grade.

 

Go_Racing84, I do not have the proper thermostat, according to the drawings on the flowcooler website. Thank You.

Torque1st, Thanks for the info. I will take a look at the service manual to make sure I am checking timing correctly. I don't know about the condition of the harmonic balancer. Low oil pressure may be an issue, if the gauge is reading correctly(stock gauge). It does read on the low side when the engine heats up.

The engine has about 100,000 miles and is original. The timing chain may need to be looked at.

Please bear with me, I am an amateur still in the learning stages.

 

The OEM chain had nylon teeth to reduce noise. It fails repeatedly at about 100K miles. One of those planned obsolescence things...

Replace it with an aftermarket unit that has multiple timing positions. Use the straight-up or 0° setting. Do not get the OEM replacement set or it will be retarded 4°.

The harmonic balancer ring frequently fails due to age and oil which shifts the timing marks. If it fails completely and comes off it can do a LOT of damage under the hood and ruin all of those nice new parts you put in.

 

ever since I built my 400 it has heated up when driving on the roads when it is hot out side. never past 210 per my guages, but it is too hot in my mind. I have been running a robertshaw tstat since the build, but honestly I have no idea which one I have in there from them.

I will have to check them out since I am putting on a set of closed chamber heads and EFI to the mix.

 

As a side note, I had a Mr Gasket high flow thermostat in mine, replaced it with a Robert Shaw based on the info here. It is the same thermostat, just repackaged.

 

Thank You eveybody for all the information. I am searching for a replacement thermostat.( Choices are limited in this area.)

 

i wonder if you have a bit of built-up scale that has come loose and is blocking the passages at the head gasket? wouldn't be the first time, and it's hard to figure out until you tear it apart. only 20* difference through the radiator doesn't sound like a lot/enough?