Pulsation in the cooling system?

[junkyardjeff]

While working on my 55 trying to get the temp gauge working right and with a infared thermometer testing the motor while it warmed up I felt a pulsation in the cooling system,I could feel it in the hoses and would vibrate the car but would not overheat.  It would get up to a little over 200 at idle so I replaced the thermostat and has not done it since and the temp did not get as high as before,I checked all over the motor with the thermometer and checked the area around the plugs and got different readings and the motor seemed to have higher temps on the pass side.  I did see some bubbles in the radiator but it was still getting the air out since draining but will keep a watch out,with a bad thermostat can there be hot spots in the motor and still not overheat and this could have been happing forawhile but just noticed it today and the motor is a mid 80s 351-W. Anybody got any ideas on where to look if it starts doing it again.

[wayne petty]

jeff... do you have a radiator pressure tester?  some clear vinyl hose that will fit on the radiator adaptor once you have removed it from the hand pump....

take the belts off the engine.. so the water pump does not move when you start it... this will only take a minute or so of running... so overheating it is not a problem...

rig the clear hose so its open end can be hooked up by the hood...

fill the radiator to the top... squeeze the upper hose to get any air out of the system...  i like to squeeze the upper hose with the end of the vinyl hose in a gallon jug of coolant.. so it fills the clear hose part way up...


start the motor... watch the level of the coolant in the clear hose...

does it bounce up and down.. does it rise slowly... or does it blow out the top...

if it bounces...   you can stop... let it cool for a few minutes..

disconnect one spark plug wire at a time...  a quick start of the motor will let you know if you have found a leaking cylinder..   bad head gasket... cracked head.. cracked cylinder wall...

you might really want to loosen one head bolt at a time a fraction of a turn.. and retorque them.. perhaps just a little bit tighter..



other well equipped mechanics..  usually drivability techs have taken the pressure sensors from OBD2 cars fuel tanks... used them on a old radiator adaptor... hooked them to their hand held scope... disconnected the belts to remove any coolant flow.. and started the motor...  the tiny pulses of pressure can be picked up and converted to electrical voltage to be displayed on the scope..

the clear vinyl hose is just cheeper.. lets your eyes do the looking..


i am also taking that this engine has been together for a long time and has worked well ... there is not any chance that it is a fresh head install and one of the head gaskets was not installed backwards...    this has happened before..  and your description kind of sound like what happens...      cooler at the front of the head...  really hot at the back...

the coolant flow from the pump goes into the block.. around the cylinder walls...  through the openings at the back of the head gasket.. forward through the head.. then to the water crossover in the intake .. back through the bypass hose and again until the thermostat can open...    so you might want to check the bypass hose... make sure it is working and not clogged...

the bypass keeps the engine temps equal until the thermostat opens..

keeps the coolant circulating past the closed thermostat.. its a long ways from where the heat it made to the thermostat...

when one of the head gaskets is installed with the large openings at the front..  the coolant goes into the block.. then right up through the front of the head and to the intake crossover..   there is not enough coolant flow around the rear cylinders and the back of the head to keep it cool ... so the coolant will pulse... as it reaches the boiling point in localized areas...

[junkyardjeff]

Its a rebuilt motor but I dont know how much it was bored or much about it,the block and heads were provided by the builder and I am never going to do that again as I want to know what I am getting so I am going to build one myself with parts I get.  The motor has been togather for about 5 years and has about 6000 miles on it and this is the first time I noticed it,I did change the thermostat and took it for about a 30 mile drive and its not doing it but will keep watch.  It just has to stay togather long enough untill I get a Y block rebuilt,I am planning on doing a compression test and reading the plugs this week and see if it shows anything and will do the test you describe.

[wayne petty]

did you install the heads???  did you use hylomar on the head gaskets so we would not be having this conversation..??

if you did not torque the heads your self...

buy a pair of valve cover gaskets...

and what ever exhaust gaskets you need ...

pull the valve covers and the exhaust and retorque the heads...  its a lot cheeper to do that then it is to blow the head gaskets and damage the motor or leave you stranded some place needing to tow it back....

double check your click type torque wrench against a beam type torque wrench with a 15mm 12 point socket to connect the two first...


check it at 50 ... 70 and 100...

just ideas to keep you on the road....

wayne.... fixer of junk... almost every day...

[junkyardjeff]

The long block was assembled by the builder and the only thing I done was to put on a carb,exhaust manifolds and put in a distributor.

[junkyardjeff]

I was talking to someone about it and they suggested a slipping impeller on the waterpump and since I have to replace the balancer I am going to slap on a new pump while I am in there,took it for a long drive today and its still not acted up yet so maybe the thermostat had something to do with it but I am still going to change the pump to be sure its not the problem and they are not that expensive.

[wayne petty]

one thing jeff..

there have on some pump applications... universal directional pump impellers installed...

with straight fins..

these can pump water in either direction.  so you can run a V belt or a serpentine belt.. with the same pump... saves the manufacturer from needing to build 2 pumps...

but the straight bladed impellers really are not efficient..

can you take out a plug on the intake..  screw in a pressure gauge.. so u can see how much pressure is built up behind the thermostat at various RPMs...

leave it there and swap the pumps...

be sure to check the impeller..  for proper angles...    pushes the water out from the middle...

then check the pressure again when its all back together..

pressure in the block and heads  is higher than in the radiator do to the volume of coolant circulated and restricted by the closed thermostat and the small diameter of the bypass circuit...

if you don't want to put a pressure gauge...    and you have room..    take out the thermostat...   and the upper hose at the radiator..

aim the hose forward...   fill the radiator with the running garden hose..   rev the motor.. see how far the water shoots when you rev it.

do the same with the new pump..

these are just ideas to figure out whats going on...

[junkyardjeff]

One thing about the waterpumps on the sbf the plate on the back can be removed easily to check the impeller,I should have a gasket to put it back togather if nothings wrong.  I will check for a universal impeller and if it does have it I will try to find one with a correct impeller,it seemed to get hotter at idle and when revved up it would cool down so maybe there could be a issue with the pump so when I get the balacer I will run a bunch of checks and retorque the heads too.

[Bruce Dorsi]

....it seemed to get hotter at idle and when revved up it would cool down so maybe there could be a issue with the pump so when I get the balacer I will run a bunch of checks and retorque the heads too.

I don't know nuttin' about Fords, but could you have retarded ignition timing at idle?  

Does this engine have "performance" underdrive pulleys??  ......This can cause a problem because the waterpump is slower than on oem applications.    

As I said, I know nothing about Fords, but on SBC's, it is common for the waterpump to turn 25% faster than engine rpm.  .....Using underdrive pulleys, as claimed to increase horsepower, can causing higher temps at idle, and lower alternator output.

[junkyardjeff]

Stock pulleys and now that I found the balancer has slipped who knows what its timed at,I advanced the timing a little when I played with it the other day.