429 Overheating

I have a 1989 Ford 750 with a 429 in it 16,000 miles , so it’s a pretty low milage truck. Truck runs fine for a year then a few weeks back it overheats. Temp gauge inside the
cab climbs and it overheats again.

We replace the radiator cap 190 degree- same overheating issue

We replace the thermostats (two)- same overheating issue

we check the thermostats - they work fine 13 PSI

we check the timing- dead on

We take the radiator down and have it checked - radiator shop says it’s clogged

We install a new radiator- still over heating

While were in there we replace the water pump, no signs of junk but we put a new one in.

still over heating

we buy a T filler and fill the system up on the heater hose, we use a burper funnel- a few small bubbles both nothing crazy

We check of exhaust gas in radiator fluid- negative

Note engine ideas very smooth.

We do a compression check - all cylinders within a few precent

Checked plugs they look good

We park the truck on a incline fill it up give the engine a few blips to 2-3 K

Truck ideas for 15 minutes and the water in the upper hose near the thermostats start to boil

We use a laser and read 170 on the upper hose 75 on the lower hose- like no waters flowing through. it then boils over.

We check the radiator put the hose in the top end and watch water flow out, so it’s not clogged.

We do a block flush for three days

We test and repeat the boil over

We then replace the water pump again

Retest and it boils over top hose 170 degrees bottom hose 80 degrees.

Seems like that bottom hose should be a lot warmer


mystified. Any suggestions?

Water doesn't actually boil till 212. 50/50 shouldn't boil till well over 240.

Are you over filling the radiator? Are you using antifreeze or 50/50 or water?

I have my own running warm issues so I feel your pain.

Personnaly I like to run less antifreeze as antlfreeze is actually not as good a coolant as water is  so I run 30-70  40-60.

I think whats happening is that once the thermostats opens the  coolant just boils as it passes the thermostat

radiator fluid level is at proper level

crossram wrote:Personnaly I like to run less antifreeze as antlfreeze is actually not as good a coolant as water is  so I run 30-70  40-60.

I think whats happening is that once the thermostats opens the  coolant just boils as it passes the thermostat

radiator fluid level  is at proper  level  

Second question everyone on here will ask is do you have a radiator shroud.

FSU_Bronco wrote:

crossram wrote:Personnaly I like to run less antifreeze as antlfreeze is actually not as good a coolant as water is  so I run 30-70  40-60.

I think whats happening is that once the thermostats opens the  coolant just boils as it passes the thermostat

radiator fluid level  is at proper  level  

Second question everyone on here will ask is do you have a radiator shroud.

Seriously?

It's a 750 truck with a huge radiator and plenty of air flow, not a Mustang.

Not a 150, 250 or 350 it's a 750 as in Big

crossram wrote:

FSU_Bronco wrote:

crossram wrote:Personnaly I like to run less antifreeze as antlfreeze is actually not as good a coolant as water is  so I run 30-70  40-60.

I think whats happening is that once the thermostats opens the  coolant just boils as it passes the thermostat

radiator fluid level  is at proper  level  

Second question everyone on here will ask is do you have a radiator shroud.

Seriously?

It's a 750 truck with a huge radiator and plenty of air flow, not a Mustang.

Not a 150, 250 or 350  it's a 750    as in Big

So does it have a shroud or not?

Where is the second thermostat located? I'm guessing in the lower hose or something? Take it out and see what happens. Maybe it's not seeing enough temp to open and let coolant circulate?

Also, does it have a shroud?

SLord82 wrote:Where is the second thermostat located? I'm guessing in the lower hose or something? Take it out and see what happens. Maybe it's not seeing enough temp to open and let coolant circulate?

Also, does it have a shroud?

both are next to each other top of manifold

crossram wrote:

SLord82 wrote:Where is the second thermostat located? I'm guessing in the lower hose or something? Take it out and see what happens. Maybe it's not seeing enough temp to open and let coolant circulate?

Also, does it have a shroud?

both are next to each other top of manifold

They are both opening at the same time will when you boil them?

Probably not your problem since your motor is overheating at idle but is your bottom hose collapsing from the water pump? Lower hose have the ribbed spring enforcement? I'm watching this thread closely as my 429 runs warmer than most fellas I read about.

Cebu wrote:Probably not your problem since your motor is overheating at idle but is your bottom hose collapsing from the water pump? Lower hose have the ribbed spring enforcement? I'm watching this thread closely as my 429 runs warmer than most fellas I read about.

What he said.

Ive had the spring in the lower radiator hose break and shift causing the hose to collapse on 2 different occasions.
Start it and get it warm. Then rev the motor while watching the hose.