Excessive Pressure in Cooling System?

[Z-24CHEVFAN]

Hello. I have a 1985 Ford F-150 (300 6 cyl. engine). While driving to work the other day, the engine began to overheat and eventually stalled. After looking underneath the hood, I found that the lower radiator hose had come off. This led to all of the coolant leaking out. I replace the hose, tightened the clamp, and replaced the anti-freeze. All was well for a couple of short trips, but after driving about 3 miles today, I parked it in the driveway and heard an actual explosion underneath the hood with the engine off. The lower radiator hose had blown right off, leading to a coolant mess again. During drivng, the temperature gauge remained in the normal range. There is no visible coolant traces on the engine oil dipstick. The thermostat appears to be working, as I have heat. The engine seems to run too well for a head gasket problem. Does anybody have any suggestions? Thanks.

[mechhound]

When you say you relpaced the hose, do you mean with a new one? Did you use a new worm type tin band type clamp?(this is the type most auto jobbers sell, these are the best) If you tried to reuse the double wire type clamp that may have been stapled to the original hose, I have had the same experience as you, a blown off hose. At any rate, I think your last incident was from the hose not clamped properly. Just my 2 cents.

[Z-24CHEVFAN]

Originally Posted by mechhound

When you say you relpaced the hose, do you mean with a new one? Did you use a new worm type tin band type clamp?(this is the type most auto jobbers sell, these are the best) If you tried to reuse the double wire type clamp that may have been stapled to the original hose, I have had the same experience as you, a blown off hose. At any rate, I think your last incident was from the hose not clamped properly. Just my 2 cents.

Hi mechhound. Thanks for the reply. Admittedly, I re-installed the disengaged end (radiator nipple side) of the old hose. I believe that I had replaced that hose before about 4 or 5 years ago. Yes, the clamp was the worm gear type with the serated band, not the original OEM-type Motorcraft wire clamps. I can replace the hose with a brand new one and even double clamp it, but I am still worried about the way that it blew right off the radiator, even after the engine was turned off for a few minutes. It was like there was tremendous pressure built up. It sounded like a stampede of 1000 elephants when it happened. The whole neighborhood shook. Do you think on a little 300 6 cyl. that it could be leaking combustion pressure into the water jacket, or just a poorly-sealed and weak hose? I read another thread on this F-Series forum were the owner had a big Ford diesel with this problem, but with my luck I'd pull the head and find nothing wrong. I'd rather avoid a project like that if possible anyway.

[cujafish]

put in a new thermostat anyways - they are very cheap
they stick creating too much pressure which means yes u will still have heat if the thermostat doesnt work
they have summer, winter, and all seoson
the all season are good for about 2 years - sucks

they should be replaced regularly on this vehicle

there is a belt that turns your water pump
pump = average 40 - 60$
tighten belt
if this not work then change your water pump

because if your thermostat is sticking it can fuck the water pump up

all the luck that you dont have to take the radiator and fan out to get at the water pump

[Z-24CHEVFAN]

Thanks, Cujafish. I am going to try replacing the thermostat because it makes sense. If the water pump is constantly drawing in water/creating pressure in the water jacket, then if the thermostat is sticking closed a bit, it'll build up pressure. When the pressure gets too high, the only way out I guess is through the lower hose fitting. I also bought the NAPA block tester kit
(7001006). You stick it in the radiator filler neck and draw in air from the top of the radiator with the engine running. If the fluid turns yellow, you have exhaust seapage into the water jacket. I am hoping it is the thermostat, though.

[rrousou]

Possibilities: head gasket, cracked cylinder head, or crack sleeve in the block. there's a tool that you can hook up to on the rad to determine if it is a combustion leak.

[ModMech]

The "300-6" is NOT known for blowing headgaskets even when serverely abused (overheated etc), and a cracked head I have never seen in over 30+ years of working with this specific engine.

It is completely possible that the hose comming off the first time was just a fluke, and that when the radiator was refilled with coolant there was air trapped in the system. That is very common especially with aftermarket (non OE) thermostats that do not allow the air to bleed out.

I would:

1) Replace lower hose and clamps
2) Replace thermostat with OE
3) Fill system, run with radiator cap OFF until all air has been bled out, and watch for bubbles in the radiator when engine warms up fully. If bubbles "just keep comming" then you do have a headgasket or cracked head. I would be shocked if this were the case.

[MT-2500]

Originally Posted by Z-24CHEVFAN

Hello. I have a 1985 Ford F-150 (300 6 cyl. engine). While driving to work the other day, the engine began to overheat and eventually stalled. After looking underneath the hood, I found that the lower radiator hose had come off. This led to all of the coolant leaking out. I replace the hose, tightened the clamp, and replaced the anti-freeze. All was well for a couple of short trips, but after driving about 3 miles today, I parked it in the driveway and heard an actual explosion underneath the hood with the engine off. The lower radiator hose had blown right off, leading to a coolant mess again. During drivng, the temperature gauge remained in the normal range. There is no visible coolant traces on the engine oil dipstick. The thermostat appears to be working, as I have heat. The engine seems to run too well for a head gasket problem. Does anybody have any suggestions? Thanks.

Check that Radiator cap.
If it is working right there is no way it can build to much pressure.
MT

[ModMech]

MT, radiator caps are spring pressure caps, it is VERY unlikely that a spring would suddenly have more pressure. More likely it would break or become very weak causing excessive coolant loss from the overflow.

What he has sounds like localized hot-spot boiling of the coolant, commoly caused by air entrapment.

[Z-24CHEVFAN]

Hello. To follow up on this, I changed the thermostat and lower radiator hose/clamps. I used propolene glycol this time in case it blows again because it is environmentally friendly. I ran the engine for a while with the cap off. The temperature gauge acted normally. I then used the Napa block tester (p/n 7001006) as directed. The test fluid remained blue, which indicates that there should be no combustion leak into the water jacket (turns yellow when exhaust gases aree present). I drove it for a short distance. So far, so good. I did notice before (when it was blowing the hose off) that the truck was running a bit hotter than usual. I decided to test the old thermostat in a pot of boiling water. It did open eventually, but took a while, and I know the water temp. was higher than 195F. I have a feeling that it was the thermostat. I'll take progressively longer trips, monitor the temp. gauge, and keep auto forums informed. Thanks.