Headgasket or radiator??

[bullfisher]

After my motor reaches normal op temp it doesnt take long for it to start overheating. At first I thought it was a head gasket due to a little foam under the oil cap but no white smoke out of the tail pipe. Then I noticed my coolant fill/res. overflows and spews all my coolant. I did a rad. flush and seems to have good flow. could my head gasket blow in such a way that pressurizes my coolant system? I've replaced all caps, sensors and everything else that could be coolant related but the rad. its a 94 b4000 with about 12000 on a rebuilt motor. thanks for lookin, Joe.

 

[Big Jim M]

After my motor reaches normal op temp it doesnt take long for it to start overheating. At first I thought it was a head gasket due to a little foam under the oil cap but no white smoke out of the tail pipe. Then I noticed my coolant fill/res. overflows and spews all my coolant. I did a rad. flush and seems to have good flow. could my head gasket blow in such a way that pressurizes my coolant system? I've replaced all caps, sensors and everything else that could be coolant related but the rad. its a 94 b4000 with about 12000 on a rebuilt motor. thanks for lookin, Joe.

The foam under the oil cap is normal winter time condensation.. After a longer trip all the condensation evaporates and the cap should be clean again.
You replaced a bunch of stuff...did you replace the thermostat?
One way to see if the head gasket is leaking is to park with the radiator fill cap at the highest point of the engine/radiator.
Then with the cap off run the engine till it gets to operating temp with the radiator FULL TO THE LIP of the fill neck. While watching for bubbles the level may drop out of the fill neck..keep it full and if there are bubbles continusly in the neck that most times is the head gasket leak.
If you do have those bubbles don't waste time..repair as quickly as you can as running with low coolant will crack your heads very quickly.
Big Jim

 

[bullfisher]

If I remember right I tried this and just had it overflow out my radiator. The trucks been sitting a while and Im afraid to let it overheat again as it would happen to me and then I think I would fix it, only to find myself running A high temp again. My radiadtor seems to dump everything into and out of the overflow res.

 

[BRUTUS_T_HOG]

sniff the radiator fill neck and see if it smells like exhaust. and yes they can and usually do pressurize the cooling system.

my vote is to check the thermostat too. do this by starting the engine while cold and then as it warms up to about 200 degress your upper radiator hose will be hot and you shuold feel flow through it while squeezing.

does it cool down if you put the heater on max? this usually means a stuck thermostat.

also your fan clutch should be locking up when it gets too hot. does it overheat while you drive? or only at idle?

 

[bullfisher]

I've put two t stats in, it seems to only want to overheat when driving. If its a blown gasket then wouldn't you usually see white smoke?

 

[bullfisher]

OK went out and put a sniffin on the rad caps and it does smell a little exhuasty. DAMMIT!! I was hopin it wasnt a gasket. Thats not really somthing I want to take on.

 

[bullfisher]

Any other magical tests before I start forkin out coin on this thing??

 

[BRUTUS_T_HOG]

yes, $40 dollar block tester kit from napa. it is a blue fluid that turns yellow when you have a blown head gasket. that is a no doubt test, it confirms it

 

[bullfisher]

OK so I did the block test and bingo, head leak! So into it I go... any advice for me while im in there? Itsa 94 b4000.

 

[bullfisher]

Well that was fun, new headgaskets are in and it even runs! So im still trying to track down the source of this problem to begin with and Im still leaning towards the radiator. Now that the truck is running good I notice the temp guage will build to normal op temp and then suddenly dive back down towards the cold mark and do this every 3-5 minutes. As it builds the top rad hose gets firm and as temp dives back down the upper hose gets soft as if it needs pressure to force coolant through the rad into the water pump. this could be what the previous owner was having problems with, which eventually left me with head gasket issues. Ive replaced all temp sensers, T stat, water pump. Does this sound right to anyone or is there somthing im missing? and can I have the rad flow rate tested on the truck?

 

[BRUTUS_T_HOG]

that sounds normal. its the t-stat opening and closing to regulate engine temperature.

 

[bullfisher]

that sounds normal. its the t-stat opening and closing to regulate engine temperature.

Really? I've never had a rig that fluctuated temp before. Always thought the T stat stayed open once it reached op temp.

 

[Nhaz]

It tends to in the summer but during the winter a bouncing temp is fairly normal.