cooling system problem

[Portschy]

one of my customers has a 1992 1 ton dually 5 speed manual 4x2 non intercooled pickup, he makes his living hauling livestock all over the country, when the truck is at idle warmed up the heater hoses will go cold, i can bleed the system & they will get warm for awhile then go cold agian, driving the truck loaded or unloaded the temp stays in the normal range (170-190degrees on a mechanical gauge) while pulling but when i am going down hill & off the throttle the temp goes way up ( 240+degrees) & the heater starts blowing cold air. 2 t-stats have been tried,heater core has been flushed 3 times,entire cooling system flush, the radiator looks nice & clean & seems to flow good,a mechanic at a good diesel shop thought it may be a water pump problem so we replaced the water pump with the same results, i am confused as to what is the problem, a combustion gas test was done on the cooling system with no sign of leakage, anyone have any ideas??? , he had the injector pump replaced awhile back but the truck had the same symptoms even before that, any info will be greatly appreciated

 

[AlK]

1992 1 ton dually 5 speed manual 4x2 non intercooled pickup

1991. 5 and up all CTD are intercooled.

Does the fan kick in when the temperature goes up?

 

[bgilbert]

I'm trying to understand how the heater can blow cold air when the coolant temp reaches 240* . With coolant temps that high, and cold air being blown, to me would indicate a restricted or clogged/bad heater core. Obviously none of that hot coolant is being circulated through the heater core. OR, the vacuum operated doors within the heater core box/assembly are not functioning properly. One door is shut, so the blower doesn't blow air through a hot heater core, then you don't feel the hot air, also that happens when you turn the AC on. OR that junk vacuum operated water shut off valve inline with the heater core hoses is remaining closed or shutting off flow of hot coolant to the core.

-Also when going downhill and off throttle the temp climbs to 240* . . ? Not sure on that one, scratching my head too... where did you/he buy the two t-stats? Hopefully Cummins t-stats not Napa or worse. Install them correctly? Someone help me here, if a stat remains open, all the warm coolant will flow to the radiator? Or closed or I don't know! C'mon guys

 

[cerberusiam]

Check your vacuum pump and pressures. Sounds like the pump may be bad and until the engine winds up there is not enough vacuum to run the heater controls. I believe the hot water control is vacuum operated and if it is not open you will get no water circulating thru the heater core.



Exactly why the temp jumps to 240 off the thrttle and coasting is strange but it could have something to do with the heater circulation shutting down and a pocket of hot water not circulating. Where is your mechanical temp gauge plumbed in at?

 

[Portschy]

forgot to mention also that there is no valve in the heater hose,also we looped the heater hoses & eliminated the core & still the hoses will be warm at idle & then go cold

 

[Portschy]

the fan does kick in, the old one worked & when they installed the injector pump they put a new fan clutch on as well

 

[Portschy]

the engine is not the original he said it came out of a 91

 

[MMiller]

I had a tractor that was not making heat in the cab. I looked at the expansion tank, said in full range. I looked at the tank with the radiator cap on it(not on the top of the radiator) and there was coolant in it. I assumed the cooling system was full because it was not running hot. I had no coolant flow to the heater core. I ordered some parts and could not get to it the next day. Another mechanic went out and looked it over. He then started adding coolant to the system and got almost 4 gallons in the cooling system. THEN the heat worked. Just was air pocket in the heater because it was higher then the cooling system.



Not saying this will be your problem-but I was completely dumbfounded-because everything "looked" full.



Thats all I can add- very confusing why its getting hot on the downhills. Does the upper rad hose get hot when the gauge comes up to 240? Or is the upper rad hose staying cold? If it is then the t-stat is giving problems. When pulling hard my truck will build temp steadily going up hill, then as soon as the load is removed the temp will start to fall back to normal.



Michael

 

[bgilbert]

From my Cummins engine manual:

Coolant temp above normal:

Low coolant level- check/replenish coolant- locate the leak

Incorrect/malfunctioning pressure cap- replace w/correct rated cap

High lube oil level- check/drain to correct level

Loose drive belt on water pump/fan- check/replace belt or tensioner

Inadequate air flow to radiator- ck/repair radiator,fan shroud, fan clutch

Radiator fins plugged- blow debris from fins

Collapsed radiator hose- ck/replace hose

Malfunctioning temp sensor/gauge- verify gauge and sensor are accurate

Malfunction, incorrect or no t-stat- ck/replace t-stat

Air in cooling system- make sure fill rate is not being exceeded and correct vented t- stat is installed- ck for loose hose clamps- if aeration continued, check for a co

compression leak through the head gasket.

Malfunctioning water pump- ck/replace h2o pump

Incorrect injection pump timing- ck/verify pump timing

Overfueled injection pump- replace inj pump

Plugged cooling passages in radiator, head, head gasket or block- flush system and fill

with clean coolant.

Engine overloaded- verify that the engine load rating is not being exceeded.

 

[cerberusiam]

still the hoses will be warm at idle & then go cold

when the truck is at idle warmed up the heater hoses will go cold

I am confused??????





Cool or cold at an idle is not unusual as the engine doesn't develop enough internal heat to really warm things up and if the cooling system is efficient it will probably keep things cool.



Where is the temp gauge probe in relationship to the coolant flow? This might point to where the problem could be. If it is in the back of the head or engine this could be a problem because of the lack of coolant circulation there. Couple that with a thermostat working incorrectly or a bypass in the system it may a flow problem.



Looping the heater hoses is not a good idea because it just routes hot water around any cooling item and provides a less restrictive route than is nomally used. If I remeber correctly the heater water is pulled out before the radiator and dumped back in after it. The heater core and valves provide a restriction that may be used to keep the coolant flowing in the right direction and interrupting that could be problematic.



Once again it is important where the temp probe is located. Try moving it to different places on the system and see if you are seeing the same temp spike everywhere.





My 02.

 

[Philip]

Does the lower raditor hose have a spring in it?



If not it is most likely collapsing when in high throttle appilication= going up hill. When you go over the top and let off the throttle the hose opens and lets coolant threw. This would explain the high engine temps and the lose of heater output.

 

[JApplegate]

well on other trucks i have tons of problems with t-stats. suggestion, if possible, remove it, and dry truck. (don't think i need to explain what to do after drive) i went threw 8 on one truck. new products don't always work!. . learn that the hard way. but i also like philip's suggestion. seems right.

 

[cerberusiam]

If not it is most likely collapsing when in high throttle appilication

Guys read the post again. The heat spike is happening off the throttle on down hill runs not under power. Under power the temp is fine.



Could be a collapsing hose but it would proably be the top hose not letting the coolant flow.

 

[DPinkston]

the temp goes way up ( 240+degrees) & the heater starts blowing cold air.

This tells me it is a circulation problem. What would cause it is beyond me. Does it ever overheat just idling or only after pulling a grade then letting off the throttle? Perhaps it would overheat pulling a grade but the hill isn't long enough for the symptoms to show until after cresting it?

I don't see how it could be the upper hose as water is pushed through it. The only hose I have ever seen collapse is the bottom hose. Squeeze the bottom hose and make sure there is a spring in it for it's entire length.

Danny

 

[JStraw]

I'm so glad this problem was posted as I've developed the same symptoms over the past month on my '93 that has been driving me bonkers. I have replaced the upper and lower radiator hoses, changed the water pump, replaced the heater core hoses and vacuum control valve, changed the heater core and lubed all vacuum doors in the heater core / a/c box.



I did notice this morning while driving into work that as a car approach from behind to pass I saw what appears to be a steam/ water sray coming from the back. So, I'm guessing that I've still got a leaky piece of hose / pipe somewhere that needs hunted down.



Since I've gone this far, I may just change out the radiator.



Edit: Forgot to mention T-stat was changed. When I pulled the T-stat housing a piece of metal (looked like casting metal), about the size of a pencile eraser, was found on the block side.

 

[MMiller]

Sounds like you need to pressure check the cooling system. You need to track down a mechanic and beg, borrow, steal their cooling system tester. Wtih the truck cold you remove the radiator cap, then hook up the cap from the tooling . You then pump up the pressure in the cooling system with the tool, until you have 3 psi more then the cap is rated for. If the cooling system is not leaking then there should not be any drop in the gauge. If the guage drops then you get to start looking for a leak. When the h/g blew in my truck the coolant would get pushed out of the system, and then onto the exhaust causing the mist,steam, and a real underhood mess.



Michael

 

[cerberusiam]

Jstraw, check the engine oil cooler and the connections. These things are hooked to the engine and take a lot of vibration and ratling. Aside from the corrosion eating a small hole in the housing they can come apart internally and mix oil, coolant, and trans fluid in the automatics. They are a pain to see around and may have to be removed to be checked correctly but are a known failure point in the cooling system.



The rear cylinder comes with a built in flow restriction. Take a look at the way the cooler and heater lines are plumbed at it looks like a restriction in this area could cause a flow problem. If there is a restriction and you route the heater lines around the heater core it is possible the pressure under low rpm's is causing a flow problem and the circulation never gets to the back cylinder. These engines will do a fair job of thermal cycling without the water pump but it takes power to create the heat to get the cycle going and at an idle or off throttle the engine will actually bleed heat instead of retain it. Without enough heat the area around the temp sensor may not get enough flow and the temp will spike.

 

[JLEONARD]

Sounds like you need to pressure check the cooling system

Yes. That would be my next step and also verify that the cap is good.

Jay



edit... and one more thing I would check if not done already is to make sure the path to the overflow tank is clear... this causes all sorts of problems in the marine applications.

 

[JStraw]

Thanks guys I'll spend all day Saturday giving it a go over and replacing those little elusive hoses. Seems as if old age may be taking its effect on my baby. Good thing I got a big ol tub of Goop :-laf



Since I doubt I'll be able to borrow a pressure tester, can anyone give me a ball park price figure to get it done?



Has anyone replaced the lower radiator hose spring? If so, where'd you get it from? And, has anyone put a long spring in the upper? Would cutting the straight piece out of the upper and replacing with PVC be feasable. I'm beginning to not like rubber hoses.

 

[JStraw]

New observation. About 10 minutes into the ride home from work I saw the temp gauge do a sudden climb from 1/8th to about 6/8s of gauge travel in 5 seconds. It stayed for about 10 seconds then just as rapidly decreased back down. When I got home I had to add 1 gallon of fluid to the radiator and add some to the overflow which was bone dry. I couldn't see any steam or spray on the ride home or a wet trail coming from behind. I did notice a slight coolant smell and minor wetness from the hose connections to the heater core.



Can't wait until Saturday when I'll have time to dig deeper. Makes me wonder how tomorrow will go.