Overheating and no hot air 2000 Grand

[98Chero]

I just came back from a long trip, apparently I had a small coolant leak in my heater core. I caught it early and managed to limp home. I have changed the thermostat with a new one but cant get the heater to blow hot air. I have purged the air out of the lines but to no availe. I figured the high temp on my trip to have destroyed my old thermostat but the new one is acting the same way. currently my jeep overheats and dose not blow hot air out of the vents. i thought I have been down this road before but I might be missing a step ?

 

[TerryMason]

Assuming your heater fan works, no hot air from the heater usually means that the coolant isn't circulating, and no hot coolant is making it through the heater core. It could be a clogged system, or a bad water pump. It could also be a thermostat issue, if it's stuck closed, but I'd be surprised if two thermostats in a row did this.

Do both of the heater hoses to your heater core get hot when the engine is running?

Also, did you replace the heater core to fix the leak?

 

[98Chero]

Assuming your heater fan works, no hot air from the heater usually means that the coolant isn't circulating, and no hot coolant is making it through the heater core. It could be a clogged system, or a bad water pump. It could also be a thermostat issue, if it's stuck closed, but I'd be surprised if two thermostats in a row did this.

Do both of the heater hoses to your heater core get hot when the engine is running?

Also, did you replace the heater core to fix the leak?

The fan is working and I flushed the heater core with a high pressure water hose both ways and no restrictions ? both heater hoses seem to get hot, I was wondering if its my vacum opperated heater valve has stuck closed ? If I could get hot water to go thru my heater core I might try Bars Leak and see if it will fix my small leak till I can replace it with a new one.

 

[JPNinPA]

If your thermo stuck closed you would overheat within minutes . Blocked heater core can lead to overheating as this is the bypass for thermo and allows for proper circulation in the block.

You caught the leak. Did you fill and burp the system? If not it will lead to overheating until all the air is out of the system.

If you do have a vac valve be sure the vac line is attached and not leaking or cracked.
If you are still leaking you could temporarily bypass the heater ire with a loop to keep from losing fluid and gaining air in the system. I would not use any stop leak material.

 

[98Chero]

Ok bypassing the heater core makes sense now that its summer time. to the best of my knowledge I have burped all the air out of the system ? the engine runs rough now and i was wondering if i might have blown a head gasket causing air to enter the cooling system. at the end of the day I put my rear end of the jeep in a ditch to make all the air bubles come to the front of the radiater. this jeep is to clean to kick to the curb aka run it across the scales. any ideas are appreciated. I checked the vac lines and they seem to be all connected ?

 

[JPNinPA]

When do you overheat?


Over 35mpr
Under 35 mph
When ideling
Or after you shut off

Slow climb or immediate overheat?

 

[98Chero]

Lets say the engine was cold like this morning. I would start the 4.0 l and within 3 minutes the engine would be overheating. I bypassed the heater core and removed the thermostat.. same thing. If I let it cool down and restart the engine with the radiator cap off ( to add water) the water that was in it would start pouring out and alot of bubbles would also come out. Im at the point that I think it is a blown head gasket into the exhaust port or maybe a clogged radiator ? I cant rule out a bad water pump but the water seems to be flowing. with the engine still missing I am leaning more towards a blown head gasket, a compression check would confirm that. I have the tools and the time (thankfuly) to see this job thru.

 

[JPNinPA]

Lets say the engine was cold like this morning. I would start the 4.0 l and within 3 minutes the engine would be overheating. I bypassed the heater core and removed the thermostat.. same thing. If I let it cool down and restart the engine with the radiator cap off ( to add water) the water that was in it would start pouring out and alot of bubbles would also come out. Im at the point that I think it is a blown head gasket into the exhaust port or maybe a clogged radiator ? I cant rule out a bad water pump but the water seems to be flowing. with the engine still missing I am leaning more towards a blown head gasket, a compression check would confirm that. I have the tools and the time (thankfuly) to see this job thru.

If you warm it with the cap off and see a steady stream of bubbles either the head cracked or the gasket is gone. I'll see if I could post up a thread on checking for a crack. There are certain cast numbers that are prone to cracking.

By water I hope you mean a mix of coolant and water.. Water by itself boils near operating temp plus it becomes acidic. Don't mix coolant types.

 

[98Chero]

Thanks for the tip, I was just adding water because i didnt want to waste perfectly good anti freeze:idea: I still would be interested in any info you can provide on the engine troubles for that model.

 

[JPNinPA]

Casting 0331 are prone to cracking. Here are some pics. Water in oil?

 

[98Chero]

Thanks JPN for the pics and info. This morning I removed the upper and lower radiator hoses and flushed the radiator out. I replaced the hoses and clamps and filled the cooling system with a 50/50 mix of coolant and water. I left the heater core bypass tubing inplace and also no thermastat. I started the engine and it warmed up quickly and started overheating. the engine still has a small miss in it. I am beside myself what to do next ?

 

[98Chero]

Today I did a compression check and all the cylinders had 125 psi in them except #3 had 140 psi. The spark plugs all looked the same ( wore out) so I replaced them with new ones and nothing changed. I started reading my Clilton's manual to better understand the removing of the cylinder head. I am hoping that the intake manifold and exhaust manifold will come off as an assy and the rest of the cylinder head removal looks pretty straight forward. I got acouple quoates on the labor for relacing the head gasket at 350 to 425 not including parts. This is the first time I have removed a head on a 4.0 so any tips tricks or special tools needed would be some good info to know.

 

[JPNinPA]

Do you have water in your oil? Steam coming out of your exhaust? Smell like burning coolant in exhaust?

Typical signs from another forum: btw it was a cracked head.

Ok .. so I am pretty sure that my head gasket is blown or the head is cracked. Symptoms are:

Loosing coolant slowly (no visible leaks)
White smoke out of exhaust (sweet smelling)
Misfire in Cylinder #
Low compression in Cylinder #


From your compression test it is unlikely a head gasket. The numbers are low but above minimum spec. The delta isn't way out. This low compression could be carbon build up on the valves, leaky valves or ring blow by. Did you do this test with a cold engine or a hot engine?

 

[98Chero]

I tested it with a cold engine. I am completely stumped on what to do next? The engine got hot and gets hot everytime i run it. I thought about replacing the radiator and water pump but i dont think it will fix the miss in the engine.

 

[JPNinPA]

Compression is best measured with a warm engine that was kept at temp for 5-10 min minimum.

 

[TerryMason]

This sounds just like you, no heat and all.

 

[98Chero]

Thanks for the Vid ! its worth looking into . the grand has almost 300.000 miles on it and Im sure its the orignal water pump. I will post my findings on here, it might be a couple days tho because we are in a rainy period and my shop is filled with junk lol.