Coolant leak at the back of the head

[Dumb A]

Help from the wizards please. I have a coolant leak dripping from the back of the head running down the bell housing. I stuck a small mirror back there and I see a sensor bubbling around the ceramic center. I tried to identify the sensor in the service manual, no joy. This sensor is screwed onto the head, water jacket at the aft end of the head between the head and firewall, thanks!!!

[Dieselfuture]

Sounds like someone added a sensor there, I don't have any sensors in that location. Maybe it needs to be resealed with some teflon tape.

[Dumb A]

It was difficult to see, I used a mirror and lite from the driver's side. I will have to get a better look at it tomorrow. I'm going to remove the rocker cover to see if this helps and run the valves while I'm there. It looks like it was leaking from the center of the sensor? 

[IBMobile]

5 hours ago, Dumb A said:

I see a sensor bubbling around the ceramic center.

The sensor is bad and needs to be replaced.  If the sensor isn't needed then remove and put a plug there;  to seal the threads I use Permatex no. 2 or Rectorseal no. 5.

[dripley]

Are you sure its coolant? Are you replacing any coolant for loss?

[Dumb A]

The sensor is bad and needs to be replaced, yes and I'm going to put a plug in its place, sensor was evidently to plug the npt threads. 

4 hours ago, dripley said:

Are you sure its coolant, yes I'm sure it coolant and yes I have been replacing it. 

My next question is the port with the npt threads on the back of the head, water jacket or intake manifold? Because I saw air bubbles escaping around the ceramic on the sensor. The coolant leak may be coming from the freeze plug and wetting the sensor??? Thanks for your input.

[dripley]

I don't know of any sensor on the back of the engine from the factory. Does this sensor having a wiring harness attached? There is a return fuel line on the head and then freeze plugs on the block below that and I have heard of those springing a leak occasionally. 

[Dumb A]

I don't know of any sensor on the back of the engine from the factory...

 

your correct, I think someone has screwed that in there rather than a plug, why I don't know... I don't know if that is a coolant passage that it screws into or part of the intake manifold though. I'm guessing it is leaking from the freeze plug next to it, on the head. The coolant is coming from above the head gasket for certain. I took a long stick wrapped with many papers towels from the driver's side underneath and dried off the back of the head and block. I could then see coolant weeping down the back of the head to the head gasket and down onto the block. So I'm certain is coming from the head. Has anyone ever cut a hole in the firewall to access this area, I am going to look at that possiblity. Maybe moving the engine and transmission forward, possibly... I may pull the engine and replace all the plugs, pan gasket, front and rear seal, pilot bearing upgrade to the heavy duty one. I have the time to do it...

[dripley]

The PO might have put a plug in place of one that was leaking. Not a happy place to work back there.

[IBMobile]

To cut a hole in the firewall you'll have to remove the dash and HVAC assembly.  Push come to shove, you can see the back of the head real well with the trans removed.

 

Are you pressurizing the cooling system with a coolant pressure tester?  This may aid you in finding the exact position of the leak.  You can rent one for free at O'Reillys.

https://www.oreillyauto.com/detail/b/evertough-4771/tools---equipment-16488/rental-tools-16837/rental-tools--air-conditioning---cooling-19163/12095d53bcad/rental-tools-evertough-radiator-cap-test-kit/67085/4700282

 

[ddmk6]

At least yours looks to be a makeshift sensor leaking.  When mine leaked back there it took a new head to fix it.  Original was cracked.

[Mopar1973Man]

In my case around 350k miles I had my head curl some and the head gasket started to leak near the rear of the head on the passenger side of the block.

[Dumb A]

Good info, I will get a pressure test tool and give it a test. 

There are oil leaks around the engine, dirty as can be. I haven't wanted to steam clean it as I'm concerned about the electronic components not working afterwards. Would it be smart to pull the engine, reseal it, clean it, replace all freeze plugs, bore the flywheel for the larger pilot bearing. This is if I find the freeze plug to be leaking. Is it a lot more work to pull the engine rather than the transmission. 

[Mopar1973Man]

I power wash engine all the time it will not hurt anything... Just let the engine cool down below 140*F before starting. You can spray down everything just don't spray directly at plugs or connectors. Everything can get a bath. 

Edited January 17, 2021 by Mopar1973Man

[Dumb A]

Thanks.... The fellow who sold me the PCM was the one who said don't power wash/steam clean these units as it can kill the PCM, ECM and sensors. Made good sense but I don't like having a dirty engine and engine compartment. So off to the cleaners I go, then pressure test.

[Mopar1973Man]

2 minutes ago, Dumb A said:

The fellow who sold me the PCM was the one who said don't power wash/steam clean these units as it can kill the PCM, ECM and sensors.

 

You can spray them off just keep your wander back at least 1 foot from modules. Never had one problem with power washing vehicle ever. Most of the time I look under the hood before rolling in the shop if the truck is greasy or super dirty it will get a full power wash job before starting. Why work on a vehicle with dried mud falling in your eyes or having to reach down into the engine bay and get greasy all the way up past your elbows? Why? Heck I power wash and clean them up that way I don't have to wash for hours get the greasy mess off me and the customers always love to see a clean engine afterwards. 

 

Just don't put the spray nozzle again any connectors other than that you'll open up the connection to blow dry the connector and add di-electric grease. 

[Dumb A]

That's what I normally do, keeping my engine compartment and vehicle clean. That way you can see new oil leaks and things going wrong, hopefully keeping ahead of problems...

[Mopar1973Man]

Exactly. 

 

 

[Doubletrouble]

 Anyone have a favorite degreaser to cut through the oil. My engine isn't bad but I would like to degrease it to detect leaks. I have one oil leak now around the oil cooler where the oil filter spins on. Had a couple loose bolts. Not to mention the oil on the radiator. I haven't done the crank case vent mod yet.

[Mopar1973Man]

Two strongest I've found is "Home Depot Industrial Degreaser" and Common Household Oven Cleaner both are acid based so do leave on aluminum parts it will blacken them. Don't get on your skin it will burn up for sure. I typically use them at 100% strength and my soak time is limited to just at the tops of 1 to 2 minutes or less. 

 

Crud... HDX brand is no longer sold but the Zep brand is... Still works just the same.

https://www.homedepot.com/p/ZEP-1-Gal-Fast-505-Degreaser-ZU505128/202790160