Engine Flushed Coolant - now leaking now engine getting hot.

[Jride]

I recently flushed my coolant because levels looked low and i had no idea when the last time it was done. When i opened the radiator, coolant level was not up to the top. Followed advice to do it on a slight hill to properly "burp" all the air out of the lines. I used the premixed Prestone 50/50.

I also replaced all the heater knobs and pull levers to get them sliding and working properly. Not because i use the heat, but because they were sticking out and it looked bad.

Cue all the problems. Sigh.

I'm now noticing (A) coolant leaking near the passenger side floor from the heater box assembly (B) the engine temp gauge is creeping towards the "H" at idle. Some days it chills somewhere around 60% of the way up. Other days 85%. This was not an issue before. I used a infrared laser thermometer to check engine temp. I'm getting about 220-230° closer towards the firewall (at idle) and cooler towards the front of the engine. For clarity, I am pointing laser at the black part of the engine under the valve cover gasket. But if i point the laser directly at the temperature sending unit I get 260°. Putting hands on the hoses it appears the coolant is cycling properly. The return hose towards the top of the radiator is hot, the radiator cap is hot, the host at the bottom of the radiator remains warm (not hot).

I'm curious to get your thoughts on a couple things:
1. What would now cause the coolant to start leaking when I never had a problem before? Anything I did with the knobs and levers that could cause parts of the heater box to open up?
2. Why would now the engine temp start creeping up?
3. Any thoughts on the engine temp readings I'm getting?
4. I'm considering changing out the engine temp sending unit.
5. I'm considering bypassing the heater box altogether (to address leaking coolant) by using a coupling to connect the intake and outtake hoses. This is a summer vehicle with no top or doors, so no need for heat.

Lots of questions, I know. Thank you, as always, for the insights and advice!

J.
1986 CJ7 Laredo , AMC 6-cylinder (AMC 258 i6 / 4.2l , i think).

 

[Manic Mechanic]

Sounds like the thermostat is sticking and you are not getting flow which would be why the lower hose is only warm. Also a leaking heater core could be due to having what's called a dirt seal plugging the hole. Now that you flushed it out it's now leaking.

The same thing happens with high milage engines when you switch from conventional oil to straight synthetic. Typically you end up with oil leaks.

You can by pass the heater core but there not hard to just replace. Same with the thermostat I always replace them whenever I do a flush it just cheap insurance.

 

[hole]

If it wasnt getting that hot before a flush, and the flush is all you did, crud has moved around.
1- Heater core needs to be replaced. Pulling the passenger seat will make this job easier for access.
2- Crud has likely migrated to the T-stat and is blocking proper flow
3-4 See number 2
5- No issues with bypassing

 

[jzak]

I would bypass the heater core, flush it again, and see if that does the job.

 

[Jride]

Sounds like the thermostat is sticking and you are not getting flow which would be why the lower hose is only warm. Also a leaking heater core could be due to having what's called a dirt seal plugging the hole. Now that you flushed it out it's now leaking.

The same thing happens with high milage engines when you switch from conventional oil to straight synthetic. Typically you end up with oil leaks.

You can by pass the heater core but there not hard to just replace. Same with the thermostat I always replace them whenever I do a flush it just cheap insurance.

Can I replace the thermostat without having to drain the coolant (again?) and if I choose to replace the heater box, can I do that without removing the dash?

 

[CJ]

Can I replace the thermostat without having to drain the coolant (again?) and if I choose to replace the heater box, can I do that without removing the dash?

You can easily replace the t-stat without loosing much coolant.
You do not need to remove the dash to replace the heater core. Just need to drop the heater box.

 

[Manic Mechanic]

You need to drain some coolant but not all of it