I have a slow coolant on my 1988 b250 somewhere. Still drives great just, have to top up the coolant about a cup once a week. I’ve already replaced the thermostat, upper and lower rad hoses. No coolant mixing in the oil or oil in the coolant.

I hooked up a pressure tester to the rad and got it to 15psi, immediately started going down slowly in pressure and lots of coolant drops coming from the top of the water pump/bypass hose area. Hard to see lots of stuff in the way. going to try removing things to get a better view.

Hopefully I’m on the right track here, any input and tips would be much appreciated! I will update as I progress.

 

The bypass hose itself is a likely candidate.

 

Well it looked like the bypass hose. Once I removed the air injection and brackets, I saw it was leaking out of the top water pump gasket. It took awhile but I finally got everything removed and at the water pump bolts. First bolt I loosened caused coolant to start leaking out of where the timing cover meets the block. I pulled the water pump. Gasket failed in a few spots. Pulled the timing cover and more gasket failure. It failed on one of the bolt holes that went through the water pump then timing cover and into the block, thankfully leaking the coolant externally rather then internal.

Put on new timing chain and sprockets, new gaskets for timing cover, new water pump with gasket. New bypass hose. Got it all back together. Started it up. Running good. 2min later coolant leaking! Oh no. It was coming out of the bolt hole for water pump. Damn.

first time it took me all day to access the water pump, this time 45 minutes! My mistake was I didn’t squirt gasket sealer down the bolt holes nor did I wait 24hrs for the gasket sealer to “set”. I believe there is a water jacket through timing chain cover and water pump? That didn’t seal, I think. New gasket and a squirt of sealer down every bolt hole and 24 hours later. Success! Started up and ran well. No leaks. Warmed it up. All good. Took it for a drive and it running even better now. Pretty stoked, I’ve never done a job like this before on a vehicle. This site was extremely helpful, lots of info on the 318 here .plus I have the factory manual. Anyway
Don’t for get those bolt holes!

 

Nice job. Chrysler products have been like that for a long time with the sealer on the bolts deal

 

Good job, but just and FYI for you. Only lightly coat the bolt threads with sealant and never "squirt" sealant into a bolt hole. The reason for not doing it your way is as the bolt goes in it pushes the sealant to the back of the hole and can actually stop the bolt from going in as far as it should, or worse yet, the extra torque need to overcome the sealant blocking the bolt can cause the hole to strip out.