1999 Jeep Cherokee - cooling system problems

We’ve had a '99 Cherokee for about 5 1/2 years. It did great needing little maintenance for the first 5 years (give or take). Lately it’s developed cooling system problems. This began with a couple of rusted out freeze plugs which led to a nasty cooling system blowout with rusty coolant all over the engine.

(Being tight on cash we got used to the jeep running good and didn’t have the cooling system flushed for the first 4 years we had it – but the cooling system problem happened about a year later).

Our favorite mechanics replaced two rusted freeze plugs with rubber ones. The car runs ok, but ever since the work, it’s temperature can be sporadic – sometimes it runs hot. It’s been this way for about 4-5 months.

Two weeks ago the jeep overheated, (temp gauge showed hot, no coolant blowout), so my wife parked it and I took her to work in our other car. We picked it up later and I saw that the coolant reservoir was empty. I added water and we nursed it home (although the temperature spiked once). Just today, I decided to test drive it and found it running a little hot – I pulled into a gas station after about 2.5 miles and checked the reservoir bottle and found it empty.

I added water, drove it another 7.5 miles and checked the bottle when I got home - the water level was still full. I don’t see an obvious leak, but have the idea something is leaking. I’ve noticed moisture around where the valve cover joins to the engine block.

I’m wondering if anyone has a thought of what the problem(s) might be? (If I have a head gasket leak, is this a severe problem?)

At this point I’d like to get the leak repaired and sell the jeep if possible. It has a nice body and decent leather interior and is up to 120,785 miles.

Any thoughts on all that?

The phrase “moisture around where the valve cover joins the engine block” worries me as a possible intake leak.This is a “straight 6”? Hard to visualize a intake leak though,possible thermostat housing or sensor leaking.

For me a cooling system pressure test and a check for HC in the coolant is required.

I am not at all familar with your engine type (what ever it may be) so my comments are general.

Thanks for your reply. The engine is a straight 6 (4L, 2 wheel drive). I understand the thermostat housing leak but not sensor – are you saying there may be a sensor of some type that’s involved in the engine cooling system and it may be leaking?
Also, I get the idea of a cooling system pressure test, but what is the “HC” in the coolant I should check for?

Typically there are coolant temperature sensors screwed into the housing at this point,do you see any signs of leakage?

HC is mechanic shorthand for Hydrocarbon,if these enter the coolant as a hot gas they will cause the car to overheat,the way they can get into the cooling system is through a headgasket failure. The presence of HC in the coolant can be easily tested for (chemically) your mechanic should know how.

Thanks for the extra info. I’ll check for leakage around the coolant temp sensors with in the next day or two. Have a happy new year!