89 MJ Posted July 30, 2021 Share Posted July 30, 2021 As many of you know, my 4.0 has been overheating in my 89. It is a completely stock engine out of a 96. The motor had a new water pump installed, we can tell it is circulating coolant, and the temperature drop from the inlet side of the radiator to the outlet side is 30 degrees at idle when it is warmed up. But it still climbs towards 235+ just idling and 30 seconds of about 2600 RPM in neutral. There is no oil in the coolant, nor is there coolant in the oil, and it is not smoking at all. Is the 30 degree temp change too little of a difference? We are thinking that, if the 30 degree temp change is sufficient to keep it cool, then it may be leaking compression into the cooling system, causing too much pressure in the system and causing it to either push coolant out or circulate the coolant too quickly. Over the weekend, I plan to air up the cylinders to see if we are getting bubbles in the cooling system, but first I wanted to make sure the temperature change was acceptable. Link to comment Share on other sites More sharing options...
Jeep Driver Posted July 30, 2021 Share Posted July 30, 2021 Pull your plugs and read them. Link to comment Share on other sites More sharing options...
MiNi Beast Posted July 30, 2021 Share Posted July 30, 2021 How is the power band? Link to comment Share on other sites More sharing options...
Pete M Posted July 30, 2021 Share Posted July 30, 2021 where on the engine are you seeing the 235? Link to comment Share on other sites More sharing options...
89 MJ Posted July 31, 2021 Author Share Posted July 31, 2021 14 hours ago, MiNi Beast said: How is the power band? Without ever having a correctly running 4.0 to compare it to, it seems fine, it wakes up a little more in higher rpms. 13 hours ago, Pete M said: where on the engine are you seeing the 235? 235 on the gauge and near that on the head. It’s around 220 in the upper radiator hose. 14 hours ago, Jeep Driver said: Pull your plugs and read them. That’s the plan when we air up the cylinders. #1 looked pretty good, I haven’t gotten to the other 5 though. Link to comment Share on other sites More sharing options...
Pete M Posted July 31, 2021 Share Posted July 31, 2021 you've bled all the air out of the head, yes? Link to comment Share on other sites More sharing options...
89 MJ Posted July 31, 2021 Author Share Posted July 31, 2021 5 hours ago, Pete M said: you've bled all the air out of the head, yes? It’s been bled several times now. Update, the headgasket and head checked out and all the plugs looked fine. We are leaning towards the radiator being partially plugged. Link to comment Share on other sites More sharing options...
Pete M Posted July 31, 2021 Share Posted July 31, 2021 bled through the coolant sensor? with the nose pointed down? I hate to sound all naggy, but I've seen so many overheating cures solved by getting that last pocket of air out of the head. Link to comment Share on other sites More sharing options...
89 MJ Posted July 31, 2021 Author Share Posted July 31, 2021 14 minutes ago, Pete M said: bled through the coolant sensor? with the nose pointed down? I hate to sound all naggy, but I've seen so many overheating cures solved by getting that last pocket of air out of the head. Yessir. It was a real fun job. Link to comment Share on other sites More sharing options...
Pete M Posted July 31, 2021 Share Posted July 31, 2021 dang. Link to comment Share on other sites More sharing options...
Jeep Driver Posted July 31, 2021 Share Posted July 31, 2021 42 minutes ago, 89 MJ said: all the plugs looked fine. What does that mean? Link to comment Share on other sites More sharing options...
89 MJ Posted July 31, 2021 Author Share Posted July 31, 2021 1 hour ago, Jeep Driver said: What does that mean? Well, then all being consistent tell me that it isn’t pushing compression into the cooling system because, if it were, I would also assume that it would suck coolant into the combustion chamber making at least one, but probably not all 6, plugs look unusual. Link to comment Share on other sites More sharing options...
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