MP World Hemi block P5153942. The other number above that is 0803049A946. This block was sold by Summit. It is a mild 10.5:1 540 with a 250* FTS cam. The stroker kit and cam came from Ray Barton. The heads are MP Edelbrocks ported by MCH.

The engine takes several minutes to warm up with a thermostat. And I have tried several different ones, both 160* and 180*. A few minutes after the temp gage stabilizes, it starts climbing until it pegs. Then sometimes it stays there until I shut it off and let it set a few minutes. And then sometimes it drops back down to normal.

Now comes the weird part. After the temp drops to normal, I can drive it all day long and it does fine. I think that the issue is on the passenger side which is where the temp sender is located. As the engine warms up the passenger side is 10* to 15* ahead of the drivers.

The outside of the engine does not get above about 190* on the pass side, but the radiator will be spewing and you can hear the water inside the engine bucking. While the drivers side shows 130* or 140* on the outside of the head.

I know there were machining issues on the pass side of these blocks and I have pulled that front core plug and water pump housing and cleaned up that area as much as I can. It does appear to be a bit obstructed in that area, but not blocked.

I am resigned to the fact that I will probably be pulling the engine out and apart. I just want to be sure that there is nothing I can do with it in and together. Or to make sure that if I have to pull it, that I get to the bottom the issue.

I would really appreciate any insight into this. And I apologize for the length of this post.

Thank you

You should be able to pull the cap when its warmed up and watch the water circulate. Has to be a circulation problem doing what it is doing. Antoher thing is put the sender in the pump, might make the problem go away lol!

There is plenty of flow. And again, after that initial temp spike, I can flog the crap out of it, and it stays cool.

The temp sender is mounted in the usual position on the pass side of W/P housing. I guess I don't understand what you mean by putting the sender in the pump. And I don't understand how doing that would stop the water from bucking inside the engine and spewing with rad cap off.

Ok sender is in normal spot, I took it as you had it in passenger side head or something. You can let the coolant circulate at idle, yes it will push some out and you will have to top it off before you put the cap back on. Only reason I brought it up is the temp spikes you are describing point to blockage. I cant think of what would cause blockage/ temp spike, then go away other than a bad stat or major air lock somewhere.

I would make sure there is no air in the system. Sounds like possibly an air pocket. Have you put a pressure checker on it?

Sounds like a flow problem to me, but the fact that it goes away and it fine is the weird part. I've had two similar problems with 440 blocks that were the 76-78 motor home blocks. They have the cooling holes drilled in the deck down at the bottom row of head bolts and are designed to match up with heads with the same holes. In both cases, we did not have the correct heads with the holes so circulation was impeded. They would get hot and boil inside the block. You could hear it. We changed to the matched block/head combo and cured the problem. You might check your heads too.

After the temp drops to normal, I can drive it all day long and it does fine.. This is what makes it interesting and seems to rule out anything "serious"

Sure sounds like you have an air lock, but I would try some more detective work before tearing into it..

Running without a stat

Make sure you have a shroud and rad is sealed good to rad yoke

Put a fan in front of rad and let car run see what happens

Make sure you have the right pulleys

Any chance you are using a 440 source wp or wp housing, they have had issues, also some of the blocks had a mismatch between the front coolant holes in the deck and the head, but I have only heard of them being oversized, not small.

I need to try running without a stat. I haven't done that yet. Surprisingly, it takes a long time to come up to temp. It will be interesting to see how long it takes without a thermostat. The housing and water pump came from Mancini last winter. And the head gaskets are Cometics spec'd by Ray Barton for this combo.

It is definitely a water flow problem and seems to be on the passenger side. It acts to me like it has little or no water flow somewhere in the pass side block or head at start-up. But has flow after it warms up. The stat may play a role in that somehow.

I am sure that the 50/50 water/antifreeze mix is boiling somewhere inside the block or head on the passenger side. Then finally pushes out past the temp guage on the pass side of the WP housing. Which I believe explains what is happening when the temp guage pegs and the water spews out the rad cap while the pass head, block, and pass side of the WP housing just show 190* or so on the temp gun.

The hot spot is more toward the middle (or maybe rear) of the passenger side of the block or head. Given what I see happening, I don't see that air flow is the issue. Never say never, but the evidence seems to point to a lack of water flow or maybe an air pocket somewhere on the pass side. But I don't think that the entire pass side is starved for water given that the front of the pass head, while sometimes warmer than the drivers one, is not over heated.

I would try to fill the system with a air/vac tool just to make sure that it isn't an air pocket. There are a few of them on the market and most all tool trucks sell them.

Gus

This is what I use.

Interesting update:

I spent the afternoon with the car. Pulled the thermostat out first thing. There was so much water flow that I couldn't rev the engine much without throwing water out with the rad cap off. Excellent water flow.

It was very slow to even get to 150*. But I ran it a good hour or so and blocked some of the radiator air enough to get the temp to 180* or 190* and then pulled the cardboard so that it went back down to 150* or so.

No temp spikes or thumping or blow outs.

Hmmmmm.

So I'm guessing that the pass side comes up to temp first and maybe gets too hot before the thermostat opens. Maybe so hot that it creates a steam pocket. I always drill a hole in the thermostat, maybe I'll add another hole or two.

Now I wonder if that pass side is lean on a cylinder or two. The tubes are roughly the same temp when I check.

More testing in a day or two. I'll drill more holes in a thermostat and see if that allows enough water flow to keep the pass side from overheating while it warms up. And also monitor the tubes on that side for problems.

I think you previously created an air pocket over there. Did you drill two 1/8" holes in your thermostats? I always do this and never have an issue with trapping air as the holes allow all the air to the top of the system when filling.

I have 800 miles on this engine. This overtemp problem has happened many times. And as I stated in the previous post, I always drill a hole in the thermostat.

Sorry, missed that... Well, it sure seems that, as you removed the thermostat and the problem disappeared, that somewhere in that system is what is giving you headaches.