Running normal at idle but cold at throttle

[MORGAN 34]

With a new Dole style thermostat and a ball valve on the bypass side I can get the motor to run at 155-160 at idle speed, but when I throttle up to cruising speed (sorry I don't have a tach, but I would say about 1800 rpm, the temp drops to 130.


I was originally running hot, so I did the following:
New impeller
Acid flushed the block and manifold
Pulled apart the hot exhaust section for inspection
Replaced the temp sending unit (that's in the same location as a later motor. Someone drilled and tapped the head)
Replaced the gauge (both gauge and sending unit are SW and are the correct pairing). Replaced the hoses.
Did a leak down (about 19 psi) of the cooling system and lost nothing in 10 minutes.
Did a compression test (119 on 3 of the cylinders and 125 on the last). I assume I have some carbon build-up on the 4th).

Anybody have any ideas? I'm at my wit's end. At least I know I have a strong motor.

TIA,
Chad
1967 Morgan 34

[hanleyclifford]

opposite problem

You seem to have the reverse situation most find themselves in. When you throttle up I assume you have the bypass valve open, otherwise you are defeating the purpose of the thermostat.

[MORGAN 34]

No, I just have it about half open (or half closed if you are a pessimist)

If I need to adjust it every time I change throttle, what good is a thermostat? I don't want to have to take my steps off 3 or 4 times each time I go out. Is that what everybody is doing?

[hanleyclifford]

Could you possibly post a picture of your thermostat and bypass installation?

[Dave Neptune]

Wow

Chad, something is amiss, I don't have that much variance and I don't use a thermostat at all. Perhaps your deflector is'nt pointed the right way or is even missing. Some of the thermostats operate the bypass and if they do not have the proper housing the bypass will not close down enough and force the water through the block, instead it still takes the bypass route causing the engine to get warmer when making power with the thermostat open.
If your impeller was complete when you replaced it I doubt the it would be the culprit, but you could have shook someting loose and it is wedged in the bypass area of the thermostat.

Dave Neptune

[marthur]

You are getting a lot more cooling at speed. That makes me wonder first about your water pump. Check the size of the Cam Shoe and check the water output at idle.

[MORGAN 34]

I'm not sure what a deflector is, but the housing and thermostat are new and from Moyer. It's the dole style since I have an early model enging.

I think my water pump is fine. Emphasis on "I think." It's difficult to ge the impeller in. I have to twist as I align the shaft and the top 3 blades are twisted against the housing. Does that help?

[Kelly]

Here is an excellent picture of a new impeller installed in an Oberdorfer pump (thanks to Michael Arthur and his excellent web site here)

Notice the bent lobes on the impeller- this is completely normal and allows the pump to do its job correctly. The cam shoe is specifically in place to help bend the lobes and needs to be replaced if worn with use.

[Dave Neptune]

deflector

Chad, the deflector is inside of the water jacket and directs the water to flow around the cylinders. They will make a differance. It is part of the "Tee" fitting (side plate) where the water is carried into the block. Many engines have had them MISTAKENLY replaced with a NPT pipe Tee and they do not direct the water.

Dave Neptune

[Baltimore Sailor]

Does anyone have a picture of the diverter and tee so that we can see what we're talking about?

[sastanley]

water jacket side plate

The cap goes on the backside of the water jacket "T" fitting.





I can't remember if you have to drill both holes or only one, but you screw the cap onto the fitting, mark which flat of the hexed cap faces toward 4 o'clock, then remove it and drill a hole in that flat (& also in the end of the cap if it isn't there). Then it spews water out the end of the cap towards the opening between cyls 2 & 3 to get some water over to the valve side, and then the 4 o'clock hole shoots water toward the aft end of the block.

[Baltimore Sailor]

Interesting. The cap doesn't come pre-drilled, eh?

What diverts the water within the t-fitting? Just the pressure of the thermostat being closed? That would make sense, given the action of the ball valve to improve water flow into the jacket, especially if the little holes in the cap are clogged with goo.

[MORGAN 34]

Chad, the deflector is inside of the water jacket and directs the water to flow around the cylinders. They will make a differance. It is part of the "Tee" fitting (side plate) where the water is carried into the block. Many engines have had them MISTAKENLY replaced with a NPT pipe Tee and they do not direct the water.

Dave Neptune

I have an early model so I don't have that. I have the crossover from the block to the manifold and to the thermostat (Dole style) and either back through the engine or out depending on temp.

However, I have never taken the side plate off. I wonder what it looks like inside there.

[sastanley]

BS, you can't pre-drill the hole because each cap fits on each "T" slightly differently as they are NPT threads..one may spray down at 6 o'clock, or one might spray straight up.

Since they are brass, the work is easy.. 1/4" drill bit with the cap in a vise on the bench was no problem. I have a drill press now though, so it would be even easier - Since the holes are 1/4" I think the volume of water is sufficient to come out of both holes in the cap with some force. From what I've read the earlier diverters would rust away, gunk up, corrode, whatever. I don't recall anything on the end of my "T" when I removed the plate last winter...but I had lots of Chesapeake mud in the block.

Too bad we don't have a see through A-4 block. That would be fascinating to watch!

[roadnsky]

Interesting. The cap doesn't come pre-drilled, eh?

BS-
To add to Shawn's comments, the only "Pre-Drilled" diverter cap MMI sells is with the entire Side Plate Assembly. (Product No. - OVWJ_09.1_362)
"This side plate is completely assembled and ready for installation. It includes a "T" fitting and diverter cap (already installed) and a side plate gasket."

MORGAN 34-
If you've NEVER looked into that side plate AND don't know when it was last cleaned, you should put that high on your to do list.
Have you done any Acid or Vinegar Flushes? High Pressure flush?
How is your temperature at cruising RPM?