Pre-war (up to 1942) 1941 Cadillac Flathead Temperature Issues and System Flush

[J. Russo]

Hello all,

This is quite lengthy, but worth a read if you are having engine temperature issues or are thinking of flushing your cooling system.

I would first like to thank all the folks that advised me through this. Special thanks to Harry Scott for holding my hand through this entire experience.
This document explains the steps I followed for engine water/coolant flushing and removal of engine deposits in the 346 cubic inch V8 Flathead Engine. It also explains the replacement of the engine head gaskets.

My 1941 Series 63 has a new radiator core, new heater core, all new hoses and had a 50/50 coolant mixture.

In early July I took my Cadillac for about a 30-mile drive on the highway, averaging 55-60 MPH. I noticed that my temperature gauge was increasing while I was driving. The temperature gauge needle moved closer to "Hot" as I continued to drive. When I stopped the car, coolant was draining from the top of the radiator overflow tube.

I was informed that the average engine temperature should be between 180 and 190 degrees. I purchased a laser thermometer and found that my temperature readings were between 215 and 230 degrees depending on which area of the engine I checked. The bottom of the heads read in the 215 degree range while the upper part of the heads were in the 230 degree range.

In researching the CLC Forum, I learned that I was using the wrong radiator cap. I was using a 7 lb. pressure cap and the spec calls for a 9 lb. cap. I purchased and installed the 9 lb. pressure cap, but the engine temperature showed no improvement.

System Flush:
Harry recommended that I flush the system with a power washer as deposits accumulate over the years that result in engine hot spots. I used my gasoline powered power washer with a 0-degree angle adapter. I also did some research on the CLC forum and found a Cadillac Serviceman article dated September 1947 that detailed the recommended cleaning procedure. The article explains which bolts to be removed for the procedure, and requires that the water pump also be removed.

I first drained the entire system, removed all hoses, flushed the radiator with a garden hose and removed the drains from the bottom of the block. Once all water was drained from the block, I reinstalled the drains.

Removing the bolts was the most unnerving part of the procedure as I knew if I snap a bolt, I would have bigger issues. Harry gave me a great recommendation on bolt removal, recommending I use an air impact wrench, using short bursts until the bolt loosens.

Following the 1947 Serviceman instructions, I power washed the left side of the engine first. As I was power washing the right side, there was a lot of sludge being flushed out through the water pump opening. I also noticed water spraying out from the bottom rear of the right engine head. This could have been because of the loosened bolts, but as a precaution I decided to take this process 1 step further by removing the heads and replacing the head gaskets. I had to remove 21 bolts from each head. This is also where a great deal of patience is needed. I had many stubborn bolts that would not loosen. I tried the short bursts, first in reverse and then very short bursts in forward. I also tapped the bolt heads with a hammer. I sprayed penetrating oil, but I am not sure if that had an effect as the heads were painted and the threads were deep in the block under the head. I finally had to simply walk away for several hours or even until the next day before trying some of the bolts again. I was able to eventually remove all 42 bolts without incident. I examined each bolt for thread wear and replaced those that needed replaced with bolts purchased from Brad Ipsen.

With the heads removed, I taped over the valves and cylinders to protect them from water. I then was able to power wash the inside of the engine more thoroughly.  I also power washed each head, flushing out all debris.

The drains were removed on each side of the engine to release all water.
A rod with a magnet on the end was used to attract any leftover rust that settled at the bottom of the engine. I rinsed and drained each side of the block multiple times.
To gauge just how well the engine was cleaned, I measured the inside of the block from the inside bottom to the top of the block. Measurements were taken along the entire length of the block on both sides. The measurement should be about 8 inches if there is no obstruction. The right side of the block measured 8 inches the entire length. I did have a couple spots in the front of the left side that measured 7.5 inches. This simply means there are deposits too stubborn to remove.

Head/Block Cleaning and Prep:
I power washed the underside of each head. The gasket area of the head and the engine block were cleaned with a thin putty knife, brake cleaner, a razor blade and a scuff pad to insure good gasket adhesion. The underside of each head was also cleaned to remove carbon deposits. All bolt holes and passages were cleaned with different size wire cup brushes attached to a drill to remove carbon deposits and corrosion. Each head was soaked for about 24 hours in Evaporust to remove rust from inside and outside the heads. The heads were then rinsed with water, dried and re-painted Lasalle Green. A metal straight edge was used to check for gaps under each head and the top of the block. I measured many different angles to ensure there were no gaps.  Gaps could require the head to be milled.
The pistons had a lot of carbon deposits on them. The top of the pistons and valves were cleaned with brake cleaner and a scuff pad.

A 7/16-14 tap and die were used to clean all bolt and bolt hole threads before re-installing the heads with the new head gaskets.

Re-Assembly:
Gaskets needed before reassembly include water pump, water necks(2) and heads(2).
Permatex #2 was used for water pump and water neck gaskets as well as bolt threads.
Permatex High Tack spray or Copper Coat was recommended for the head gaskets. I used Permatex. Each head gasket should be sprayed on both sides.

I also coated the pistons and cylinders with oil before assembly, making sure there was no oil on the gasket area.

To help with head gasket placement, cut the heads of at least 4 bolts if you have extras, spread them out on each end of the block and screw them part way into the block. Do not screw them in too deep or you may not be able to grab them once you put the head in place.

Place the head gasket on the block over the headless bolts and then place the head over the gasket. There are photos provided related to the tightening sequence of the bolts. Partially tighten a couple of the permanent bolts before removing the headless bolts. I also installed the water neck with their gasket based on the tightening sequence.

Note: Pay close attention to the bolt heads. The water neck bolts have a special head and are not to be used anywhere else on the head. These bolts also cannot be substituted with other head bolts as they are different lengths and engine damage could result.

Use a torque wrench to follow the bolt tightening sequence in the photos for each side of the engine. The torque specification for head bolts is 70-75 ft lbs. The method I used was to first tighten all 21 bolts on each head at 50 ft. lbs., 21 bolts at 60, 21 bolts at 70. I did not tighten to 75 ft. lbs.
I installed the water pump with the new gasket, connected all hoses and filled the system with RO purified water and an anti-corrosion product called NO-Rosion.

Spark glug gap: .030
RPMs at idle: 380-400.
Dwell: 26 degrees.
Timing at 5 degrees BTDC

I ran the engine to full temperature, checked for leaks, turned off and let the engine cool until it was just warm. I then re-tightened every bolt one last time in the same sequence at 70 ft. lbs.

I drove the car for 29 miles averaging 35-40 MPH for 12 miles and 55-60 MPH for 17 miles. I noticed a difference in the temperature gauge in that it did not rise as high as it did before I began the cleaning process. When I returned home and with the car still running, I immediately took engine temperatures of multiple positions on the heads and the radiator.

The bottom(front/middle/back) of the heads read between 185-190 degrees. The top of the heads(front/middle/back) read between 196-203 degrees. These results were a 25-30 degree improvement compared to the temperature readings before I started the cleaning process. In addition, water was no longer draining from the overflow tube at the top of the radiator.

This process was a lot of work, but well worth it for me once completed.

If you are thinking of flushing and cleaning your cooling system due to temperature issues, be sure and check a few things first. Make sure your radiator, water pump and radiator cap are in good working order. Check your engine settings including idle speed and timing. If the timing is correct, you can try to advance it a little to see if the temperature improves.

[J. Russo]

Final Temperature Results:

[jagbuxx #12944]

Thank you for posting your process. It is something I will refer to if I ever need to do this for my '41.

[toybox]

Hi John , I did the same thing to our 46 when it was out of the car. The engine was a nice rebuild but I was concerned about the water jackets as I could see crud without looking to hard. What I found was lots of casting sand and some iron deposits. I could not believe how much sand was in there, maybe 1 to 2 inches and it was stubborn . I used a steel rod to scrape and knock it loose and yes the pressure washer was a good final flush. Thanks for the article . It's good to hear somebody else has had similar experiences . There is a great article on Walt's Workbench about this also.  We have never had a over heating problem since doing this and adding dual exhausts. We drove at 70mph across the southern Wyoming desert in August with no heating issues other then the people in the car. Thanks again ,Tim