1931 90 Overheating

[jules greenway]

Hi Guys

We've been having some hot weather in the UK (at last!) with temperatures in the mid 80s
I had to do a 100 mile trip in the 90 and found that although the car ran fine the temperature gauge went up to the highest point and on arriving, and letting the motor cool down, it took half a gallon of water to fill the rad (same on the return journey)
Obviously with a non pressurised cooling system one expects a certain amount of loss as the water evaporates, but is this amount usual? Was this normal if living in one of the hotter States?
All comments gratefully received

Jules

[unimogjohn]

Jules, do you have a thermostat installed? If yes, have you tested it to make sure it is opening/closing correctly? Partially clogged radiator? Slipping fan belt? When hot observe water flow at the radiator cap filler. Can you see water rapidly moving? If not, you could have a weak water pump. Of course, there could also be scale inside the engine causing hot spots/clogging.

Water usage, if your radiator was full to the top when cold, then you would lose some water due to expansion. If yes, then the amount to fill is about right.

[trimacar]

First thing to check is the water pump. If it's sucking air, through a grease fitting or seal, then coolant will foam and go out overflow. I had this happen on my Pierce Arrow, sucking through the grease fitting, put in correct grease and problem went away.

[jules greenway]

The thermostat on the '31 operates the Radiator Shutters so no problem there
Engine Block has been cleared of sludge and Rad flushed through
Water Pump rebuilt and appears to be working OK
I realise expansion will lose some fluid but was surprised at the amount lost?

cheers

Jules

[unimogjohn]

Jules, If you cannot see any leaks, then I would do as David suggests. When the engine is hot, look for bubbles in the radiator to make sure that you do not have a head gasket leak.

[Mark Shaw]

Also check the bottom hose to make sure it does not collapse when the engine warms up.... This will cause cavitation in the pump, foaming, & loss of coolant; not to mention damage to the pump.

[Fred Rawling]

Have you tried the old hand on the radiator trick to see if there are cold spots.

I am betting on the radiator being pluged up.

These radiators can be rodded out. There may also be sludge in the bottom tank that is plugging things up.

[jules greenway]

Thanks guys, will check as you suggest and report back

regards

Jules

PS Ironic that in a previous thread I was asking about installing a heater!!!

[Bob Engle]

You can't rod out a honeycomb radiator!! A test for the radiator is to remove the bottom hose, plug the bottom opening and fill the radiator with water. remove the plug and time how long it takes for the radiator to drain. Over 2 seconds and you have a radiator problem. I cleaned my 32 Buick radiator by blocking the thermostat opening. Then I stood the radiator upside down over a 5 gallon plastic bucket. I put 3 gallons of 200 degree water and a can of radiator flush in the bucket. I used a hot tub pump to pump from the bucket into the bottom radiator hose connection. I let the system run for several hours in this back flush mode. After this treatment, the radiator emptied in less that 1 second. I found about 1/2 a cup of grit in the bottom of the bucket when I was done.

Be very careful with radiator shops flushing these old radiators. They apply too much pressure and damage these honeycomb cores. These old systems were not designed for pressure.

Are your shutters full open when engine is hot?? Is your engien timing correct? too advanced will run hot. A lean fuel mixture will also cause an engine to run hot.

Bob Engle

[jules greenway]

Hi Bob
I thought that was the case re rodding out!
The engine is timed as per the book and I think mixture is correct-certainly uses plenty of gas! I like your suggestion for checking the flow rate and cleaning out if it is slow
many thanks

Jules

[Janousek]

I just completely rebuilt my 31' 90 and it's running hot but getting better the looser it gets. I didn't have the rad recored as last year the car always ran cool. I bumped the compression up to 6.6:1 with special pistons so I'm making more heat than last year. My car doesn't dump water though. I run it down an inch or two from the top. The two cars I have with non pressurized systems dump water until they are an inch or two from the top. Fill them up and they will dump and find their own level. I'm running the factory 10 degree advance setting running at idle. This is what my manual says to run. If I take an infrared gun on my top hose and compare the difference from the bottom hose it runs about 10 degrees difference. I've been told you need around 20 degrees difference. My new truck runs 30 degree difference but they are much better systems. One problem I have with my car is the exhaust manifold runs 600-750 degrees at the outlet. I feel this is a giant heat sink that maintains way to much heat in the head. I'm going to build a set of headers and ceramic coat them this winter to reduce underhood temps. Since I drive the car I will sacrifice some originality for drivability. The exhaust manifold is a rather restrictive design with each port adds heat from back to the front being the hottest. All these cubic inches are being compressed into a small tube and the heat is terrible. I'd like to hear what others think of this.

[jules greenway]

Hi Janousek
That's very interesting-I have also thought about trying to get rid of all the under hood heat but do not really want to go to the trouble of changing the exhaust manifold!
I agree with Bob that the problem is the flow through the radiator-I have some friends with vintage Bugattis which have the same problem. What happens is at cruising speeds the water pump is pushing the coolant up to the radiator header tank faster than it flows down through the rad, so it just empties out via the overflow tube-hence we can end up a gallon short after a 50 mile run!
I am going to do a flow check on the rad as Bob suggested (although I can't do it immediately) and will report back
regards
Jules

[Janousek]

I just reset my timing from 20 degrees total timing to 30 degrees and it runs a little cooler. I can't see how a radiator could dump it's entire load in 2 seconds. Are you sure that the 2 seconds is correct. Another thing to try is restricting your waterflow with an obstruction in your upper hose. This will slow your waterpump down and allow the radiator to do a better job. Most cars that have thermostats run all the coolant through an opening the size of your thumb. Our cars don't have that restriction which might not allow the radiator to do it's job. Another thing to experiment with.