Hi all, 1930-'31 Ford coupe AV8 hot rod. '39 trans, banjo rear, closed driveline. 59AB bored .030, stock cam, two carb manifold with Holley 94's, Edelbrock heads. 150 psi compression in all cylinders. Runs great. My 59 AB runs very cool. When I first completed my build it was running only at 140 degrees and not running well, stumbling a lot, so I put the Volvo thermostats in it at 170 degrees. All was good. Engine ran much better settling in it about 160 degrees during the warmer months. However in colder weather like now the engine settles in at 150-160 degrees and does not run as well, stumbling a bit but not as terribly as when it was running at 140 degrees initially. The cooling system is obviously in very good condition, able to keep the flatty well below overheating even in very high outside temperatures. My question is, what exactly is the correct operating temperature for my flatty and should I go to a higher temperature thermostat as the engine seems to run better when it is at a higher operating temp. I'm thinking it should be running about 180 degrees. any suggestions? Thanks, Andy
That’s what I always thought. They ran hot. So around 180-190 degrees. But not forsure. Sent from my iPhone using H.A.M.B.
I drove my flathead powered sedan last weekend in 40 degree temps. It got up to about 140 degrees on the highway at 65 MPH. I bet we are the only people in the world wondering why our flatheads run so cool. (I actually know why mine runs cool)
I've heard the same as Boden, 180-190 degrees. I have the 6 cylinder H-Series in my 41. I am running a 180 degree thermostat and it runs very well.
During Your summer driving you’re obviously at a good setting with both your fuel flow and advance settings. 180 degrees is a perfect operating temperature. Running below operating temps is the hardest thing for any engine. I can’t really see you running during the winter much in your neck of the woods but if you do drive more than normal during the winter you could install some 180 thermostats. Are you running an automatic choke?
Just for curiosity sake, what dual intake are you running and you wouldn't happen to have the heat risers blocked off would you?
Mine runs very cool too. The last day I was out in 35° temperature, mine only got up to 140-150°. I have 180° thermostats in, which I'll get up to in warm weather. I have a very thick 3-1/2" radiator core cause I knew flatheads run hot
I just installed a fresh H&H flathead with aluminum heads, 160 degree thermostats, four core radiator and had to put paper on the front of the radiator to get it above 140 degrees. Better to have it run cool, less problems.
!80 - 190 is GR8. 180 stats in mine & it runs in that range in the summer. In the fall i may restrict air to the rad. to get it over 160.
Got one of those HF radar heat guns that shoots the red beam - because I just wasn't believing the gauge - nice to have one for a second opinion. The third flattie - stock 8BA - I went through for a 1950 club coupe ran soo cool - stock radiator and fan set up - cool enough I drove it to the swap meet to sell - it could sit and idle for 30 minutes or more and just be luke warm inside the radiator.
In one of the perennial "What Motor Oil Should I Use?" threads I thought I remember reading something about a certain minimum oil temperature being desirable, not only to boil off moisture and contaminates but for the multi-viscosity oil to actually reach the high number viscosity or somesuch. Oil temperature lags water by quite a bit, but running any engine "too cool" is not beneficial. Flatheads are different though.
Do like my dad used to do with his flathead's Take the fan off in the winter. It was the only way it would get warm enough to get heat out of the heater.
No heat risers in cold weather can cause some pretty bad drivability. The carbs need that added heat to help atomize the fuel in cold weather. I have heard that complaint more than once!
No, that's not accurate. Multi-viscosity oil does not increase in viscosity as it heats up, it just doesn't thin out as much as a straight grade would. All oils decrease in viscosity as they heat up, and increase in viscosity as they cool down. The rate at which they do it is called the Viscosity Index. The higher the VI, the less the viscosity changes with temp.
I've heard many times that it's hard on an engine to run cool, but I've never really grasped why that is. Is this about efficiency, where the engine runs less efficiently, and so burns more fuel per mile? That I can understand. Or is it about wear? What's going on with that? Thanks!
Right, I know that, but there was some claim along the lines that the oil won't "work right" (for lack of a better phrase) unless and until it reaches a certain minimum temperature, unrelated to boiling off contaminates. I was hoping you'd opine.
With my '36 coupe I run a pair of 190's in my 8cm Merc engine after switching from 180s. I have 25k trouble free miles on it over the past few years in all types of year round weather. Long and short distance trips too. Run those flatheads hot and consistent for best economy and a clean sludge free engine. A clean / new radiator and a boiled out block are the keys to consistent operating temps on these old flattys. This remedies 99% of all overheating problems and allows them to run nice and warm for miles and miles. A cruddy radiator and scaly block will plague you with over heating problems. That is where most novice car guys go wrong, cleanliness of the cooling system is crucial.
The low temperature would not necessarily be causing the motor to run poorly. Like sidevalvev8 says, you need the heat riser or some heat up to the manifold. I have two flatheads that run too cold but they run well. Nothing wrong with trying to 180 thermostats though. As a side note, I have had a problem keeping the thermostats in place. They flip up and then the water bypasses them.
expansion rates, and tolerances if the motor was designed to run a certain clearance at 180* and now your running 120* you just opened up your clearance by a decent margin , gm had a typical issue with piston noise on cold start in the later sbc, same deal, soon as piston got operating temp it was happy and quiet... colder it runs you would risk more blow by contamination of oil ...on a Flathead though i would be happy at 160* and change oil more frequently
[/QUOTE] Thanks for your comments. This question has been raised before, but left unanswered. Mine has run at 140 for as long as I have had it. Might be time to up the thermostats....
Thanks for your comments. This question has been raised before, but left unanswered. Mine has run at 140 for as long as I have had it. Might be time to up the thermostats....[/QUOTE] That’s just my take on it as a machinist and looking at things as a wearing mechanical thing my guess is there also some science behind the optimum operating temp area for fuel burn effectiveness ect
I slide a piece of smaller hose on the inside of the radiator hose. I think it is holding it in place.
I'm still in some kind of thermostat vortex zone with my 8BA. I have the 3rd set of stats in this engine, all some kind of name brand, all 180 degree. Driving around town, both sides of engine might get up to about 180. Head out on the road, goes down to 140 and stays there. I think my gauges are pretty close to accurate. Been thinking about spending more for those Robertshaw ones, but jesus, I got a whole box of 180 thermostats.
If your temp goes down on the highway,,,,at least you know your radiator is flowing well. Maybe too well. Tommy
When I built my flathead 20 years ago I was very concerned about overheating because everybody told me they overheat. I added two mechanical gauges (one in each head) and a electric gauge. Funny as they agreed with each other and she runs between 160 to 180 depending on ambient temp. I ended up pulling the two extra gauges to clean up the dash. Didn't need them anyway.
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