I’m not familiar with the header tank but I seem to recall on another thread about the internals of the tank being somewhat odd with a tube going from one side to the other, or is that the S111 V12?
Could that have any bearing on the problem?
Sounds like he wasn’t getting vacuum to the capsule which will certainly make it run hot at cruise…I would fix that first.
Thanks Robin. Series one header tanks have an internal tube directing incoming coolant across the otter switch capsule. This replacement compared identically with the original that it replaced.
Robertshaw thermostat is NOT correct, nor is it really “sleeved”. It doesn’t control the bypass passage. That said, it should work well enough, as long as travel is sufficient. Since your radiator is clean and water is flowing, it’s the logical problem.
What’s bizarre? You have ported vacuum. No vacuum until you’re off idle.
He is getting vacuum above idle, but only through the mounting screw hole of the vacuum fitting(nipple)…NOT thru the actual nipple itself…bizarre.
Thanks Michael. I should have said a “modified” Robertshaw thermostat with the added 49mm second sleeve. Vacuum at carb takeoff now understood. If cover taken off, vacuum simply comes out of empty screwhole usually plugged. Vacuum correctly coming out of takeoff. As far as advance, the Mallory dual point vacuum/mechanical advance distributor is showing 9 degrees BTDC at idle and 27 degrees BTDC at 3000 RPM, as it has since I built the motor 15k miles/15 years ago, during which temperature was never a problem.
You don’t say if it overheats or not.
Has it ever overheated? Not shown higher than you like on the gauge, or puked a bit of coolant - I mean has it ever boiled? Since you have a clean rad and strong fan I assume the answer is no.
What’s with the ten pound cap on an ‘overflow tank’? Are you ratcheting down your coolant level somehow with an incorrecf cap sequence? You should have a twin-seal pressure cap on the header tank, nowhere else (and not ten psi on a 3.8). The header overflow goes to atmosphere or if you like to an open coolant recovery tank, from where it returns to the header on cooling if the hose end draws from the low part.
You should have no flow out of the header neck once you’ve had a ‘hot’ spell’.
Check if the distributor advance stuck retarded. This can cause that.
IIRC, one of my HD6 spare carbs has a plate w/vacuum nipple screwed to the flat on top of the carb throat, just forward of the throttle plate. There is a hole drilled down to the butterfly plate’s interface with the carb’s bore, but I seem to remember that the nipple is not directly above this passage, it is offset and uses a gasket to channel the vacuum over to the nipple’s base. If this is the case, and that gasket is compromised in some way, this could explain the lack of vacuum at the nipple.
Just reread your earlier post it looks like you have removed the plate and are getting vacuum at the wrong hole.
What temperature rating is your thermostat. Mine are both (3.4 liter xk150, 4.2 liter S1 type) 85C if memory serves. Temp gauges usually above that on both cars unless really COLD weather. I live in Kansas. Nothing wrong with running at 90C. 70ish seems too cold
27 degrees at high idle (3000 RPM, car in garage or driveway)? Your vacuum advance is not kicking in…should be closer to 40. 27 degrees is appropriate going down the road at full throttle, which would be the mechanical ONLY spec, but not nearly enough at cruise.
As an example, my 390 Ford runs with 36 degrees total mechanical advance, all in by 2800 RPM, but the vacuum advance adds another 12 at light load (high idle and steady cruise), bringing the total to 48. Yes, different engine, but same principle.
I thought this also too high.
I thought stock 3.8’s had very low pressure caps, but… I thought this was due to the type of original thermostat used. Since your thermostat is modified in some way, this may not apply.
The only suspect number is total advance, so you may as well fix that. But if you’re sure that it’s been like this all along, it’s not the problem. The radiator caps are not the problem. Check the fan again for proper direction of spin. When the engine is running hot, check the temperature at the upper and lower hose with your IR gun. If you’re not getting more than 10F drop, then suspect the radiator.
Great feedback folks, thanks! Answers;
- Never overheated and or boiled over. Highest witnessed of late is 105c/221f after puttering around after spirited run in 60 degree weather. Took forever to come back down.
- Used 10 lb cap due to system integrity, 4 seemed inadequate. Thermostat okay with 10.
- Bill Terry of Terry’s Jaguar (racing) advised that 27-29 degrees at 3000 rpm was good given my compression and 270 duration 380 lift camshaft profile. It has been set and run beautifully at 27 degrees at 3000, 32 at 3200 for 15 years without cooling issues.
- Fan is pulling properly.
- Temp drop is minimum of 10-15 F between upper and lower hoses. Once again, inside of radiator is spotless.
Unless there’s any more suggestions, I’m tempted to pull the water pump to see if Lee’s experience with impeller being loose on shaft is at issue. I have no other idea as to measure velocity of pump.
I agree 10 psi cap rating is not the problem but the use of an overflow tank with a higher rating than a non-return cap on the header could be. I’m just wondering what kind of ‘overflow tank’ is fitted and why one would bother with a redundant lower pressure cap on the header tank. There’s no point running, say, 7 psi on the original location and then plumbing 10 psi downstream in a closed system - which thereby becomes a 10 psi system…But most importantly, IIRC the OP has not said if his car has ever overheated, has never described the plumbing of his system, and never said what happens if he just leaves it idling for an extended period beyond when the fan cycles on and off - assuming it does so indefinitely as it should - meaning there is no serious problem.
Too many critical variables unaccounted for. …
Chuck, how did you make this determination?
Tom
Michael, there is no overflow tank, just the header with a 10 lb cap. The radiator has a 22 lb non return cap on it. Otherwise, it is a stock cooling system design for a 3.8 November '61 build as far as the plumbing goes. Changes include the discussed thermostat, new header tank, one of your 10 blade fans, a Howe aluminum radiator. No, the car has not overheated, . It simply, abruptly appeared to lose a considerable amount of efficiency. Example, in 60 degree weather after a run, with gauge temp (confirmed by IR reading at manifold) at 90, fan running, it will barely work it’s way back down to 80’s if at all. The fan will not cycle off at all, staying above the shut off temperature. The point being is that it used to easily cycle off quickly on a 60 degree day. I simply want to correct before 90’s arrive (soon).
Tommd55, having the header cap off, revving the motor, watching the cross flow in the tank increase.
Peter was asking about an overflow tank. I assume you’re using a converted Howe radiator, originally intended for a Chevy application. What is your idle speed? Has it changed at all?
It could be the water pump, I hesitated to suggest that because it’s a ton of work to check and not a common failure mode.
You can see where the confusion crept in…
Now there’s an added wrinkle…
[quote=“Chuck_Stone3, post:37, topic:389237”]
The radiator has a 22 lb non return cap on it." [/quote]
Gentlemen, sincerest apologies for the confusion on the tank. Idle speed set to 900 due to lumpy cams.
So, you’ve seen water pump failure without any visibly external cues?