B18 B overheating

[Salop Farmer]

I wondering if I’m being paranoid but my newly built engine always seems to run hot( not off the scale but hot). I have tried with a second gauge and same story. When I open the bonnet after a run everything seems a bit to warm to my liking! Let me start at the beginning, After a long slow restoration I decided to give my 1960 PV a bit more power. I acquired a B18D engine, skimmed the head to give 10:1 CR fitted a K cam with new lifters and finished off with KD needles in the carbs. The block was bored and honed to +0.020 oversize and fitted with German manufactured pistons supplied by Brookhouse. The bores were checked for size before assembly and found to be spot on. I did notice on assembly that the pistons seemed a very close fit in the bores on the thrust side. Never the less I continued and checked rotation after fitting all four pistons. I have to admit the engine was slightly harder to turn than previous ones I have rebuilt. But I have presumed it will free up after running in. Admittedly the B16 radiator I am forced to use can’t help with this issue but it is in excellent condition and from hearing others experiences adequate for the job. Any suggestions will be most welcome. Thanks

[142 Guy]

Have you checked the thermostat to confirm that it is opening at the correct temperature? Also, you have installed the correct thermostat with the bypass shut off valve at the bottom (I assume the B18D has this feature). Other things that I can think of are:
- has your B16 rad been cleaned and flushed by a professional rad shop? Home flushing with a garden hose doesn't really do the trick on a seriously plugged radiator
- the bypass tube in the thermostat housing got moved and the little flap on the bottom of the thermostat is not closing it off when hot
- the water distribution pipe in the head has come loose / rotated / corroded and disappeared. If the water distribution pipe gets 'bunged' flow to the back of the head is impaired and that is where the dash temperature sensor is located.

I am assuming you don't have a coolant expansion tank. Purchase or borrow a flexible temperature probe. Take the rad cap off and run the engine at idle with the probe shoved down in the rad. On my B20E if I pull the rad fill cap off the is right above the top rad hose to the rad. If I shove a temperature probe down there I measure the coolant temperature just as it is exiting from the engine and I can watch the temperature go up and down as the thermostat closes and opens. This will also confirm if the thermostat is operating at the correct set point.

If the rad has not been cleaned in a caustic bath I would start with a flush and clean. The rad on my B20E looked just fine and pressure tested OK. However, after chronic running hot in hot weather I took my hand and ran it along the front of the rad fins. On the lower 1/3 of the radiator as you ran your hands horizontally across the fins (it is a horizontal cross flow) you could feel a drastic temperature drop mid way across the rad. The lower third of the rad was completely plugged. A trip to the rad shop fixed that up just fine.

[Ron Kwas]

SF; Engines do have more friction during break-in, but this should be (is) well within the cooling capacity of the Cooling Sys, and given its proper function would not be visible as a higher than normal CS temp...but...read on...

To add to the good info 142guy has given, and if you believe the B16 Rad might not have enough cooling capacity (and we know the B18 equipped cars did get a larger Rad, so that tells me they needed more BTU shedding capacity with the bigger engine!), I'd check the how much it drops the coolant temp between coming in from the engine and leaving to go back to the engine...(just estimating) it should easily be over 20 Degrees...but if it is any less then that, it suggests that Rad is not able to shed all the BTUs and temp will continue to climb...I do agree with 142guy, this is likely a CS issue...

Good Hunting, and please let us know what you find!

142guy; I've somewhat changed my thoughts on the CS Exp Tank...all it really buys you is the ability to do a quick visual level check since it's a translucent container...which is certainly nice, don't get me wrong, but function of the CS is no better really! Before the CS with ETs, heated coolant expanded into the airspace in the top of Rad (fill levels were lower to accommodate this!) ...once ETs were added, Coolant now expands into the airspace in the ET, and there is Auto-burping to keep the CS optimally filled (see: https://www.sw-em.com/Cooling_System..._with_Exp_Tank ), but again, I can see no significant performance improvement (Rad still has the same area, maybe fractionally larger, and coolant volume may be a bit more, which can't hurt)... Pressure is regulated by the Pressure Cap in both cases...

Coolant Distribution Tube is (essentially) pear-shaped in cross-section (see: https://www.sw-em.com/Coolant_Distri...Pipe_Notes.htm ) ...I always hear suspicions of it coming out of place but question how given its design, this might be possible, and I question if it has ever occurred for anyone...more likely IMO is sclerosis/calcification of the apertures (when note using approved coolant mixtures) causing reduced coolant delivery to the combustion chambers, and this has been observed...that's why inspecting the Tube during headwork is always good practice.

[142 Guy]

Ron:

I offer no opinion as to whether the closed system with expansion tank does a better job of cooling than the older design. My comment merely reflected the fact that my B20E has an expansion tank and as a result I was using the fill cap on the rad rather than the pressure cap on the tank for the temperature measurements.

I think the merits of the external expansion tank may depend on the relative free space in a sealed rad versus the expansion tank. I do remember the early seventies and on a hot day it was really common to see 'big ol' American V8s which were not equipped with expansion tanks burping coolant in a parking lot after having been parked 'hot'. Of course, I also remember a thread on Swedespeed where I asked a 140 owner whether he was continuously loosing coolant and he said 'yes he was'. In his engine photos his expansion tank was conspicuously filled to the brim which rather eliminated the expansion tank function. All of my cars have had expansion tank systems and none of them have ever burped when hot; however, I do respect the cold fill line on the tank. More is not always better.

Somewhere I thought I had seen a picture of a coolant distribution tube that had come seriously loose allowing it to back out of the mounting and move around. If it is not flopping around then that keyway on the tube should keep it positioned if the swedge has not failed.

[Salop Farmer]

Thank you for the replies, my first check will be with a temp.probe and find out if the rad is managing to do its job and drop the water temp. by 20deg. When I returned from a 20 mile run yesterday ( outside temp. 25 deg) the gauge in the car was just in the hot zone. The rad cap could be removed without any problem and I could put my hand anywhere on the honeycomb and detect an even temperature. Never the less from experience all seemed very warm under that hood. I could touch the rocker cover but not keep my hand on it.
During rebuild the waterways everywhere were thoroughly cleaned but I was unaware of the distribution tube fitted in the head so this was not inspected. The rad itself was inspected through the rad cap aperture, the vertical tubes seemed like new and flushing backed up this. New pump, thermostat and hoses were used and the heater system stripped and flushed.
Once stationary straight after my run and with engine turned off the gauge quickly climbs well into the hot zone.

[Rustinmotion]

I believe 10 degree F delta from top hose to bottom is the sign the radiator is working
Take out the thermostat and run it like that if your getting 10 degree delta and removing the thermostat does nothing then check water temp in radiator and compare with another B18
Or pull the sender unit and check what temp it’s actually reading by putting it into a cup of boiling water with a thermometer in it what’s middle of the gauge and what’s hot on the gauge

[Derek UK]

It's normal for the temp gauge to go into the hot after switching off, especially if you have just come back from a run. Heat soak raises the coolant temp in the block which is now not circulating. Actual temp you are seeing is specifically that of the coolant at the back of the head.
The rads maybe different but both the PV and the Amazon list as both being of 8.5l capacity. Some B20.s have a spacer between the fan and the pully. If you have room for one it could put the fan closer to the rad. That would be useful. The asymmetrical 5 blade plastic fan is supposed to be a bit more efficient and also quieter.
Personally I would consider fitting an electric fan in front of the rad. One large one or perhaps 2 smaller ones as it is a tall rad.

[142 Guy]

Originally Posted by Salop Farmer

When I returned from a 20 mile run yesterday ( outside temp. 25 deg) the gauge in the car was just in the hot zone. The rad cap could be removed without any problem and I could put my hand anywhere on the honeycomb and detect an even temperature. Never the less from experience all seemed very warm under that hood. I could touch the rocker cover but not keep my hand on it.

If "removed the rad cap without any problem" means that the coolant did not flash boil and vent then the coolant temperature was below 100 C which means that the temperature would appear to be in the OK zone. Remember that the head metal temperature will be higher than the coolant temperature (likely > 100C). The rocker cover temperature may not rise to the same temperature as the coolant passages in the head; but, I expect that uncomfortably hot to the touch would be pretty normal.

On my B20E I have two temperature sensors. The typical gauge sensor at the back of the head and the sensor at the front of the head for the D jet which sticks into the thermostat housing. With my digital ECU refit I can attach my laptop and data log the temperature measurements by the D jet sensor. My dash temperature gauge is a an electronic gauge with none of the typical measurement response damping that OEM gauges are usually equipped with. When idling, the gauge temperature sensor always reads hotter than the thermostat (D jet sensor) temperature. If I am out driving on a hot day and come to a stop for a long traffic light, I can watch the dash gauge temperature climb as the engine idles and it is quite common for there to be a spread of greater than 10 C between the front and the back of the head with the back of head temperature easily exceeding 100C. If I look at the logs of the front temperature it is typically around 90 - 94 C ( 92 C is the switch-on temperature for my fan) and I can watch the temperature rise and fall if the fan cycles. Once the light changes and I put the engine into gear the the dash gauge temperature drops and after 1-2 minutes will be within 2 C of the front of head temperature. This particular problem is purely a head temperature gradient / coolant flow problem, not a radiator capacity problem because I can also drop the gauge temperature by pressing the gas pedal to keep the revs around 2000 RPM which increases coolant flow to the back of the head.

My diagnosis from the other side of the Atlantic and never having seen your car is as follows;
- the acid test is that if your coolant is not boiling and venting through the pressure cap, you likely don't have an overheating issues under your present driving conditions,
- your temperature gauge might have some accuracy or at least calibration issues. I would be inclined to do the sensor in a pot of boiling water to at least get a sense of where 100C is. If you are out driving around and the temperature appears to be staying below 100C then you are probably good. It would be normal for the coolant to spike to 100C at idle or as noted, just after you shut the engine off (my previous comments about temperature rise and American V8s burping coolant in the parking lot).

I would not rush out and purchase an electric fan. Does your current rad have a fan shroud on it? If not, fabricating or retrofitting a fan shroud can improve air flow across the full surface of the radiator core which improves heat transfer at idle / low speed. Once you are above about 40km air flow due to vehicle movement becomes dominant. The fan is only there for idle / low speed driving conditions. Even on very hot days my electric fan generally shuts off at highway speeds. This presumes that there is nothing in the front grill that is impeding airflow to the radiator.

As a final thought, if the dash gauge going into the red bothers you there is a bit of a dodge. If your heater circuit is similar to the B20 (flow out the back of the head and back to engine at the water pump) with some hose and fittings you can fabricate a summer heater by-pass circuit. This allows for flow out the back of the head with a by-pass around the heater so you don't cook yourself. The increased coolant flow through the head will drop the back of head temperature. This doesn't increase overall cooling capacity, it just changes the coolant flow through the head. On Ron K's website there are links to people who have permanently modified their water distribution pipes increasing flow to the back cylinders which supposedly has a similar effect. I can't comment on the effectiveness of those modifications.

If it turns out that you are venting coolant or that your temperature gauge suggests that you are running consistently at 100C or above, then this might require some re thinking.

[Salop Farmer]

Thank you again 142Guy for a helpful comprehensive reply. We are experiencing quite hot weather over here in Uk around 24 - 26 degrees so this may well be adversely effecting temperature readings in my engine compartment just now. As you can imagine I am reluctant to drive far with what could be an overheating issue. I will take on board your suggestions and report back in due course. My car does have the 5 bladed plastic fan which can only be for the better.