ZENITH CD175 TEMPERATURE COMPENSATORS HELPFUL INFO

Hey hey,

I was trying to figure why i had a somewhat rough idle after a freeway run (the temp dropped a bit due to airflow) on my 3.5 V8 with the twin CD175 Stromberg setup. I found my issue and it was the temp compensators. They were out of sync and one closed more than the other when the air temp dropped (as well as the overall temp of the engine).

After a relatively long call with Burlen in the UK i managed to find out that the Temperature Compensators were not all made the same. Their opening temps varied and you could distinguish them by their marking. They have a letter stamped on one of their ''legs''.

Firstly, both of them need to have the same marking in order to achieve the closest opening rate possible between them. Some deviation from their nominal setting is of course something that cannot be avoided.

So what I have found will be listed below and indicates the factory set opening temperature relative to the marking on the compensators ''leg''.

''T'' marking ----> 27 degress Celsius

''N'' marking ----> 30 degrees Celsius

''U'' marking ----> 35 degrees Celsius

The best overall engine performance was made possible by using a set of ''T'' marked compensators.

There is one version that opens up at 20 degrees Celsius and has a ''120K'' marking on it but that was not ever fitted to the Rover V8 Strombergs.

The temperature compensator covers must fully seal against their body and not allow any air in. A bit of play is unavoidable in some instances but a good seal should be the primary focus.

That sort of possible issue checking however should come last in line and steps such as ignition timing check, air flow balancing between the carbs (which can be affected by a mismatched or not in synch temp comp pair), fuel mixture, spark plugs etc. must first be eliminated as possible causes for a rough running / idling motor.

Hope this helps anybody confused on the temperature compensators which usually tend to be screwed totally in (shut off) in order to avoid such issues. However i did notice poorer engine performance with them shut off and the mixture leaned out more.

Very usefull bit of information, as I'm finally doing some work on mine something to check, sometimes she's sputtering a bit, and I just changed those which solved that particular issue most of the time.

hef19898 said:

Very usefull bit of information, as I'm finally doing some work on mine something to check, sometimes she's sputtering a bit, and I just changed those which solved that particular issue most of the time.

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Glad you found it useful and almost eliminated the sputtering issues. Be sure to check the timing too. Some types of Rover V8s were really retarded timing - wise.

Mine is an 11D prefix and the manual says it should be (with all the vacuum pipes connected) at 4 to 8 ATDC. Others are at TDC and some are at around 6 degrees BTDC.

Mine actually works best when setup at lets say around 4 ATDC. So within the manuals range. You can pick up pinging etc using more advanced timing and also the exhaust starts to slightly pop on overrun.

Timing is good (-ish). It was a longer story, started with the heat issue and loss of power under load and got worse after JLR installed the new camshaft. Took some tinckering, replacing all spark plugs, the ignition lines and adjusting timing. Last time I drove it, months ago, it sputtered only occassionally and only, me thinks, two cylinders. Hence I'll check the thermo switches and then maybe valve springs, after adjusting the ignition timing again.

hef19898 said:

Timing is good (-ish). It was a longer story, started with the heat issue and loss of power under load and got worse after JLR installed the new camshaft. Took some tinckering, replacing all spark plugs, the ignition lines and adjusting timing. Last time I drove it, months ago, it sputtered only occassionally and only, me thinks, two cylinders. Hence I'll check the thermo switches and then maybe valve springs, after adjusting the ignition timing again.

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I understand ! Glad you got it sorted with only a minor issue to tackle.

In case you need info from the workshop manual please let me know i can scan the pages in the relative section and send them over.

Let me know about the temp compensators. Also be aware sometimes they get stuck and never open or remain half open. Some lubricant of your choice and brake cleaner and they go back to working order again.

I'll let you now! I did replace the left hand one, yesterday I found a new one when doing some other stuff in the car, so I am not sure I did the right one back the day (or the other way round, don't remember).

I am lucky, the car came with both, an official parts catalogue and a workshop manual. Thank you very much for the offer anyways! Because without a proper workshop manual, well, you are kind of lost, aren't you?

hef19898 said:

I'll let you now! I did replace the left hand one, yesterday I found a new one when doing some other stuff in the car, so I am not sure I did the right one back the day (or the other way round, don't remember).

I am lucky, the car came with both, an official parts catalogue and a workshop manual. Thank you very much for the offer anyways! Because without a proper workshop manual, well, you are kind of lost, aren't you?

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I see. I have an NOS spare one marked with the letter ''T'' and some other ones in my parts boxes in case you may need anything.

Well for me at least, the Workshop Manual is a huge help, especially with the electrics. Its got the whole wiring diagram which helps immensely !

Oh the wiring... First, mine is a hack job from 80s and 90s (trailer, additional headlights, speedometer, ship horn that could be switched of for MOT, Jaguar XK transistor ignition...) and a horrible mess, one that miracuolusly works. Funny so, that I have a grand total of 4 wiring diagramms, three in the workshop manual by model year and one in the original (I suppose) owners manual. None is correct, color codes don't match the original wiring installed 100% on either one... At least so, it seems they geberally correct. And yes, very, very helpfull!

hef19898 said:

Oh the wiring... First, mine is a hack job from 80s and 90s (trailer, additional headlights, speedometer, ship horn that could be switched of for MOT, Jaguar XK transistor ignition...) and a horrible mess, one that miracuolusly works. Funny so, that I have a grand total of 4 wiring diagramms, three in the workshop manual by model year and one in the original (I suppose) owners manual. None is correct, color codes don't match the original wiring installed 100% on either one... At least so, it seems they geberally correct. And yes, very, very helpfull!

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So, turns out I jave two U type temp compensators now. She runs very nice so, idles just fine at 800 revs, no sputter and just smooth without any fine tuning of the carbs being done.