Correct running temperature for the 4 cylinder wet liner engine

[tim hunt]

I was on here recently bleating about my engine struggling to get hot enough in any but the hottest weather. Even with a functioning 91 deg C stat, no mechanical fan, no rad shroud and the bottom five inches of the rad blanked off with a piece of hardboard on a motorway run at 3,000 rpm in top on Sunday with an ambient of around 20 deg C my temperature gauge was at about 3/8 scale deflection only.

 

In response to a suggestion I removed the sender from the thermostat housing, extended the lead from the gauge and clamped a long earth lead to the sender body so I could immerse the sender in a kettle of water whilst keeping an eye on the gauge as the water was heated. I found that "normal", I. e. a mid point deflection corresponded to 92 deg C and a 3/8 deflection such as noted whilst running as above corresponded to 85 degs C.

 

According to vapour pressure tables my 7psi rad cap should raise the boiling point of pure water to about 111 degs C and of course the 50/50 anti-freeze/water mix I run will give an even higher B.P. so I have no concerns about boiling. My question is whether 92 degs C is more or less the target "normal" running temperature for our engines or is my gauge under-reading? In other words, with an actual coolant temperature of 92 degs C should the gauge be indicating on the hot side of normal? Alternatively, might the sender be causing the gauge to under-read?

 

Tim

[tim hunt]

Sorry, I should have said 3,000 rpm in o/d top of course.

 

Tim

[MikeF]

Normal running temp is 185F = 85C. Pressure cap does not determine running temp.

Mike

[North London Mike]

Tim

 

LNK runs 185F in normal conditions, middle gauge, no crank fan and the elec fan brings her back down in smart order.........

 

Bit of a lottery regarding how accurate your / our dials are though ??

[tim hunt]

Thanks to both Mikes. I appreciate that the pressure cap does not dictate running temperature, just raises the B.P. I know the earlier cars had gauges with actual temperature figures and I take it that 185 F (85 C) is with a vertical needle, i.e. mid point deflection. From my experiment this temperature corresponds to about 3/8 on my gauge so at half way(~92 C) I may be running a little hotter than most. I'm not bothered about that, I have silicone hoses and would rather be running on the hot side of normal than cold for efficiency. I might, however, just tweak the Kenlowe control so that the fan cuts in a tad earlier than at present.

 

Tim

[stuart]

Different senders will give different gauge readings. This subject has been done very frequently on the 6 section of the forum. 185 is average running temp.

Stuart.

[RogerH]

Hi Tim,

has the gauge always read like this?

Have you fiddled with anything that is connected to the gauge?

The 3/8th = 92' suggests the needle is out of position - can this be adjusted internally?

Have you tried a different sender? They come in various colour codes, I think the TR4A is red (or yellow or blue).

 

Roger

[Steve Priest]

It might be worth checking the instrument voltage regulator, especially if you still have one of the old bimetallic-strip jobbies. A while back I swapped mine for a IC replacement and both guages (temperature and fuel) now give more accurate and stable readings.

 

Steve

[Guest]

I'm not to familiar with the 4's layout, but often the volt regulator is the culprit - often combined with a fuel gauge reading wrong as well.

 

Menno

 

 

Edit: you beat me Steve! Ah well, great minds think alike ;-)

 

Menno

Edited September 24, 2014 by Menno van Rij 2

[tim hunt]

By jingo there are some knowledgeable types on here! No Roger, I haven't been tinkering and the gauge has always read this way, 3/8 is 85, half way is 92. at least I now know that 85 is a satisfactory running temperature and my car is not running cold. I have no reason to suspect the voltage stabiliser since although it is the original my fuel gauge has always given steady sensible readings that I can rely on and the temperature gauge is steady too.

 

Menno - a close neighbour of mine, Kirk Myers, and his brother have a Saab sonnet each, you may know of them if there is an owners' club for this rare car.

 

Tim

[Guest]

Despite the steady reading of the fuel gauge, I would suggest trying a new one. It's one of the easiest jobs and on of the cheapest. I used to run a Spitfire 1500 with a similar voltage regulator set up and I was always pretty happy with the gauge readings until: steady as rocks. Until I found out that a Spit's temp needle needs to go up and down similar to the thermostat opening and closing! I changed the v/reg and lo and behold: both needles started to move like they were supposed to do (Sadly the fuel gauge needle dropped faster than I'd hoped for...)

 

And, don't forget: those early 60s gauges weren't rocket science... (It makes you wonder how British Engineers were able to hold the Vulcan bomber up in the air back then...).

 

@ the Sonett: I own the car since 08 or so. But I haven't touched over a year or so. It's under a tarp in a heated shed. Engine is fine, g/box is fine, tub is fine (now) - all I have to do(...) is find someone willing to take care of the body - it had a harsh life outside and there's osmosis (polyester smallpox so to speak) on/in the skin. It can be restored, but it's a mayor job which is expensive and more costly than the car's value when restored...

There is a Dutch Saab Club - quite an active one, with quite a few registered Sonetts. Always a joy to look at. In fact, there's one for sale across the school where I work...

http://www.saab-apeldoorn.nl/occasions/saab/sonett/saab_sonett_sonett_1_7_v4-1145888.html

 

Menno