Spike's SEC Teething troubles... Making Some Different Progress.

[spike60]

As some of you may have seen I recently acquired a 1985 Mercedes SEC 500 which while it had a fairly new MOT was unused for 17 years. I've put a couple of cars back on the road after a long lay off so I expected niggles to come out of the woodwork when it got used and it hasn't disappointed.

 

Today's issue is temperature, on start from cold it warms normally to about 85c, then quickly goes to 95-105c and then drops like a stone down to 85c in about 8 seconds. Once it has done this it behaves normally on A roads, town or idling until it's parked and allowed to cool when the cycle starts again. 

 

It has a new MB thermostat which made no difference, the belts are all fit for purpose, the radiator passes coolant and air freely and the air flow to it unimpeded.

A temp gun confirmed the dash is reading right, with it hot idling 90c at thermostat housing, 74c top hose, 85c rad top, 34c bottom hose.

 

Is a 40c temp drop across a radiator normal? Are the figures pointing to a coolant flow issue? I'm looking at replacing the water pump next because can't imagine what else it could be. The usual suspects for hot running, head gasket etc stay hot, not just on warm up.

 

Any ideas and thoughts mucho appreciated!

[cort16]

Is the electric fan thermo switch kicking the fans in at the right time? Presuming it's electric and not a clutch but the same could apply

[spike60]

It has a viscous belt driven fan which seems ok and a back up/air con electric one which doesn't. I think the electric one is set to about 110c so this shouldn't be a factor, the car shouldn't get that hot anyway. Once warmed through the car will idle at a steady 85/90 on just the belt driven fan, this drops the rad temp by 40c.

 

When I went to see the car it seemed to have plain water in which isn't great but ran well on test, the warm up antics only seem to have started on my watch.

[cort16]

the fan clutch might not be engaging on initial cycle then it's kicking in and working as normal up to a certain temperature. You could do the fun activity of sticking on a set of welding gloves and checking the clutch has engaged by trying to stop it.

[spike60]

No thanks, it's metal bladed as I noticed when I put the temp gun in the firing line! TBH I would imagine it would do just fine without a fan as long as moving, I had a fanless Volvo 144 for 4 years, I only remembered every time the brake lights came on on the A1.......

I don't think it's airflow related as isn't affected by speed but i'm open to suggestions.

[spike60]

I'll see if I can short the fan relay out to bring it in but i think it's a last resort fan, mebby useful in Las vegas , not so much Redcar. It's only momentarily peaking at 100c+ plus I don't feel it what a 35 year ols all aluminium engine needs. 

[spike60]

I finally got round to another go at the bugger and shorted the electric fan sensor to earth, it worked fine but made no difference to the temp.

I tried vacuum bleeding it from the small return on the thermostat housing but no joy, seemingly blocked, Hmm. It turned out to have a small ball bearing inside the fitting, presumably to act as a check valve when the pump is running. I took this out hoping it may be sticking but nope, exactly the same.

As a stop gap so I can actually use it I've ordered a 75c thermostat to replace the standard 84c, i don't expect it to cure it but hopefully it will bring down down the temp peak below 100c making it less likely to cook something.

[J-T]

Hope you get it sorted chap.

 

Please stick some more pics of it up as I thought it looked bloody spectacular!

[Dead_E23]

It doesn't sound like there's much wrong with it to me.  Is it doing anything bad as a result, or is it just that the guage looks a bit alarming?

[spike60]

It doesn't sound like there's much wrong with it to me.  Is it doing anything bad as a result, or is it just that the guage looks a bit alarming?

The gauge looks a bit alarming backed up by a temp gun,  the thermostat housing getting toward 110c until plunges down. 

[spike60]

Hope you get it sorted chap.

 

Please stick some more pics of it up as I thought it looked bloody spectacular!

Hopefully I will, I'm fairly persistent. I put the original thermostat back today and the fault has changed but still there so I think the problem may lay there somewhere.

Sorry, no new pics the only ones I have have been posted though someone else took some at Tesco's today! The pics flatter it, the paint is  bloomy and  could do with a good cut and polish but my priority has been getting it useable first.

[Strela]

I have the 3.8 engine and it does the same after starting from cold, although not over such a big range. It is perfectly normal for it to nudge momentarily over 90 then immediately drop back to a steady 80ish. Like yours, once it's warm the temp is very constant, only indicating a slight creep under particularly heavy load. And mine was rebuilt by a proper classic Merc specialist very recently.

[cort16]

How’s the heater during the initial hot run?

[spike60]

I have the 3.8 engine and it does the same after starting from cold, although not over such a big range. It is perfectly normal for it to nudge momentarily over 90 then immediately drop back to a steady 80ish. Like yours, once it's warm the temp is very constant, only indicating a slight creep under particularly heavy load. And mine was rebuilt by a proper classic Merc specialist very recently.

This seems to to something it developed since I picked it up, it was fine on the test drive and and 30 odd miles it made home.

I put the original thermostat back it and it now does its cycle twice as it did when it was fitted before I changed it, compared to once with the replacement stat which is about 5c hotter. 

My concern is the 100c+ it reaches momentarily  every time i use it, if I can get it 90c I'll shrug and let it go.

Some of the forums seem to have some elaborate bleeding methods, my next task I guess. 

[spike60]

How’s the heater during the initial hot run?

Seems fine though the climate control seems to lag making it hard be sure. Lack of heat doesn't seem to be a issue.

[Dead_E23]

That's why the cooling system is pressurised, so the coolant can go over 100C without boiling (or more precisely, why it's sealed and radiator caps have a spring in them so it doesn't explode).

[spike60]

I'd rather the 35 year old gaskets weren't heated to 105c then dropped 20-25c in a few seconds within 4 miles every time I use it. I don't suppose it it did it in 1985! 

[richardmorris]

My 320 e class had one similar period of wildly fluctuating temperatures. Driving along the m6/42 in freezing conditions the gauge shot up to 110 before instantly dropping to 70 ish and then climbing back to 88ish normal. And repeating- it made me very nervous for a while, but it has never ever done this again and I had a new thermostat fitted later on that year as I assumed it was the problem.

 

Although given the speed of the fluctuations it could well have been an electrical problem with the gauge.

 

Edit, before the new thermostat a couple of years ago, the temp would be at about 80 on a run then instantly climb to well over 100 in traffic until the twin a/c fans cut in. After replacing the thermostat I tested the old one- it opened partially at about 50 and that was it, it opened early and never opened fully.

[spike60]

I'm pretty sure the dash is telling the truth, a temp gun confirms though actually reads about 5c higher than the dash. Old stat 2 cycles/ 80c on dash when settled, new stat 1 cycle/ 85c on dash. Any bets on the 75c stat currently winging it's way from Jarmany as I type?

It also works normally the first time I use the car after refitting the thermostat before reverting to it's old ways. 4 or 5 times now.....

[spike60]

About 2 weeks ago I fitted the 75c thermostat in place of the standard 84c and it initially went to 95c peak  before dropping a couple of times to and staying at 80c but in the last week it has been good as gold. I don't understand why a cooler stat should stop the cycles, I was just trying to lower the peak temperature but I'll take a win however it comes. . It now stays at 80c.

 

The other biggy was cutting out/not starting, the bugger stopped on the A19 halfway home on collection but then started fine after the AA dropped it off. The fuel pump relay had been resoldered inside but still wasn't great, I replaced it with the finest Chinese electronics for £17 inc p+p and all seemed well. 

 

Then a couple of weeks later no start again on the drive, the silent fuel pump  giving me the nod I was at least clutching at straws in right field. Again it started later without me doing anything, not helpful. I fitted a pattern pump and filter and did another 350 miles without problem. Then it did again. also on the drive, but this time it stayed broken. 

 

So last Sunday I systematically went through the pump wiring and found no connection from the relay to the pump. Undoing the fusebox I found some nice aftermarket barrel connectors and wiring, some of which went into the pump feed. 

I chopped the intruders out and rejoined the wiring as MB intended and the pump ran. 

 

So next job is to get rid of the redundant alarm/immobiliser and the mass of wiring it has and properly rejoin the pump wiring along with tracking it.  It pulls badly left and the track rods were both bent when I got it,  It would be shame if the 2001 Nankang M+S's wore out, especially as it feels like a rear isn't very round anymore.....

 

It's had a week on general work duty so it had a scub up this morning.

 

 

 

The pics flatter it a little, the paint is a bit patchworky and the horizontal stuff is  bloomy and swirly.

[HMC]

Good result on the stat. Maybe the Mb replacement one was a bit lazy just to lead you astray? Having said that I’ve bought loads of new Mb stats over the years and never had a dud, although each of the 4 v8 126 chassis cars I’ve owned came to me needing a new one due to over cooling issues.

 

Car looks amazing BTW!

[dome]

Good work on the troubleshooting.

I wonder if the dodgy fuel pump wiring is leftover from an old alarm/immobilizer install?

[spike60]

Good work on the troubleshooting.

I wonder if the dodgy fuel pump wiring is leftover from an old alarm/immobilizer install?

That's exactly what it is, though the wiring is neat enough that I think it's been professional but the unit it goes to is having having senior flashback moments. I need to find out what the other 8 wires go to before riving it all out. It also has some mystery wiring going through the bulkhead from the battery.

[J-T]

I really really really really really like that car. Everything about it gives me the horn. I is jealous. As you were.

[Jim Bell]

Imobilisors are the devil's plaything. Hope all the mystery wires come out easy man.

[spike60]

It seem to have proper loom, not a few Halfords wires put in on a Sunday morning before pub time.  Guess it wouldn't be much of an immobiliser if it was easy to remove.

[Schaefft]

What a color. Obviously I approve, its good to see another SEC receiving the attention it deserves. I tried calling the MB dealer yesterday to see if I maybe could actually get a decent price for a set of wipers and an ABS sensor from them. 81 quid for the former and 400 for the latter unfortunately didn't help my mistrust when it comes to dealer prices.

[Jim Bell]

What a color. Obviously I approve, its good to see another SEC receiving the attention it deserves. I tried calling the MB dealer yesterday to see if I maybe could actually get a decent price for a set of wipers and an ABS sensor from them. 81 quid for the former and 400 for the latter unfortunately didn't help my mistrust when it comes to dealer prices.

 

Id be careful with ABS sensors.  I think the lad at my local garage said that he tried four ABS sensors on an SL and the ONLY ONE that would keep the abs light off was one from the dealers.  Even though the part numbers matched and they looked to be from the same fucking manufacturer.

[Schaefft]

Well, I usually buy them from the OEM supplier, this time I had to settle with a used sensor that is said to work (it better does for 140 Euro). Seems to be a single year only part as well which adds to the fun.

[Jim Bell]

Well, I usually buy them from the OEM supplier, this time I had to settle with a used sensor that is said to work (it better does for 140 Euro). Seems to be a single year only part as well which adds to the fun.

I'm sure Richard K had similar issues with his if I recall correctly.

 

The curse of classic Benzes!