Mungler Posted June 12, 2018 Report Share Posted June 12, 2018 So, I've got a 1987 300 SL Merc that is like Trigger's broom; I love the car and never see myself getting rid of it and in the years I've had it I've gradually had every job done that needs doing. The last issue is this. On a very hot day the car behaves like it is being suffocated - it runs and goes but there is a serious lack of "go" and little desire for the car to go up and down through the auto box. By this, if I've had a blast down some dual carriageway and pull up to a roundabout, when I pull away from the roundabout the car is ultra sluggish and seems to want to stay in a high gear and torque it out. When the car is colder it's responsive and will go up and down through the gears no problem. It's not gearbox related - that's already been done. I relayed these symptoms to someone I know who has an old Jag XK and he says that his car suffers from exactly the same problem in that in high temperatures the car can't properly circulate or dissipate heat under the bonnet and the carbs just don't like breathing hot air and as a result the car performs like it is being suffocated. Do the mechanics on here have any ideas? If this is a "hot air" issue then my first thought is to bolt on a dirty great big Ken Lowe electric fan and to then see what happens next. I may be mad, but I recall that Rover did a limited edition SDI Vitesse V8 twin plenum which had a water vapour injection kit as an option and which was apparently to resolve this sort of issue. I'm not going down that route but I am keen to diagnose and understand what's going on. Any and all thoughts welcome. Ta very, Mung. Quote Link to comment Share on other sites More sharing options...
figgy Posted June 12, 2018 Report Share Posted June 12, 2018 Try a piece of duct direct from near the grill or windscreen to near the airbox inlet so your drawing cooler air from outside the engine bay. Quote Link to comment Share on other sites More sharing options...
AVB Posted June 12, 2018 Report Share Posted June 12, 2018 Could you try more free flow air filter? K&N for example? Quote Link to comment Share on other sites More sharing options...
ph5172 Posted June 12, 2018 Report Share Posted June 12, 2018 (edited) A guy in the office runs a senator and has the same problem , he wired a switch to the engine fan so he can turn it on independently, he said it seems to have done the trick Edited June 12, 2018 by ph5172 Quote Link to comment Share on other sites More sharing options...
Mungler Posted June 12, 2018 Author Report Share Posted June 12, 2018 6 hours ago, figgy said: Try a piece of duct direct from near the grill or windscreen to near the airbox inlet so your drawing cooler air from outside the engine bay. I'll take a shifty at that. Not a bad start. 6 hours ago, AVB said: Could you try more free flow air filter? K&N for example? There's a K&N filter on there now but its in the factory housing 5 hours ago, ph5172 said: A guy in the office runs a senator and has the same problem , he wired a switch to the engine fan so he can turn it on independently, he said it seems to have done the trick Electric fan it is Quote Link to comment Share on other sites More sharing options...
figgy Posted June 12, 2018 Report Share Posted June 12, 2018 (edited) You can buy bigger or double fans to fit the back of your radiator but that's going to cool the engine temp too. Your more after cooling the air going into the engine, inter-cooler retrofitted from another car would help. Your auto box may need better airflow to its cooler too or the cooler maybe blocked if its playing up in hot weather. Edited June 12, 2018 by figgy Quote Link to comment Share on other sites More sharing options...
Guest Posted June 12, 2018 Report Share Posted June 12, 2018 It could be the warm weather is causing the petrol to vapourise before it gets to the pistons .it has be now to happen with carburettor engines Quote Link to comment Share on other sites More sharing options...
Mungler Posted June 12, 2018 Author Report Share Posted June 12, 2018 The car is currently back in with a specialist exhaust place - they installed a new front to back stainless system a couple of weeks ago (and with an altered gooseneck on the exhaust pipe to try and push the fumes outside of the vortex of the car - it's the usual old car problem of drop a window and get gassed). However, when the car ran and got hot the engine note to the exhaust changed dramatically to unbearably loud and which is why it's gone back today. They have phoned because they don't understand why the exhaust stainless has gone a golden colour - they said that's what they'd expect from a car that been round the Nurnberg ring and full pelt. However, on the dash board engine temperature is as steady as ever and sits all the time at half way up the dial (which is what every Merc I have ever had does). Thanks for the replies so far, I am formulating a plan. Quote Link to comment Share on other sites More sharing options...
Dave-G Posted June 12, 2018 Report Share Posted June 12, 2018 7 hours ago, Mungler said: By this, if I've had a blast down some dual carriageway and pull up to a roundabout, when I pull away from the roundabout the car is ultra sluggish and seems to want to stay in a high gear and torque it out. When the car is colder it's responsive and will go up and down through the gears no problem. I'm thinking there may be a torque sensor issue when the motor is warm. If it won't change down under load its going to be sluggish as a slug thing and can only get hotter and more bothered. Quote Link to comment Share on other sites More sharing options...
Loki Posted June 12, 2018 Report Share Posted June 12, 2018 Hiya Maybe drill into M-Benz 'enthusiasts' sites such as - https://forums.mbclub.co.uk/, to see what other have found and dealt with how....... L Quote Link to comment Share on other sites More sharing options...
Saltings Posted June 13, 2018 Report Share Posted June 13, 2018 too old for an egr blanking plate has the car been like this from new if not check fuel pressure as pump may be failing if not carbs jets wear out may need re jetting/ rebuild check plugs after a run look for a white brown colour if black too rich if white too lean also older vehicles do not run well on modern petrol as too much ethanol up to 20 % blend which also affects hoses gaskets etc in the fuel system witch gum everything up fuel starvation Quote Link to comment Share on other sites More sharing options...
bruno22rf Posted June 13, 2018 Report Share Posted June 13, 2018 Sounds like a possible fuel issue - get it on a Dyno/rolling road and get it mapped. Quote Link to comment Share on other sites More sharing options...
Dunkield Posted June 13, 2018 Report Share Posted June 13, 2018 If it is like many older cars and bikes it could well will be a fuel issue, they ethanol **** they sell these days is nothing like what that engine was designed to run on. A friend of mine has this issue with a '74 Midget, apparently it's to do with the calorific value of modern petrol, you may find it runs hotter as well. Swapping the stock filter for a K&N will only make it run leaner, which if anything could make the issue worse. Cheapest/simplest thing even you could do is get a Colurtune in one of the plug holes and see what it looks like, but I would get it someone who knows their old Mercs and get some analysis done on it. Or ... see if you can find a garage that still sells 4*, take a deep breath and fill her up, I run my bike on it and it loves it Quote Link to comment Share on other sites More sharing options...
Pistol p Posted June 13, 2018 Report Share Posted June 13, 2018 A kenlowe fan set up will help. Quote Link to comment Share on other sites More sharing options...
Mungler Posted June 13, 2018 Author Report Share Posted June 13, 2018 That’s plan A right there. Thanks chaps - I’m going to cut and paste this thread and add it to my to do list when the car goes in next. Quote Link to comment Share on other sites More sharing options...
chrisv Posted June 13, 2018 Report Share Posted June 13, 2018 Munger, It seems to be a really common problem. They mention a solution at around 8 minutes in the clip below. l'm sure extra fans would also help with temperature control, but sticking my head under the bonnet of a 3.0 Capri with an extra fan earlier this week, the heat seemed to be concentrated into the engine bay. Quote Link to comment Share on other sites More sharing options...
bornfree Posted June 13, 2018 Report Share Posted June 13, 2018 On 12/06/2018 at 17:52, Mungler said: The car is currently back in with a specialist exhaust place - they installed a new front to back stainless system a couple of weeks ago (and with an altered gooseneck on the exhaust pipe to try and push the fumes outside of the vortex of the car - it's the usual old car problem of drop a window and get gassed). However, when the car ran and got hot the engine note to the exhaust changed dramatically to unbearably loud and which is why it's gone back today. They have phoned because they don't understand why the exhaust stainless has gone a golden colour - they said that's what they'd expect from a car that been round the Nurnberg ring and full pelt. However, on the dash board engine temperature is as steady as ever and sits all the time at half way up the dial (which is what every Merc I have ever had does). Thanks for the replies so far, I am formulating a plan. That sounds like its running lean. Be careful or you may melt a piston. Quote Link to comment Share on other sites More sharing options...
Mungler Posted June 14, 2018 Author Report Share Posted June 14, 2018 (edited) 16 hours ago, bornfree said: That sounds like its running lean. Be careful or you may melt a piston. The exhaust people have said that the fibreglass baffles were melted. They have replaced with ceramic but have said their view is it’s running too lean. Next question - the specialist garage I take this to for servicing is in Ipswich (an hour down the A12 from me). Will it be safe to take the car at a steady 50 mph and not to go over 3,000 rpm? PS having watched the video clip too, what’s a ‘cold air pack’ in English? The yanks love ‘em, mind you they have the hotter climate. thanks again all Edited June 14, 2018 by Mungler Quote Link to comment Share on other sites More sharing options...
CharlieT Posted June 14, 2018 Report Share Posted June 14, 2018 I had a similar problem in an Audi Quatro some years ago. After many trips and I mean many to the garage, it turned out to be the braided fuel pipes had become slightly porous and in hot weather the fuel evaporated in the pipe where it went over the engine causing fuel starvation. Changing the fuel pipes to non braided ones cured the problem. Quote Link to comment Share on other sites More sharing options...
bornfree Posted June 14, 2018 Report Share Posted June 14, 2018 6 hours ago, Mungler said: The exhaust people have said that the fibreglass baffles were melted. They have replaced with ceramic but have said their view is it’s running too lean. Next question - the specialist garage I take this to for servicing is in Ipswich (an hour down the A12 from me). Will it be safe to take the car at a steady 50 mph and not to go over 3,000 rpm? PS having watched the video clip too, what’s a ‘cold air pack’ in English? The yanks love ‘em, mind you they have the hotter climate. thanks again all Its risky because you don't know where its running lean. It could be lean at part throttle . Quote Link to comment Share on other sites More sharing options...
Vince Green Posted June 14, 2018 Report Share Posted June 14, 2018 On 12/06/2018 at 18:21, Loki said: Hiya Maybe drill into M-Benz 'enthusiasts' sites such as - https://forums.mbclub.co.uk/, to see what other have found and dealt with how....... L I have always found the MB Club forum very helpful Quote Link to comment Share on other sites More sharing options...
Dunkield Posted June 14, 2018 Report Share Posted June 14, 2018 8 hours ago, Mungler said: The exhaust people have said that the fibreglass baffles were melted. They have replaced with ceramic but have said their view is it’s running too lean. As I suspected, stick the standard air filter back in it to richen it back up, then get is setup with whichever one you plan to use. Quote Link to comment Share on other sites More sharing options...
rovercoupe Posted June 14, 2018 Report Share Posted June 14, 2018 As a test you could get a cheapo thermometer with external sensor and run it into the air box and that will tell you exactly what temp the air going in is, did this years ago on a car and when sat in traffic it gets pretty hot! think it cost me about £4 Quote Link to comment Share on other sites More sharing options...
Jaymo Posted June 15, 2018 Report Share Posted June 15, 2018 Also Is there a diverter flap in the air filter intake? Could be stuck in the winter hot air position? And whip the plugs out and check the colour- a grey/white would indicate too lean , you want a nice biscuit colour Quote Link to comment Share on other sites More sharing options...
Mungler Posted June 17, 2018 Author Report Share Posted June 17, 2018 All the indications are it’s running too lean. I took the K&N off, put a factory air filter back on and then gingerly drove it to Ipswich for some proper love from a man that can. Thanks for the help and advice, it’s genuinely appreciated. Quote Link to comment Share on other sites More sharing options...
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