1991 300GD 6 cyl 603D30
I'm gradually becoming acquainted with my new baby and not having driven a non-turbo diesel before I have a few queries. The car has 168,000 kms- genuine.
Firstly torque peak is at 2900rpm and max output at 4400rpm. Although the engine seems fine and isnt using oil, it feels heartless to take it to this higher rev level. I had thought-naively perhaps, that diesels were lower revving. But at 3000 to 3500rpm on highways it is plain slow. Its tickover and unstressed temp is 90, but the temperature creeps rapidly a few mm over the horizontal line whenever it is under load indicating 100+. Should this acute temperature sensitivity occur? Having done a 600mile run a few days ago, and needing to keep the pace up at around 4000rpm - hardly 120kph-72mph, it returned 23MPG av; and sat at 95+ degrees is this reasonable? I am running on new 205x16 Bridgestone Duellers (inflated to 44lbs) on steel rims. thanks Tombo
I can't speak about the temp but in regards to the RPM you will be running very high revs when on the highway as they aren't geared for speed - my old 300GDS would run at about 4500 RPM at 80mph if memory serves.
But being a Merc diesel it will happily do that all day - that is until you hit a hill.
Of course somebody here might correct me on the RPMs....
Is it auto?
My auto does 20mph/ 1000rpm so 4000rpm is 80 mph. Don't worry about reving it highly, I regularly take mine to 4500 when accellerating through the gears. You certainly need to do that to hit 60mph in less than 22 seconds.
Temp does seem a touch high, but the thermostat doesn't fully open until 95c. I have driven long distances at 100c on a warm day at 75-80.
23mpg is ok at that speed. If it uses no oil or water then it sounds spot on
Tombo,
I also have a 1991 300GD SWB LHD manual. I had it while living in the south of England for almost three years before I moved back to Spain in 2005. While in England, I had no temperature issues whatsoever and the G would run all day at some 85º whatever the weather, though, admitedly, it had very little use at motorway speeds.
In September 2005 and immediately after I moved back to Spain, I replaced the engine for a brand-new one. The old one had a hairline crack in the head and I was offered a factory-new engine at a fraction of its cost. As soon as i had the engine installed and though it was still farily cold, I noticed the symptoms you described as soon as I travelled fast on the hilly motorways in this part of the country.
You see, the standard thermostat opens when the engine is too hot. And the cores in the aluminium radiator are horizontal rather than vertical; this makes 16 years of use create a lot of deposits which cannot simply be flushed away when you replace the cooling fluid. I was advised that I had to replace the radiator and once I had to write a check decided to got for the full treatment. This included:
New BEHR aluminium radiator
New 85º thermostat
Smaller waterpump pulley so that a higher volume of cooling fluis is moved
New smaller engine belt to accomodate for the smaller pulley
Once all that was done, my G is able to climb motorway hills at full throttle, with 40º ambient temperature and aircon on, all day long and the water temp does not move from 85º
I am not suggesting that you might need any of these, given that climate in England has nothing to do with that of central Spain, but I would certainly monitor that temperature.
As for the engine speeds, a 300GD manual with 205R16s does exactly 4,000 revs at 120 Km/h (75 mph). The most effective solution to tackle this issue and add some clearance under your diffs for more safe and efefctive off-road driving is to replace the tyres with a set of 235/85R16s, This would increase the gearing by almost 10%.
Good luck.
Again thank you Jesus for your wisdom in these matters.
There is a cooler thermostat which was fitted to the later turbo diesels 350 and 300 24v. It can be swapped for the standard one, and I have done that. It opens at 80 and is fully open by 94.
60-70 mph will produce considerable fuel savings in the order of 27mpg on an open road and much less stress.
Sit back, relax, let the Mondeos fly past you and enjoy the trip.
Hi Tombo My 1991 LWB 300gd 603 diesel automatic is fitted with an aftermarket turbo and intercooler.it returns 26mpg motorway driving at 70mph /3500 rpm...(there are no records broken getting to seventy mph) I get 16/18mpg off motorway...the turbo has it own airfilter so the 603 standard air filter cartridge is not used...the clips on the housing are not capable of holding the increased boost pressure from the turbo so twelve 2mm screws and nuts are fitted around the flange.the exhaust is the original diesel 463 with a wide bore pipe inserted a the turbo end...In my opinion an inline single muffler with short tail pipe would allow the turbo to "breathe" properly and greatly increase the current performance at the low end of the torque range
Even when worked hard my 603 hardly touches 80 Celsius. I have fitted the turbo thermostat though and it has a new rad. (in prep. For a Morocco trip). The temp’s you describe just don’t sound right. I wouldn’t expect it to alter by more than 5 Celsius between easy and hard use. Certainly our 3 diesels operate in this region.
Re. performance, having only driven Tdi diesels to any great extent before this, it does have very un diesel like characteristics. As Roly says it’s no problem revving it to beyond 4000rpm and indeed seems to like rev’s sounding totally unstressed. Very unlike my Toyota (modern common rail technology) which sounds like a bag of spanners when revved beyond 3000rpm, which BTW achieves nothing in performance terms.
Very grateful to all comments recieved. New rad ordered from Behr. Will try it with new 85degree thermostat as 85 seems viable working temp if maintained and car is originally supplied with this rating. Crisis over tyres as 2 Bridgestones just bought and other pair nearly new, but logic understood- any takers out there? I will likely switch. What chance in finding 6J 16 alloys as I am driving without spats, and at what price. Incidentally does anyone know offhand the actual difference in weight between a standard early463- 6jx16 steel and alloy wheel? Thanks again Tombo
Very grateful to all comments recieved. New rad ordered from Behr. Will try it with new 85degree thermostat as 85 seems viable working temp if maintained and car is originally supplied with this rating. Crisis over tyres as 2 Bridgestones just bought and other pair nearly new, but logic understood- any takers out there? I will likely switch. What chance in finding 6J 16 alloys as I am driving without spats, and at what price. Incidentally does anyone know offhand the actual difference in weight between a standard early463- 6jx16 steel and alloy wheel? Thanks again Tombo
As in most cases with wheels that are not huge, the difference in weight is unimportant. It's the aesthetics what count!
I would definitely upgrade to the 6J16 alloys, since they should not be expensive (they are not as desirable as the 7x15 that people use with the flared wheelarches). I cannot say how much but I bought one once from Mark Vulture for 20 squid and a second one from a coleague in Madrid for 40 quid (this one including an almost new tyre). I guess your best bet to buy cheap would be German Ebay, even after shipping to the UK has been taken into consideration...
tombo wrote:Very grateful to all comments recieved. New rad ordered from Behr. Will try it with new 85degree thermostat as 85 seems viable working temp if maintained and car is originally supplied with this rating. Crisis over tyres as 2 Bridgestones just bought and other pair nearly new, but logic understood- any takers out there? I will likely switch. What chance in finding 6J 16 alloys as I am driving without spats, and at what price. Incidentally does anyone know offhand the actual difference in weight between a standard early463- 6jx16 steel and alloy wheel? Thanks again Tombo
As in most cases with wheels that are not huge, the difference in weight is unimportant. It's the aesthetics what count!
I would definitely upgrade to the 6J16 alloys, since they should not be expensive (they are not as desirable as the 7x15 that people use with the flared wheelarches). I cannot say how much but I bought one once from Mark Vulture for 20 squid and a second one from a coleague in Madrid for 40 quid (this one including an almost new tyre). I guess your best bet to buy cheap would be German Ebay, even after shipping to the UK has been taken into consideration...Hi Jesus, have not had luck with acquiring 16x6j alloys at an affordable price, (cant make contact with Martin -Buckalec- who seems to have some coming free), but have fitted 235x85x16 tyres to the steel rims in the meanwhile- (General Grabber TR's- suit my mainly road use). Much more gentle ride and as you suggested less stressed engine/gearing. Question, do you hang one of these massive spare wheels on the rear door-seems cruel? Also what tyre pressures do you use for your 235's? Best wishes, regards Tom
I had similar running temp issues with my truck last week. Flushed the cooling system through for a second time and replaced with fresh coolant and a Forte cooling system conditioner addative to boot!
Have run the vehicle for a week now and the running temp has dropped considerably. The truck currently sits @ 85-90ish either cruising or under load while going up hills.
I have a new thermostat ready to fit but will wait for a while and see how things pan out?
My truck runs on 235/85 16 Coopers, tyre noise is not apparent and the speedo reads 100% accurate according to my Garmin GPS.
Regards
Peter
Peter thanks for your info and reply. My temp issue seems to have settled and car now runs a bit below horizontalish mark next up from 80, unless labouring up slow motorway hills when it sits on that mark until the next decline or if non-stressed when it reduces to a little over 80 v.quickly. Re tyres just getting used to it on massive 235/85/16's, calmer certianly, my reading in Km's as LHD so double maths and yet readings seem up 5% up according to my GPS (speed camera) alert. What tyre pressures do you use in your Coopers?- I feel a possible Ali conversion coming on if I can afford any of the 6JX16 offerings. regards Tom
Tom,
I'm pretty sure I am running @ 2.2 Bar all round?
I need to check the wear and raise/lower accordingly..... Will keep you posted.
Regards
Peter
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23mpg is ok at that speed. If it uses no oil or water then it sounds spot onThanks for responses. It is a manual-my preference for simplicity- along with wind up windows, but it has an essential (for me) ESR. Annoyingly its the last Merc G manual model (with the 300GE), hence my search and purchase of a 16 year old car, indeed older than my last. Odd that the thermostat doesnt open fully till 95degrees, so it implies it is meant to run hot. Yet it seems happier at 90 degrees, are cooler thermostats available? You say 75-80mph, for that i seem to need a downslope and tailwind, 65 is where it is happiest and coolest and likely most economical. Perhaps this is part of the legacy and it needs reeducating. regards Tombo