I thank you in advance to reading this, I know I am a women and yes this is about a Horsebox lorry a MAN 1999 horsebox which I am having huuuggeee problems with so please please bear with me boys, even though I have taken it to the garage 3 times.
I will say the quick story and sorry if it is long winded. Bought this lorry 1month ago, drove it home from Rochdale down to Abersoch, well rather it didn’t really make it, after being stuck on the M62 for 2hrs in solid traffic and crawling, managed to get on the M56 and gave her a good run, next thing STOP engine light came on and I noticed that the temp gage was right at the top. Called out assistance, they thoroughly checked her and could not understand what was really wrong, they ran her solid for 4hrs, reving the engine now and then, nothing, no water leaks or anything. Anyway on the way home following morning managed to drive 20mils and same thing happened, could water was flowing out of the small overflow pipe in the water tank but no where else. ANyway the garage has since, flushed the system out, put in a new thermostat and told me she was good to go, I only managed a 10mile trip and same thing happened again, water gage right to the top and engine stop light came on, when I saw it slowly going up I put heaters on full blast, but when the gage went up, the heating became stone cold like being in a fridge. The garage are at their wits end, head gasket is fine, oil nice and clean, we just don’t know what is going on, we live over 100miles from a commercial garage that I know of that deals with MAN, I wouldn’t even reach 10miles with her the way she is now so can’t get to the garage. My question is if there are any specialist MAN mechanic would you have any advice, bearing in mind what the garage has already done, I am at my wits end and very upset because paid £15000 for this horsebox newly converted, and we had only bought her 2hrs prior to her breaking down, the people refused to take her back as it was a private sale.
If it has a viscous fan it may have failed ,did the garage actually check the water pump was actually pumping water ,just remove top hose start engine and there should be a nice low of water …
Thanks Norb, I am printing out all suggestions and giving them to the garage on Monday, many thanks for taking the time to reply
I would also make sure the rad cooling fins are not full of mud even if you have to take it our to check it
Are we talking about a 7.5 tonne MAN or a 16/17/18 tonne MAN? …they have different engines. I am sorry to say it but for a 1999 lorry it sounds like Dobbin’s bit is worth about £14750.
it’s a 7.5t MAN I think 4 cylinder,
Does the cab tilt after the conversion? Is the header tank (water tank)behind the cab or has the rear of the cab been cut away and the tank put somewhere else? The simplest thing this could be is a blocked small bore pipe from the engine to this tank. It has been a long time since I last worked on one of these but IIRC they did suffer from air locks in the cooling system which would give the symptoms that you have.
Header tank is behind the cab, it has been flushed 3 x, problem I have and were we live is there is no proper commercial vehicle garage near me, having to rely on a local garage with a mechanic that used to be a mechanic for the local council lorries, again I will show all the replies to him, thanks everyone for taking the time and for the advice given
You should ask the garage whether a CO2 test was done to confirm that there was no problem with the head gasket. If not ask them to do one. An infra red thermometer will be useful to check whether there is a problem with the radiator. A piece of cardboard the size of the radiator core with a 4" square hole cut in the centre of it can be useful to check the operation of the viscous fan in the workshop.
Co2 test been done, no problem with the head, it is a bit baffling, but saying that not sure if they have actually thought of the fan and other things you have both mentioned
If it were mine if be pulling the water pump off to check it, while its off its worth checking the housing of the timing case cover as I’ve changed a few that have been badly cavitated. My first thought was head gasket tbh, it might be worth getting it to a garage that know a bit more about them as those little D08 motors are usually pretty bulletproof.
check all the easy things 1st, like the water pump hasn’t sheared, rads aren’t internally blocked, viscous fan is ok, then just take the cylinder heads off & have them crack tested & skimmed. 2 heads on a D0834 and 3 heads on a D0836. new head gaskets etc. otherwise you will never get anywhere, doing a gas test from previous experience isn’t always accurate. good luck.
Brilliant advice from all of you guys, really really appreciate it, and appreciate your expertise and time to post, thank you so much
Presume they’ve checked cap is ok.
Does it actually boil up,if not it could be the temp guage sender or the guage,or a bad earth on same,we had a VW T4,with same problem,was just a bad connection. 
Good Luck.
shirtbox2003:
Does it actually boil up,if not it could be the temp guage sender or the guage,or a bad earth on same,we had a VW T4,with same problem,was just a bad connection.
That was my thoughts too.
If it is boiling, as OAD has suggested, it may be the expansion tank cap leaking. This is common on Landrovers, and a leak stops the system pressurising, so the coolant boils at a lower temp.
I’d suggest spending a few pounds on a new cap, and giving it a try.