2500 mule overheating effects?

[greenkit]

Firstly, thanks to all who contribute to this site: as a new Mule owner, I find it essential reading..... I'd appreciate some advice on my engine, the normal FD620D.

I just acquired this 1999 model, service history unknown (but dubious if much care was taken). I noticed overheating when I first drove it (dash light came on), the oil was greyish and way above the max level on the dipstick. The oil filler cap also had grey scum. The engine starts fine and runs well, however. There's no water vapour / white smoke from the exhaust, but a definite puffing from the oil filler cap and the dipstick access hole when running.

I've done a compression test with the engine warmed up, plugs out, and coil supplies disconnected. Turning over as per normal key start, gas pedal at ‘idle’ (min throttle) gave about 115 lb. Repeating with 3-4 squirts of clean oil into the cylinders gave 170 psi. Both cylinders are similar, within a few lb pressure.

I changed the oil and let the engine run, topping up the coolant as per the manual to get the air out: no severe bubbling at the rad filler cap and good circulation through the radiator, fan coming on, etc. A little oily scum at the rad neck, but nothing serious. Tried repeating this for a few days as the coolant fell slightly overnight. Today, BIG problems as the water pump now has a severe leak down the outer crankcase (not noticed previously) and the 'oil' is like milk with dipstick level rising fast.

So, I need a water-pump and probably have piston-ring problems. Do the compression values also indicate leaky head gaskets? Is it likely that the water pump has been the culprit from a while back, allowing coolant to pass into the crankcase / creating an airlock? The 'oil' currently present certainly won't provide much lubrication / ring sealing. Complete rebuild?

Sorry for the long post.....

[ardakota]

just my thinking if you say it runs good i would fix the water pump and go from there that may be all thats causing your problem it cant be too hard of a fix and you never know unless you try

[RCW]

The dry and wet compression test more or less focuses on the compression rings. But, milky oil is from coolant contamination.

It really depends on your intended use and budget, but if you want to spend minimum dollars I would take a different approach and pull the cylinder heads and inspect them for leakage at the head gaskets.

Unfortunately, once these gas engines get too hot they tend to warp the heads just enough to blow one or more of the head gaskets. Usually, you can fix the leakage problem with new gaskets, but sometimes it is necessary to have the heads planed just enough to get them level again.

The dry compression test is well within what I would consider good for a lot more hours of use.

If you have the budget and feel you need to go deeper and look at rings and pistons, then I would recommend a complete new engine. Once you start into these and find other problems like plastic cam gears going south, it is much more cost effective to simply do a replacement engine.

[greenkit]

Thanks to both: I've ordered a new water pump and a head gasket set. If the cylinder bore wear is not excessive I'll stop there. This Mule will be used for maybe 50 hrs/year, and only lightly, but I'd just like it to be reliable and not self-destructing. I'll post what I find.

[greenkit]

Hi again: my findings on the engine included a very badly worn water pump (shaft badly corroded), likely the main culprit in leaking water into the crankcase. The rear head gasket was quite badly burnt for about 20% of its circumference between the cylinder edge and the water channel. The front head gasket was scarred in the same region, but not burnt through. There was no piston slap and a 'nail test' showed no nasty edges in either cylinder. I was lucky in that a straight-edge test on the head / block surface didn't indicate measurable warp. There was light carboning which I cleaned off, and I re-lapped the valves with fine paste. A cold compression test now returns about 170 lb (throttle open) on both cylinders.

The engine is now running again, with the (proper) coolant keeping up in level, no water going into oil, no over-temp light. The radiator is heating uniformly and the fan turning on / off, something that didn't happen previously.

Now, the idle was too high, well over the lower limit for a crunch-free transmission engagement. This was the case when I got the mule, and before the engine fix. I don't have a tacho, but listening as the engine warmed up it appears that the idle speed increases. At full temperature, the idle screw needs to be fully out to get a just-satisfactory lower limit. The same setting when cold is stalling speed. I cleaned the carb (Mikuni BV26-1 when working on the top-end, but didn't tweak the internals. Any thoughts appreciated.....

Thanks again for previous help. My Mule is the only one locally, so I can't directly compare what it does with another: the site is really useful!

[RCW]

I would take a can of spray oil, WD-40 works fine, and start the engine and while it is idling spray around the two sides of the intake manifold where it joins both cylinder heads, and where the carburetor joins the manifold with that elbow and two gaskets. If the idle speed changes while spraying the oil, then you have a vacuum leak and will need to resolve that first.

Usually when the high idle that cannot be turned down with the throttle stop screw occurs it is a combination of a vacuum leak and too high a float level, or a vacuum leak and the carburetor float valve is leaking from a bad Viton (synthetic rubber) tip on the needle and not shutting off where it should - a slight shadow on the tip is too much wear.

The other common problem is misadjusted governor linkage. If that linkage is set too tight or missing one of the springs it will run at a high idle that will cause all sort of diagnostic nightmares.

The governor is listed on Kawasaki.com in the parts section as the "control." Take a look at the diagram and make sure everything is present on yours. Also be sure to check the primary speed stop screw on that linkage to make sure it is properly adjusted.

If you want to avoid future water pump failures put a small jar of Barrs Leak in the coolant in the engine, not in the overflow tank. That neutralizes and coats the metal surfaces and prevents rust, and it lubricates the water pump seal. I have never had to replace a water pump once Barrs Leak was used. Use the genuine Barrs Leak that has the oily fluid and the stuff that looks like rat droppings, anything else is a waste of time and will not work. Do not waste your time on the Barrs Leak tablets, they are also useless, you want that oily fluid from the bottled type in the cooling system.

[greenkit]

RCW, many thanks: I will check as you suggest. I should have added previously that performance higher up the throttle range appears fine, though there's a bit of 'deadness' in response initially. The governor linkage cover has never been off I'd say (rivets appear original). In testing, I backed the governor stop screw off completely and relied on the carb idle screw for adjustment: revs were still too high at the 'fully out' position, but maybe an incorrect method?

The carb's float chamber was very clean when I looked; some further internal investigation may well be necessary when I've eliminated everything else. New territory for me!

I will get some Barrs Leak: good advice.... Your input is much appreciated.

[RCW]

It sounds like you may have a couple of issues.

The low end deadness is likely a carburetor problem with a plugged pilot circuit, or the pilot screw is set incorrectly, or the float level is incorrect. Some of these have a plastic block on the pilot screw to meet CARB emission standards. I pull that block and adjust the pilot to where they run good, then set the idle and fine tune the pilot circuit until it runs where I want.

On the idle, hold the carburetor throttle linkage fully closed on the idle stop and if the idle does not drop the problem is the carburetor. Loose throttle plate screws can keep the throttle from closing and create idle nightmares too. If the linkage will move and the idle drops, then the problem is the governor linkage or the foot throttle cable may be binding.

It would also not hurt to check your choke cable to be sure it is fully opening the choke.

The engine should idle down so low it will stop.

Some clutches do not fully release even at a very slow idle, and will continue to pull the belt over and cause the transmission to spin. That will result in grinding into gear. In that case and the clutch is good, and the belt is within specifications, then I adjust the distance between the drive and driven clutch units slightly closer so the belt quits pulling the secondary over. That will slow the Mule down a bit, but the difference between 23 and 25 mph is not that great for most people's use, and the drop in wear on the transmission is well worth the reduced speed.

[greenkit]

Ok RCW - I checked with WD40 today for vacuum leaks, but no change in idling with that test. When I had the carb off last week I checked that the throttle & choke plate screws were secure, and that the plates had full movement. The control cables are free. Today I left the idle screw fully out i.e.: the throttle control tab was right up against its molded stop on the carb body. From a cold start the engine kept going but had to be nursed from very low idle rpm for the first minute or so. Thereafter the 'idle' speed slowly built up, through what I'd say was normal, to beyond 1000 rpm; blipping the throttle caused a further rise to a slightly higher plateau value. Suggests internal 'stickiness'? Certainly after 20 mins or so the idle is way too high at minimum carb setting, no-where near stalling. So I think I need to go inside the carb?

I also noticed that although the choke was needed to start, when fully warmed up and idling it appeared to have little effect if pulled on; no stalling as I used to see on car engines with manual chokes (many years ago!).

I will arrange a tacho over the next day or two and get some real rpm numbers. It's good to know about the torque converter fix in awkward cases; experience with these machines is so very useful. Thanks again.....

[RCW]

If you are certain that the governor is not raising the idle by opening the throttle, then it is time to go into the carburetor and remove all the jets and make sure all the passages are open and clear, and quite possibly replace the float needle.

If the float needle looks good, then check the seat that is cast into the carburetor. If it wears it will leak, and is not replaceable.

There is really nothing that will stick in these carburetors, except the float valve. What puzzles me is that if you are getting excess gasoline it should start running rich and trying to flood the engine while the exhaust will smell rich. Since that does not seem to be a problem, there has to be an internal carburetor issue such as a leaky or sticking float valve combined with the pilot screw set incorrectly.

Another possible problem could be the pilot circuit. If you get a chunk of semi-mobile crud in the pilot screw chamber then the starting and idling rpm and first quarter of its power will fluctuate as the junk moves about and either opens the circuit or closes the circuit. It could also be that someone took an air hose to the carburetor and blew out one of the passage blocks (look like little balls). If the latter happens it can sometimes be fixed with a piece of shot being inserted and locked in the open passage, but most often the internal casting on that particular type of carburetor will develop pressure cracks and then the carb is simply shot.

[greenkit]

Thanks again, RCW. I'll venture into the carb and do as you suggest. From what you say / what I've seen, I'll look especially for pilot circuit contaminants.... I'll post the findings anyhow. Your help is much appreciated.

[greenkit]

Reporting on what I found in the carb: the main jet / emulsion tube all looked ok; viton needle very slightly shaded. The pilot jet was clean, but the pilot (idle mixture) screw was badly carboned / dirty. On cleaning, the taper was not badly worn, but had what I would call mild pitting / streaking to its surface. I fitted a new float valve and pilot screw, and made sure all the passages were clean by running IPA with low pressure air. The result is a much improved tickover, with only slight 'creep' upwards in rpm from a cold start. So, well worth doing.

I think this sorts out the overheating cause & effect. Moral: look after your water pump. Thanks again to RCW!

I have a couple more questions, but a new thread is called for......