1993 Thomas Saf-T-Liner Cat 3116

This topic contains 10 replies and was last updated by brian-bailey 10 years 5 months ago
August 8th, 2011 11:58pm
Hi all,

I'm relatively new to the diesel world and a recently purchased an older bus that I converted to a camper. As a result I have many questions. First a little background: This is a used bus with over 200,000 miles. I know little about the service history unfortunately. The bus has a 180 HP Cat 3116. The engine starts easily and runs well as far as I can tell. The bus is able to accelerate to highway speeds (60ish max) and I've driven it about 500 miles this year without incident.

I'll start with two questions:

1. When I first start the bus oil pressure is about 50 PSI. Once the bus warms up (less than 5 minutes) the pressure drops to below 25 PSI. It varies while driving but it's never much more than 25 PSI. This seems low to me. What should I expect for oil pressure?

2. My speedometer doesn't work at all. Where is the pickup for the speedometer? Is there a common problem can check for?
February 25th, 2012 10:52pm
The speedometer pickup should be on the right front wheel near the brake pod bracket. The oil pressure should be higher than that. I would check it with a manual guage first to determine if you guage is reading correctly. If it is correct and the filters are fresh then you need to look farther into it. Engine bearings,pressure regulator etc.
February 27th, 2012 1:07am
Minimum engine oil pressure for a 3116 at operating temperature and at idle RPM (minimum 750rpm) is 15 psi, so you are OK at idle. The fact that you are getting 50 psi on start up tells me that your oil pump is capable of making good oil pressure, and your filter probably isn't going into by-pass. However, you should see more than 25 psi under load at elevated RPMs.

Firstly, make sure you are using the correct grade of oil. I will always recommend to use CAT oil and especially CAT filters on any CAT engine. Caterpillar makes very high quality oil and filters in the interest of protecting their engines. Also, some other filter brands will have an oil by-pass valve built into the filter itself, which can open pre-maturely or malfunction, causing low oil pressure, and releasing all of the trapped contaminants into the lube system of the engine. These filters are not supposed to be used on a CAT engine. Use a CAT 1R-0739 oil filter, and SAE 10w30, API CJ-4 rated oil in temperatures between 0 F and 104 F. Any hotter than that, go with a 15w40.

Next, verifying your oil pressure guage is accurate is a must. Plumb in a guage at the oil pressure manifold on the driver's side mid engine area, next to were the original sender is located. Do all of your testing at operating temp.

If you are using the right oil and filters and your guage is accurate, I would hazard a guess that your engine bearings are worn. This is normal. Take an oil sample at the end of your oil change interval and have it analized.

P.S: If you have any more engine questions, please provide your engine's serial # prefix (eg. 2BK). This will help alot. Good luck.
February 27th, 2012 8:29pm
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February 27th, 2012 8:46pm
Thanks so much for the info. I'll take a look for the serial # and post it. I bought an oil pressure gauge kit yesterday and I'm going to check the pressure. I changed the oil and filters in June 2011. The guy at NAPA recommended straight 30 weight "fleet grade" oil that came in a 5 gallon bucket. I used NAPA filters.

I only put about 200 miles on since then but I'm thinking I'll change it anyway, and the filter too and see if that helps.

I also have a leak somewhere, only while it's running. It's hard to see where it's from exactly but it's somewhere on the transmission side of the engine, which in this case is toward the front of the bus, since it's a pusher.

Someone told me they had a topkick chevy (cat 3116) with an oil pressure issue that turned out to be a pressure relief valve in the oil pan. I was thinking if that was stuck open it might pressurize the pan and cause leaking.

Engine start easily even when cold and only smokes for a minute on warm up and under heavy acceleration. The engine seems a bit weak but it's only 180 HP in a 34 foot bus, so that may just be the way it is.

What would I expect to pay for an in-frame rebuild, ballpark?
February 27th, 2012 10:47pm
Jason is spot on with his answer about the engine.

As for the speedometer most of our Safe-T-Liners came from Detroit so corrosion is a problem in the wiring. I usually take the pickup out clean it and check the connections and continuity. Next I check the wiring from the body to the axle end. We get a lot of breaks where the wiring flexes as the steering knuckle turns. If everything checks out reconnect everything with dyelectric(s) grease in the connections and test it out on the road. Ninety percent of our failures are at the pickup or in the wiring at the axle due to corrosion.
February 28th, 2012 1:49am
Brian, your external oil leak should not be affecting you oil pressure at all. An internal leak, for example at the outlet of the oil pump, can affect oil pressure. Also, the pressure relief valve is built into the body of the engine oil pump, and when it by-passes, it sends the oil right back into the inlet side of the pump body, so it will not leak back into the pan, or pressurize the pan in any way. But first follow my recommendations posted earlier.

I would not recommend straight 30 weight oil. I would save your money and install the oil pressure guage before doing anything else. If you do find low pressure, I would change the oil and filter, but use the previously recommended grades I have mentioned. If you are operating in a temperture range that is outside of what I have outlined, please post and I will advise again.

As far as an inframe goes, I can't be accurate on a price but I would prepare to pay around $10,000 for a REPUTABLE dealer to do the work (canadian prices). I believe parts are a bit cheaper in the U.S.

Keep posting and I will be glad to help you thru this as best I can.
November 10th, 2012 1:22am
I know I'm a little late with a reply :) The older Thomas saf-t-liners has the speedo sensor on the left front wheel reading pulses from the brake drum. Later on (mid 90s?)they retreived the signal from the trans (Allison MD) output sensor which sends a signal to the Trans ECU to the Speedo. I believe you would have the wheel sensor set-up.

Regarding engine oil pressure 25 psi is about the norm when hot. The oil pumps over time do cause a low pressure symptom, we have changed a couple because of the low pressure when coming to a stop (in gear and brake application loaded at slow speed). The bus would shut down from the "Kysor shutdown" system. The oil pressure did improve 10-15 psi with the new pump. I also agree sticking with the standard 15w40.
November 10th, 2012 1:34am
Another point I wanted to add is these engines are dry sleeved so they can be in-framed but anything more and you have to pull the block. Pricey to rebuild as well. Keep the valves adjusted, these engines have a weak #5 exhaust valve. Not trying to scare you and since you're using it for recreation the chances of it getting overheated is remote. Heat and heavy loads aggravate the top end which is the only weak spot on these engines.

Here is some 3116 rebuild information from my blog:

November 5th, 2013 4:04pm
I agree with John Whelan on this issue, I have 100 of theses engines still in my fleet.I have used John's videos and materials many times for training on these engines.
November 6th, 2013 10:10am
That's awesome Roger!!

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